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View Full Version : How much difference can tooling make on a small, low power lathe?



Evan
07-06-2009, 10:32 AM
It can make a great deal of difference. Here is an example.

It is frequently said that negative rake carbide inserts will produce the best finish. In the same breath it is also said that they require a lot more power and rigidity to use. Both statements are more true than false but not entirely accurate. Negative rake is not the cure-all for finish problems and negative rake cutters do not necessarily require a large, rigid and powerful machine.

I was turning some schedule 40 welded seam pipe of dubious metallic content which was imported from India, that bastion of quality control and unmatched consistency of product.

I normally use hand sharpened solid carbide cutters for this, especially the first pass to remove scale. I was not seeing a good enough finish although it was passable for the purpose it wasn't quite good enough for my eye.

Recently I traded an item to Rockrat in exchange for some old stock cermet (CERamic-METallic) coated carbide inserts. They are as plain as they come, simple radiused squares with no chip breaker, no rake and symmetrical top and bottom.

http://ixian.ca/pics6/insert3.jpg

They are intended to run at a negative angle in respect of the stock surface which provides the requires clearance under the cutting edge.

I made up a tool holder from a square bar of cast iron by milling a 45 degree angled step on one end to bring the centre height on line. It is also canted to provide the correct rake angle and exposes two of the corners for use.

http://ixian.ca/pics6/insert4.jpg

I applied this to the job running the lathe at 800 rpm and taking light cuts of no more than .020" and less for the finish pass. The insert cut a near mirror finish with none of the usual tearing, skipping and other usual grief seen when turning mild steel. No lubricant or coolant was used.

http://ixian.ca/pics6/insert1.jpg

http://ixian.ca/pics6/insert2.jpg


As can be seen, even if you have a light import machine there is much you can do to improve the quality of your work by simply spending the money to buy quality tooling. These inserts have 8 usuable corners and the one I used turned at least three passes of nearly a foot by 1.5" diameter. If used for only the finishing pass on 1018 steel that equates to turning at the very least a total of 24 feet of pipe with a realistic expectation of much longer life than that.

gfphoto
07-06-2009, 11:10 AM
Evan,

Very informative post for me as I've just found a bunch of inserts of that shape and had been wondering how to use them and If I could make a holder. I think mine are plain steel or maybe carbide and without holes.

I want to make sure I understand "negative rake": is that when the cutting corner of the insert is lower than the opposite end?

Is the tool height set so that the insert contacts the work at the centerline?

Also, in the fourth photo, what it the device opposite the tool holder? Is that a kind of follower rest? And what are the Vise-Grips for?

Thanks,

Gary

Evan
07-06-2009, 11:25 AM
The vice grips are clamping the insert to a carbide tool as a test to see if I should bother to make a tool holder.

The large cone shaped object in the tailstock is a live pipe center for large hollow work.

Rake angles:

http://metalshopborealis.ca/pics/rake.jpg

The insert is set to cut at the centre line.

dp
07-06-2009, 11:28 AM
The vise grips look like part of version 1.0 of the cutter holder :) The finished tool shown later isn't in that picture.

gnm109
07-06-2009, 11:31 AM
Very helpful information. I have only just begun to use carbide inserts and as shown in your pictures they can give a very nice finish indeed when used to advantage.

I note also that you are running at 800 rpm. Apparently carbide comes into its own at higher speeds.

Thanks! :)

rockrat
07-06-2009, 11:36 AM
Its good to see your finding the inserts useful. Nice post Evan and a good point about understanding tooling.

I had ran back through my machining book from college some time ago and re-read many different things. Its amazing at what one will forget if it is not used on a regular basis.

Its also easy to just make it through something because one has the horsepower to do it. Combining all of the above requires the operator make good judgements on everything from tooling to speeds/feeds/hp to support of the work and fixturing.

Nice finish.
Cheers!
rock~

Evan
07-06-2009, 11:45 AM
I forgot to mention the common name for the pipe center. It is frequently called a bullnose center.

lakeside53
07-06-2009, 11:52 AM
Great post Evan. I have accumulated a lot of quality negative rake tooling and inserts over the past year, and had just left them to one side for a future "bigger lathe". Just the negative rake boring bars - at least 12....

Last weekend I was having all sorts of problems boring some 4340 (swath and chips catching in the tooling, tool rubbing the bore... ). I changed to the only tool that would fit well- a negative rake kennematal bar, and hey... it worked.

I have a 1hp Emco V10P. Not particularly "rigid", but it did work well - I ended with a nice bore finish and no taper.

I thought I was just lucky.. but with your post...I'll give some of my other tooling and some high quality iron pipe a try!

Bill in Ky
07-06-2009, 11:53 AM
Very informative post, thanks Evan.

Boucher
07-06-2009, 12:07 PM
Evan
1. Why did you use cast iron?
2. If you were starting from scratch and had to buy material to build tool holders. What would be your preferences?
3. From the photo it looks like the corner of the insert is unsupported for approximately one thickness. Are there any rules of thumb re insert support? For light cuts?

That really is impressive surface finish.

This is a very good and useful post that helps us wantabe HSM. Thank you for shareing.

Evan
07-06-2009, 12:14 PM
I used cast iron because of it's damping qualities and because I had a piece exactly the right size on hand. It has much less tendency to ring than steel.

Perhaps the insert could be better supported but in this application it won't see the large depth of cut that may be used on a larger machine.

The best material for a tool holder is solid carbide because it is about three times stiffer than steel. For this application steel will work just fine. However, I also designed the holder to use as a boring bar and in that use the cast iron may work a bit better than steel.

lazlo
07-06-2009, 12:26 PM
Rake angles:

http://metalshopborealis.ca/pics/rake.jpg

Right, but that picture is for hand-ground lathe tools. Negative rake inserts, including the Cermet inserts you're using, don't slope off like that -- they have 90° sides.

The reason they're negative rake inserts is because the pocket on the toolholder is cut to tip the edge down, to form the negative rake angle.
You mention that in your original post, but that picture is misleading :)


They are intended to run at a negative angle in respect of the stock surface which provides the requires clearance under the cutting edge.

To further confuse matters, positive rake inserts like TPG's are shaped like the first picture, which is entitled "No Rake." ;)

gfphoto
07-06-2009, 12:45 PM
The vice grips are clamping the insert to a carbide tool as a test to see if I should bother to make a tool holder.

The large cone shaped object in the tailstock is a live pipe center for large hollow work.

Rake angles:

http://metalshopborealis.ca/pics/rake.jpg

The insert is set to cut at the centre line.


Thanks Evan - very clear. Also interesting about the material for the tool holder.

Sorry if it wasn't clear, this is the device I was asking about:
http://www.gfphoto.com/tool/insert1.jpg

Thanks again,
Gary

Evan
07-06-2009, 12:58 PM
The rake refers to the top surface of the tool only and the angle it has relative to the work (when correctly applied).


To further confuse matters, positive rake inserts like TPG's are shaped like the first picture, which is entitled "No Rake."

They may be but they aren't a true positive rake insert. A TPG insert is "T" for triangular, "P"= has an 11 degree relief angle below the cutting edge, "G"= has a chip breaker and hole for mounting. If the insert is really positive rake the third or fourth letter will be either K, P, Q, S, Y or Z. The third letter may be left out as it is a tolerance spec code and replaced by the fourth which specifies the rake and chipbreaker style.

http://www.pgstools.com/servlet/the-template/carbideinsertidentification/Page#Cross

Evan
07-06-2009, 01:00 PM
Gary,

That is my electric power crossfeed drive. I have variable speed reversible power drives on both axes.

lazlo
07-06-2009, 01:14 PM
The rake refers to the top surface of the tool only and the angle it has relative to the work (when correctly applied).

With inserts, "positive" or "negative" refers to the way the combination of the insert and the toolholder position the cutting angle in relation to the workpiece.

Which is why a "negative" rake insert like the SNGA you're using has vertical sides: the combination of the square sided insert with the corresponding toolholder (like you've made) that tips the insert down creates the negative rake angle.

So you can take a negative rake insert with a positive rake chipbreaker, and the combination of the insert angles and the toolholder pocket make a positive rake tool, like Ted Edwards' famous lathe toolholders:

http://www.metalwebnews.com/howto/toolholder/toolholder.html

Peter.
07-06-2009, 01:21 PM
Great post Evan :up:

How does one overcome the problem of making interrupted cuts with carbide insert tooling so that the insert doesn't chip - or is it a case of 'no can do'?

Evan
07-06-2009, 01:22 PM
With inserts, "positive" or "negative" refers to the way the combination of the insert and the toolholder position the cutting angle in relation to the workpiece.


That is what "correctly applied" means.


You could use that exact same insert, and cut the toolholder pocket to tilt it up, and make it a positive insert.

No you can't. It has zero clearance. It must be presented at a negative angle to cut.

lazlo
07-06-2009, 01:26 PM
No you can't. It has zero clearance. It must be presented at a negative angle to cut.

Red Ted Edward's article -- the chipbreaker gives you the clearance. All that matters is the final angle that's presented to the workpiece.

Michael Edwards
07-06-2009, 01:33 PM
Red Ted Edward's article -- the chipbreaker gives you the clearance. All that matters is the final angle that's presented to the workpiece.


The inserts in the article by Ted Edwards are of the positive/negative rake type, which is different than the negative rake insert that Evan is using. Evan is correct. There is a good drawing of this in Machine Shop Practice vol 1.

ME

Evan
07-06-2009, 01:35 PM
How does one overcome the problem of making interrupted cuts with carbide insert tooling so that the insert doesn't chip - or is it a case of 'no can do'?


That really depends on the grade of carbide. Not all carbide grades chip easily. I often use solid C1 carbide cutters that are recommended for heavy intermittent roughing cuts in sand cast iron. The pieces I have are very old stock originally used for debarker machines and must withstand hitting rocks. They not only don't chip easily but when they do they expose a fairly good cutting edge as they tend to flake off the underside of the top face when they chip.

This insert had no problem with cutting the weld line when I bored the inside. It still shows no wear.

lazlo
07-06-2009, 01:41 PM
The inserts in the article by Ted Edwards are of the positive/negative rake type, which is different than the negative rake insert that Evan is using.

They're both negative rake inserts with flat sides. The only difference is that the TNMP insert that Ted uses has a postive rake chipbreaker, which gives you the clearance to tip the negative insert enough to get a positive rake angle. So Evan's SNGA negative insert has the profile (flat sides) of the top insert (sans the chipbreaker groove), and Ted Edward's negative insert has the middle profile, and he tilts the insert down 5° to get a positive rake.

You could use a more severe chipbreaker like the TNMS insert at the bottom, tip the insert even more (10°) and get even more positive:

Note that these are all negative rake inserts:

http://www.plastools.com/insert3.gif

Quetico Bob
07-06-2009, 02:27 PM
Thanks for the super info Evan, great post. I have good luck with TNMG and the ones I use don’t seem to mind interrupted cuts.

Cheers, Bob

Glenn Wegman
07-06-2009, 03:13 PM
Before everyone runs out and purchases tool holders and anything that says "Cermet", Cermets are classified in the Carbide family, but are their own thing. Not all Cermet inserts are the same, just as not all Carbide inserts are the same. There are many compositions, chip breaker configurations, and edge preps. I have been using them for years and have a variety of different types, all of the same insert style. Some are sharp edge, some are honed edge, all sorts of different chip breakers and land widths, etc, and all perform differently on different substrates. To make a statement that all Cermets work and everyone should try some is like saying all dogs are brown. Evan's calling his a Cermet coated carbide is also a bit misleading as Cermet is not a coating. Evan's inserts are most likely bare Cermets (not meant to criticize Evans statement). Cermets do however come with coatings on them and are able to run at much higher surface speeds than carbide as they are much more heat resistand and durable. Cermet is also nothing new, as it was first developed in the 1920's, however, it has been developed and refined considerably since, as has Carbide.

Just a warning, so do a little research before you grab the first pack of Cermets you see on eBay and have less than acceptable results!

However, as Evan discovered, with the right combination of insert, substrate, and surface speed, they are near impossible to beat for a nice finish!

quasi
07-06-2009, 03:54 PM
that is a great finish quality for pipe.

gfphoto
07-06-2009, 04:32 PM
Gary,

That is my electric power crossfeed drive. I have variable speed reversible power drives on both axes.

Cool! Thanks!

Gary

lazlo
07-06-2009, 05:07 PM
that is a great finish quality for pipe.

Yes, definitely! I'm really curious about trying Cermets now too :)

Glenn: I've read in the trade rags that modern Cermets are a whole lot more durable than they were just a couple of years ago -- has that been your experience?

Glenn Wegman
07-06-2009, 05:25 PM
Lazlo,

I needed to turn a part that was 2" diameter, 46RC, and had two keyways cut in it. I used a coated cermet at 1200 rpm and it did just fine. It's by far the most durable Insert I have used. It was a Sumitomo T2000Z and was not the recommended grade for an interrupted cut, which would have been a T3000Z so I can't imagine how tough that one must be!


Here's another example.

I've always been a Carbide guy and am constantly hearing how HSS is superior for finishing due to it's sharpness, bla bla bla. I cut this piece of steel stock from right to left to the shoulder with a fresh stoned HSS tool bit because I got tired of hearing about it. I then went over it half the distance with my favorite negative rake Cermet insert at .001" doc with coolant and got a near perfect finish as you can see. The .001" doc is because I got tired of hearing how you can't take light or finish cuts with negative rake inserts. It's just a case of having the right combination! The biggest problem that I see is people that have used HSS forever decide to try Carbide so they go get a Chinese brazed tool bit from Harbor Freight or some generic inserts off of eBay and try to use them like they do HSS and get terrible results, and then can't wait to tell everyone the carbide doesn't work! HSS is HSS and the grinding/sharpening is the difference between success and failure where with Inserts there are literaly thousands of different grade, configuration, speed, feed, combinations that all play a part in getting the right finish.

http://img.photobucket.com/albums/v647/Fighter1/P2170009.jpg
Glenn

camdigger
07-06-2009, 06:09 PM
HSS is HSS and the grinding/sharpening is the difference between success and failure where with Inserts there are literaly thousands of different grade, configuration, speed, feed, combinations that all play a part in getting the right finish.

Glenn

No doubt the carbide vs HSS debate will rage on and on.

I've had very mixed results and I've gotten stuck with some inserts sold only in 10's from the supplier in the big city 2 hours away from my shop that are worse than dull HSS. They squeal, don't cut freely, and leave a finish that looks like it was gnawed on by rodents. Having said that, the same supplier sold me some others that work well, cut freely, leave a good finish. My point is this, I have neither the time nor resources to go through all the 100s of combinations of carbide to come up with something that works. For the price of an insert, I can buy a HSS blank and change it as I need to to get acceptable results...

Evan
07-06-2009, 06:14 PM
Glen,

I misinterpreted the listing of those inserts when I looked them up originally. This is what I read when I checked them out. Note the category on the left.

http://ixian.ca/pics6/cermet.jpg

It is however a TC30 grade cermet intended for high speed machining and fine finishes.

Quetico Bob
07-06-2009, 06:18 PM
QUOTE
I have neither the time nor resources to go through all the 100s of combinations of carbide to come up with something that works.
QUOTE

Talk to a rep. Wanted an all around general purpose insert and have been very happy with the results, just ordered another 10.

Cheers, Bob

Evan
07-06-2009, 06:18 PM
For the price of an insert, I can buy a HSS blank and change it as I need to to get acceptable results...

There is nothing stopping you from resharpening an insert. All you need is a small diamond wheel. It works with both carbide and cermets. While you cannot restore the exact same edge shape it originally had you can certainly gain a lot more useful life from an expensive insert.

Quetico Bob
07-06-2009, 06:23 PM
QUOTE
There is nothing stopping you from resharpening an insert
QUOTE

I use a hand diamond lap. More frequently on parting inserts.

Cheers, Bob

Glenn Wegman
07-06-2009, 06:31 PM
My point is this, I have neither the time nor resources to go through all the 100s of combinations of carbide to come up with something that works. For the price of an insert, I can buy a HSS blank and change it as I need to to get acceptable results...

Exactly.

That was the point I was trying to make a post or two ago in regards to Evan's hitting the right combination. There is really no easy way to figure it all out, and I have had the same experience with carbide as you did with asking a manufacturer for advice on the proper insert for the job. The finish was terrible! I do think that if you find a Cermet grade with a sharp edge that falls under the "finishing" or "fine finishing" column, you will experience some pretty satisfactory results as Evan did. It is truely a "when in doubt, speed it up" type of insert as the higher the surface speed, the better the finish, as long as your machine can stand it without chattering. it's nearly impossible to run one too fast. That's the hardest part to get used to after using HSS.

Evan,

I see the confusion. Looking accross the top of the page, as you discovered, you will see three different columns of insert types, Cermet, Coated, and Carbide.

Thanks,

Glenn

lazlo
07-06-2009, 06:46 PM
I see the confusion. Looking accross the top of the page, as you discovered, you will see three different columns of insert types, Cermet, Coated, and Carbide.

If anyone's interested, this is one of the better articles I've read about Cermets. Apparently the technological advance that's made cermets much less fragile than they used to be is micrograin ceramics (same basic technology as micrograin carbide):

Cermets Get Assertive (http://www.mmsonline.com/article.aspx?id=14980)

The toughness of this material has improved. Today, the applications for cermet inserts go well beyond finishing.

http://www.mmsonline.com/uploadedImages/Publications/MMS/Articles/Internal/Cermet%20grade.gif

camdigger
07-06-2009, 06:47 PM
There is nothing stopping you from resharpening an insert. All you need is a small diamond wheel. It works with both carbide and cermets. While you cannot restore the exact same edge shape it originally had you can certainly gain a lot more useful life from an expensive insert.

Other than removal of too much material off the edge of the insert will allow the holder to drag on the work trashing a holder worth as much or more than the insert:rolleyes:

camdigger
07-06-2009, 06:51 PM
It is truely a "when in doubt, speed it up" type of insert as the higher the surface speed, the better the finish, as long as your machine can stand it without chattering. it's nearly impossible to run one too fast. That's the hardest part to get used to after using HSS.



It's hard to believe speeding up the process will improve the excessive infeed pressure, squealing, and crappy finish from one insert when another does the job as setup without complaint.

The lathe should be big enough for carbide - it's a 2 hp 1440 with an 8" chuck.

P.S. àsk an expert`` I did. Every rep at the counter at ACT in Cowtown had input into the selection....

Quetico Bob
07-06-2009, 06:54 PM
QUOTE
Other than removal of too much material off the edge of the insert will allow the holder to drag on the work trashing a holder worth as much or more than the insert
QUOTE

Oh come on, get real! Do you actually realize how much touching up that would take? And by that time, anyone with half a brain would rotate or flip the insert….Gawd.

Cheers, Bob

camdigger
07-06-2009, 07:12 PM
QUOTE
Other than removal of too much material off the edge of the insert will allow the holder to drag on the work trashing a holder worth as much or more than the insert
QUOTE

Oh come on, get real! Do you actually realize how much touching up that would take? And by that time, anyone with half a brain would rotate or flip the insert….Gawd.

Cheers, Bob

Not a whole lot.... the holder base is already proud of the lower edge of the insert. These were a selection to fit holders included with the lathe. my half brain says I got a bad recommendation and I'm stuck with 8 new inserts that don't f%^$#g work.

Quetico Bob
07-06-2009, 07:23 PM
QUOTE
my half brain says I got a bad recommendation andI'm stuck with 8 new inserts that don't f%^$#g work.
QUOTE

Next time call Kennametal or who ever supplies you direct. That way the other half can focus on what’s important….making chips.:)

Cheers, Bob

Glenn Wegman
07-06-2009, 07:29 PM
Here's a sharp edge negative rake Cermet showing a coil (about 3' long) it peeled off of 304ss at .100" doc at 375 fpm. Cuts it effortlessly like it was leaded steel. It's evident by the limited chip breaker area that it is definitely a finishing insert and not an insert for large doc. I use this one for aluminum, some hardened steels, and stainless. It was also done on a very ridgid 6 hp 14" lathe so YMMV.

http://img.photobucket.com/albums/v647/Fighter1/Cermet.jpg

Evan
07-06-2009, 09:01 PM
Other than removal of too much material off the edge of the insert will allow the holder to drag on the work trashing a holder worth as much or more than the insert


So don't do that.

lakeside53
07-06-2009, 09:50 PM
I just bought a bunch of tooling, and found a few pounds of worn indexable carbide. The guy never threw anything away - soldered the worn inserts to a steel shank and ground then to his liking... nice;)

Mcgyver
07-06-2009, 10:46 PM
I just bought a bunch of tooling, and found a few pounds of worn indexable carbide. The guy never threw anything away - soldered the worn inserts to a steel shank and ground then to his liking... nice;)

I've seen that in a lot of machinists tool kits. all manner of lathe, fly cutters and boring bar cutters homemade from worn inserts

wierdscience
07-07-2009, 12:21 AM
There is nothing stopping you from resharpening an insert. All you need is a small diamond wheel. It works with both carbide and cermets. While you cannot restore the exact same edge shape it originally had you can certainly gain a lot more useful life from an expensive insert.

If it's a double sided insert there very much is.Sharpening one decreases the support for the opposite side when the insert is flipped over.Un-supported carbide as we know snaps off nearly instantly and on inserts it usually snaps back close enough to the hole to ruin the insert.It's false economy to touch up and insert unless it's the last cutting edge on the last insert you have on Saturday afternoon 30 miles from town:)

Circlip
07-07-2009, 04:43 AM
Wonder what my long deceased mentors would have made of this one as a "Polished" finish would have been met with "Tha rubint' metal off and not cuttin it" an even matt grey being the order of the day.

Regards Ian.

Evan
07-07-2009, 06:44 AM
It works the same as a butter knife scraping some butter from a cold lump. Funny thing is that it is really still cutting. It will make tiny fine ribbons of swarf so thin you can barely see them if you have it set to barely touch.

Peter.
07-10-2009, 05:00 PM
They're both negative rake inserts with flat sides. The only difference is that the TNMP insert that Ted uses has a postive rake chipbreaker, which gives you the clearance to tip the negative insert enough to get a positive rake angle. So Evan's SNGA negative insert has the profile (flat sides) of the top insert (sans the chipbreaker groove), and Ted Edward's negative insert has the middle profile, and he tilts the insert down 5° to get a positive rake.

You could use a more severe chipbreaker like the TNMS insert at the bottom, tip the insert even more (10°) and get even more positive:

Note that these are all negative rake inserts:

http://www.plastools.com/insert3.gif

I've just bought some cheap Iscar TNMP inserts from eBay to try this out. No idea if the grade is suitable for my needs (they were the only TNMP's offered) but for £8 delivered for 10 inserts I get 60 cutting edges to experiment with and the worst it'll be is the worlds cheapest failed experiment. The ad said the chipbreaker was designed for cast iron.

I'm going to make a couple of turning tools and a boring bar to hold them I guess.

Evan
07-10-2009, 05:48 PM
Note that these are all negative rake inserts:


Not according to ANSI nomenclature. For the 4th letter the "G" is zero rake with chipbreaker and the "P" and "S" are positive rake inserts. Strangely enough they are exactly what they look like.

From the link I posted above:
http://ixian.ca/pics6/insertkey.gif

lazlo
07-10-2009, 05:58 PM
Not according to ANSI nomenclature. For the 4th letter the "G" is zero rake with chipbreaker and the "P" and "S" are positive rake inserts.

The second letter in the ANSI/ISO designations specifies the rake/clearance angle. Negative rake inserts, like the TNMP, TNMG, TNMS inserts I posted, and the SNGA cermet you have, have 0° rake angle. They have square sides, and get the negative rake angle by virtue of the toolholder.

The 4th letter in the ANSI/ISO designation specifies the hole and the chipbreaker. So a TNMP is a negative rake insert with a 10° positive chipbreaker. A TNMK is a negative rake inserts with a 5° positive chipbreaker, etc.

Evan
07-10-2009, 06:07 PM
The second letter specifies the relief angle only, not the rake. Rake refers to the angle the top of the cutting edge makes to tool centerline (normal). That is specified by the 4th character.

The second letter codes:

http://ixian.ca/pics6/relief.gif

lazlo
07-10-2009, 06:09 PM
I've just bought some cheap Iscar TNMP inserts from eBay to try this out. No idea if the grade is suitable for my needs (they were the only TNMP's offered) but for £8 delivered for 10 inserts I get 60 cutting edges to experiment with and the worst it'll be is the worlds cheapest failed experiment.

I really like the TNMP and CNMP inserts (negative rake insert with a positive chipbreaker) -- they're really the best of both worlds: they have the strong edge of a negative rake insert, with enough back rake from the chipbreaker that you don't need immense power and rigidity.

Plus, with a negative rake insert you get twice the number of cutting edges: they have square sides, you can just flip them.

I bought a CNMP boring bar from Hemly Tool (a member here), and it's one of my favorites.

lazlo
07-10-2009, 06:23 PM
The second letter specifies the relief angle only, not the rake. Rake refers to the angle the top of the cutting edge makes to tool centerline (normal). That is specified by the 4th character.

Yeah, I didn't think you were getting my point earlier in the thread. All negative rake inserts have square sides, which is designated by a 0° clearance/rake -- the "N" in the second letter of the ANSI designation. The negative rake angle is generated by the toolholder.

http://i164.photobucket.com/albums/u15/rtgeorge_album/ANSI.jpg

The 4th letter in the ANSI designation specifies the hole and chipbreaker pattern:

http://i164.photobucket.com/albums/u15/rtgeorge_album/Hole.jpg

Evan
07-10-2009, 06:33 PM
I really like the TNMP and CNMP inserts (negative rake insert with a positive chipbreaker)

They are not negative rake inserts and continuing to say they are will not make it so.



Insert designation used by the standards organization. Examples of this attribute are provided below. From ANSI B212.4-1986, the 10 symbol designation is as follows:
1) letter identifying insert shape,
2) letter identifying cutting edge clearance (relief) angle(s),
3) letter identifying tolerance class,
4) letter identifying surface type features,
5) one or two digit number identifying size of inscribed circle or width and length of insert,
6) one or two digit number identifying insert thickness,
7) letter or number identifying cutting point configuration,
8) number identifying edge length of facet,
9) letter identifying feed direction,
10) letter identifying edge treatment and surface finish. Example (inch dimensions): S H C N - 6 3 D 8 R T

From ISO 1832-1991, the 10 symbol designation is as follows:
1) letter identifying insert shape,
2) letter identifying normal clearance,
3) letter identifying tolerance class,
4) letter identifying fixing and/or chip breakers,
5) number identifying insert size,
6) number identifying insert thickness,
7) letter or number identifying insert corner configuration,
8) letter identifying cutting edge condition,
9) letter identifying cutting direction, and
10) manufacturer's symbol, optional. Example (metric dimensions): T P G N 16 03 08 E N - X


Insert Rake Angle The manufacturer's specification of the rake angle for the insert. The rake angle is the inclination of the tool face against which chips are severed (i.e., the rake face).

The rake face is that surface over which the chips bear as they are being severed. If the inclination of the face makes the cutting edge keener or more acute, the rake condition is defined as positive. If the inclination of the face makes the cutting edge less keen or more blunt, the rake is defined as negative.

Also called Top Rake Angle or Axial Rake Angle. The angle of inclination of the rake face toward or away from the end or end cutting edge of the tool, measured in a plane that passes through the side cutting edge and is perpendicular to the base of the to ol body shank. If the angle of incline is away from the end cutting edge, the Back Rake Angle (i.e., axial rake) is positive. If the angle of incline is downward toward the end cutting edge, the Back Rake Angle (i.e., axial rake) is negative.


http://www.mel.nist.gov/msidlibrary/doc/jurrens95a/resourcc.htm

Evan
07-10-2009, 06:34 PM
The negative rake angle is generated by the toolholder

There in NO ANSI spec for tool holder rake.

lazlo
07-10-2009, 06:38 PM
I really like the TNMP and CNMP inserts (negative rake insert with a positive chipbreaker) They are not negative rake inserts and continuing to say they are will not make it so.

God, you're hard-headed Evan. Open up a basic machine shop book once in awhile:

http://i164.photobucket.com/albums/u15/rtgeorge_album/Negative.jpg

lazlo
07-10-2009, 06:46 PM
http://i164.photobucket.com/albums/u15/rtgeorge_album/CNMP.jpg

Glenn Wegman
07-10-2009, 07:11 PM
I really like the TNMP and CNMP inserts (negative rake insert with a positive chipbreaker) -- they're really the best of both worlds: they have the strong edge of a negative rake insert, with enough back rake from the chipbreaker that you don't need immense power and rigidity.
.

Lazlo,

If you like those you will really like the TNGP, CNGP inserts.

Give one a try!

Glenn

Evan
07-10-2009, 07:23 PM
Your last example is a postive rake insert, by definition. It says so in the specifications.

http://ixian.ca/pics6/insert6.jpg


God, you're hard-headed Evan.

Why yes I am when faced with incorrect information being dispensed as truth.

lazlo
07-10-2009, 11:06 PM
If you like those you will really like the TNGP, CNGP inserts.

Give one a try!

I'd love to try those ground inserts. Like many here, I love the CCGT's (ground positive rake insert) for aluminum, but for some reason, most of the ground negative rake inserts on Ebay are in the 4xx series size, and the biggest holder I have is a 3xx series.

I know you can order the CNGP-332 on MSC et al, but those are $6 and up per insert...

lazlo
07-10-2009, 11:36 PM
http://i164.photobucket.com/albums/u15/rtgeorge_album/CarbideDepot.jpg

The 4th letter is the chipbreaker designation. CNMP negative rake inserts normally come with a 5° positive chipbreaker. That particular insert has a 10° positive A.K.A "double-positive" chipbreaker:

http://i164.photobucket.com/albums/u15/rtgeorge_album/Hole-1.jpg

http://i164.photobucket.com/albums/u15/rtgeorge_album/CNMP2.jpg

You linked to the Valenite CNMP insert. Here is an explanation of negative rake inserts with positive chipbreakers from the Valenite Tech Engineer, from

http://www.thegallos.com/response.htm
Valenite

From: FirstName LastName, on 3/12/98 4:10 PM:
To: INTERNET[GALLO@XXXXXXXXX.COM]

Hi, I'm with Valenite Cutting Tools, FirstName LastName from Cincinnati Milacron asked me to respond to your request for information.

I understand the challenges the home shop faces with regard to using carbide tooling. The advantages of carbide vs. hss are well documented for large shops and hi production and the same can be said for home shops but cost is a big concern for the hobbiest.

I agree with you in your selection of TPG or ISO positive rake type tooling with respect to rigidity and horsepower limitations however both are single sided inserts which are not the most economical choice. Fortunately a lot of progress has been made in the last few years in the chip groove geometries found on negative inserts (cnmg, tnmg , etc.). These "chipbreakers" can produce positive shear angles in negative rake tooling which reduces tooling pressures and horsepower requirements in a double sided insert. This combination of geometry and economy may be advantageous for the home shop.

oldtiffie
07-10-2009, 11:47 PM
The title of the thread is:
How much difference can tooling make on a small, low power lathe?

Are we still "on topic" - ie for lathes similar to Evan's belt-driven SB - and similarly powered lathes, or have we moved "off" - or "on" - again?

lazlo
07-10-2009, 11:53 PM
The title of the thread is:
How much difference can tooling make on a small, low power lathe?

Are we still "on topic" - ie for lathes similar to Evan's belt-driven SB - and similarly powered lathes, or have we moved "off" - or "on" - again?

The point I've been trying to make is that Evan is showing that negative rake tooling can be used on a low-power, Home-shop grade lathe. But he's using an Old School flat-topped SNGA insert. A modern negative rake insert with a positive chipbreaker can greatly reduce the horsepower and rigidity requirements for a HSM'er.

The ground inserts like Glenn was suggesting have an even sharper edge than the molded (xNMG) inserts, which further reduces the horsepower and rigidity necessary to drive these inserts.

oldtiffie
07-11-2009, 12:33 AM
Thanks Lazlo.

That's cleared it up nicely.

The main reason I asked is that many here have "low power(ed)" lathes and this discussion may encourage some to move out of the "HSS comfort zone" and make more or better use of their lathe without flogging or hammering them.

The same principles apply to milling machines - perhaps even milling in the lathe - as some do - hopefully with collets - but "chucking" it can work.

Again, many thanks - especially for the very informative diagrams and illustrations of the types and uses of those "tips" and "inserts".

torker
07-11-2009, 12:47 AM
The VERY best finish I've ever obtained was with a square chipbreaker insert that I made a toolholder for...for my ol' SB9 @400rpm (maxed out)
Turning annealed 4140...the finish was flawless.
Russ

toastydeath
07-11-2009, 02:55 AM
Lazlo is nailing it.

If I had read this thread at work today, I'd have taken pictures to show what he's talking about for those still confused.

Toolholders usually angle the insert downward by 3, 5, or 7 degrees. That, by definition, adds 3-7 degrees of clearance on a neutral insert, and subtracts 3-7 degrees of rake off your insert.

So say I pick up a toolholder with 3 degrees of rake on it. And say I pick up an insert with 13 degrees of rake. That means my zero-clearance insert now has 3 degrees of clearance, and 10 degrees of rake in that toolholder.

If I stuck it in the 7 degree toolholder, I'd have 7 degrees of clearance and 6 degrees of rake.

For those who don't believe Lazlo, just go look in any tool supplier's catalog - Sandvik, Kennametall, Iscar, whoever. The toolholders are all sold by pocket inclination in addition to lead angle, insert type, size, etc.

For our HLV clone, I use very positive (20-35 degrees of positive rake) stainless steel finishing inserts from Sandvik that have a long (~.4") cutting edge and are capable of deep cuts. They work brilliantly on just about everything.

Peter.
07-11-2009, 04:52 AM
Arguing semantics in the middle of a good thread :(

It's a matter of how different people/companies use the terminology - what does a small difference matter so long as the understanding is conveyed.

Reminds me of my school metalwork teacher who would go nuts if he heard the term 'drill bit'. "This is not a drill bit - it's a DRILL. You put it in a DRILLING MACHINE - there's no such thing as a DRILL BIT!". When someone pointed out the lists of 'drill bits' in his catalogue he went purple and had to go sit in his office.

Whilst we are on the subject of carbide inserts - is there a standard terminology for 'grades' of inserts that make it easy to determine which grade is best suited to the HSM'er. I had no choice but to buy IC20 K10 grade as it was the only one offered but in the case of many grades being available I'd like to be able to refer to a chart or something.

BadDog
07-11-2009, 05:15 AM
The ground inserts like Glenn was suggesting have an even sharper edge than the molded (xNMG) inserts, which further reduces the horsepower and rigidity necessary to drive these inserts.
I'm not even getting into the other part. But a small point, and I'm sure you are aware, but others may not be. That 3rd position is actually "tollerance". "M" is not "Molded", and "G" is not "Ground", though it works out that way often enough that it's a decent mnemonic.

Reference Chart (http://www.carbidedepot.com/formulas-insert-d.htm)

Evan
07-11-2009, 07:48 AM
What we are left with according to Robert's interpretation is that the ANSI code does NOT specifiy whether the insert is positive or negative. The second letter only refers to the clearance angle and not the top rake. The only information we can use to determine the rake angle of the cutting edge is the 4th letter which strangely enough provides us with the positive vs negative rake angle information of the cutting edge. The 4th letter specifies not just the chipbreaker shape but the tool GEOMETRY according to it's surface features.

That is why the ANSI standard does not refer to the fourth letter as indicating chipbreaker style but instead surface features. Surface features obviously includes the cutting edge and a negative rake cutting edge is one that is presented to the work with plane of the cutting edge inclined toward the work.

How the tool holder is positioned means nothing without the information about the included angle of the cutting edge to the relief angle. That is why there is no ANSI standard for tool holder angle. Clearance on a zero relief angle tool can be easily obtained by cutting slightly below the centreline of the work. Cutting at some position other than at centreline if frequently done when boring to provide adequate clearance for the bar.

Calling an insert a negative insert when the cutting action is via an edge with a positive rake angle to the work in actual use is at the least misleading and inconsistent with the ANSI identification code. If we are to accept that interpretation then we no longer have the ability to identify the type of insert geometry via the ANSI code.

Glenn Wegman
07-11-2009, 08:34 AM
The ground inserts like Glenn was suggesting have an even sharper edge than the molded (xNMG) inserts, which further reduces the horsepower and rigidity necessary to drive these inserts.

And I will further mention that the CNMG (CNGP) or TNMG (TNGP) style are amoung the most common and inexpensive as far as price per insert. The best part is that since they are 0° relief and are used in Negative Rake tooling, you are able to flip them over and use both sides. This gives you a possible six cutting edges on a TNMG style, and four on a CNMG style if you have the more comon style holder, and four more for a total of eight edges if you incorporate a second style holder to utilize the obtuse corners as I do with this combination of tool holders.

http://img.photobucket.com/albums/v647/Fighter1/CNMG-1.jpg

Using positive rake tooling that needs the relief ground on the insert only utilizes the top side of the insert where negative rake tooling with 0° relief on the inserts allows for use of both sides which is much more economical.

I have no intention of trying to "convert" anyone with a smaller lathe or HSS to Indexable tooling, but this may be of interest to those who want to try carbide or other indexable tooling etc.

Glenn

Peter.
07-11-2009, 08:38 AM
The fact is though that Lazlo's use of terminology managed to convey his meaning perfectly to at least my novice's mind. Since many HSM'ers are novices like myself this is the kind of post we find easiest to assimilate, not arguments on technical exactness.

Glenn Wegman
07-11-2009, 08:52 AM
Excellent point Peter!!

As far as your question about a grade chart:

Each manufacturer has their own grade designation for inserts so you would need to go to a specific manufacturer to research what grade they recomment for your purpose.

Another method, if you plan on browsing eBay for inserts, is to look it up according to it's listed grade. Find an interresting looking insert and then go here. http://www.carbidedepot.com/. As long as the manufacturer's Icon is shown on this page, just click on the icon and that will take you to a support page for that manufacturer. Then click on the link next to "Online application support" and that page will have lots of links to different sorts of info. I use the "Grade look up" link and type in the grade listed on the insert on eBay and it will tell you what it's primary use is.

Sounds complicated, but it isn't bad once you do it a few times.

Glenn

Peter.
07-11-2009, 09:09 AM
That's brilliant Glenn - thanks a lot.

Got me straight here (http://www.carbidedepot.com/iscar-gradecharts.htm) and since I have IC20 K10 it tells me just about everything I need. Nice to see they will be good for stainless as I do a fair bit of machining of that for my bike.

J Tiers
07-12-2009, 07:33 PM
It can make a great deal of difference. Here is an example.

It is frequently said that negative rake carbide inserts will produce the best finish. In the same breath it is also said that they require a lot more power and rigidity to use. Both statements are more true than false but not entirely accurate. Negative rake is not the cure-all for finish problems and negative rake cutters do not necessarily require a large, rigid and powerful machine.

I was turning some schedule 40 welded seam pipe of dubious metallic content which was imported from India, that bastion of quality control and unmatched consistency of product.

Recently I traded an item to Rockrat in exchange for some old stock cermet (CERamic-METallic) coated carbide inserts. They are as plain as they come, simple radiused squares with no chip breaker, no rake and symmetrical top and bottom.

I applied this to the job running the lathe at 800 rpm and taking light cuts of no more than .020" and less for the finish pass. The insert cut a near mirror finish with none of the usual tearing, skipping and other usual grief seen when turning mild steel. No lubricant or coolant was used.

As can be seen, even if you have a light import machine there is much you can do to improve the quality of your work by simply spending the money to buy quality tooling. These inserts have 8 usuable corners and the one I used turned at least three passes of nearly a foot by 1.5" diameter. If used for only the finishing pass on 1018 steel that equates to turning at the very least a total of 24 feet of pipe with a realistic expectation of much longer life than that.

Not sure what the problem is here......

1) Evan is running "carbide type" speeds, over 300 FPM with material which nominally would be cut at 100 with HSS. (he states 1.5" OD) usual quote is 2x to 3x the HSS speed for carbide, presumably similar for cermets, if not higher.

2) the cuts of 0.020 are well within the range normally suggested for carbides, which is generally more than 0.005 DOC. I hae taken off 0.001 type cuts with TNMG inserts, but it isn't normally a swift idea.

The major issue with the use of this type technique is having the power to turn the part against the tool. presumably the 0.020 and lower is OK at those speed, power-wise.

the secondary issue is whether the machine can take the pressures, but unless your machine is particularly obnoxious, it should be fine with those light cuts.

REAL carbide cuts are similar to taking off 0.5" DOC at high FPM... that takes power and rigidity.

The machine in the pics looks like Evan's SouthBend, although I suppose it could be something else. Does not look like a 9 x 20, which is the poster child limber and bouncy import machine.

I'd never argue carbide is useless on a lightweight SB or whatever. Sometimes you need to use it.

As to whether you can count on that sort of mirror finish, that's another issue. The sweet spot can be hard to find.

Evan
07-12-2009, 08:28 PM
The issue is one about insert nomenclature. It seems that the ANSI nomenclature for insert designation is meaningless. It is being argued that the rake of the cutting edge relative to the work does not determine the insert type as per ANSI nomenclature. In actual fact it does although apparently you may need to buy what is being called a negative insert in order to get a positive one. Proper interpretation of the ANSI labeling system does reveal the type of insert which is of course the objective of a standard.

The argument posed by Robert results in the rather awkward circumstance of specifiying a negative rake insert to obtain one with a positive rake cutting edge. He has also made some statements that are flat out incorrect, such as that the second letter of the insert identification system indicates the rake angle of the cutter when in fact it only specifies the clearance angle below the cutting edge.

dp
07-12-2009, 08:45 PM
I had thought that the terms rake, clearance, etc., had to do with the angle of the various faces relative to the work. So, for example, I can create a cutter with no rake and no clearance by taking a squared off HSS blank and bringing the sides only to a point like an old steam ship's bow (this old beauty comes to mind: http://lighthouseantiques.net/photos/27295.jpg), and by placing it in the proper holder angled down, achieve both negative rake and clearance. If that is so then the concept of rake and clearance in carbide is one of intent of design, perhaps to warrant tool life, given that we can put any cutter at any angle relative to the work to produce desired rack or clearance, and sometimes both. I guess that's a long way of saying I thought the angle of the tool holder mattered in establishing rake, etc., and that the machinist would consider the vendor's guidelines as to what the range of operation is. I think, in fact, that is exactly what you have done with your cermet cutters, no?

This of course can be a completely misguided newbie misunderstanding :)

J Tiers
07-12-2009, 08:52 PM
Ummmmmmmmmm......

Well.......... I was talking about the original issue, not the semantics and whatever one.......

Seems that if you use carbide or other hard material inserts, at speeds which are appropriate, with depths of cut which are appropriate for the insert, you should not be surprised to get good results.

The argument about carbide seems to be that "you can't DO that with your little hobby lathe, so you are doomed to run them with slow speeds and tiny nibbling cuts for which they are not suited."

However, once you DO run the inserts at speeds etc that they like, the issue of"you can't do that" is negated, since you DID do that.

At that point the machine is by definition sufficiently powerful, rigid, or whatever to do the work. Therefore arguments to the contrary are obviously futile and somewhat stupid.

Since you did use the inserts more or less within their "good zone", it is no surprise that they worked.

I am somewhat surprised that an old and presumably flatbelt S-B would run that speed with a DOC of 0.020, but if it does, it does. Usually the flatbelt won't transmit more than a fraction of the motor power, generally the belt speed is too low and the belt slips long before the motor bogs down.

Evan
07-12-2009, 10:12 PM
Serpentine belt with belt dressing. It will stall the motor.

Evan
07-12-2009, 10:17 PM
I guess that's a long way of saying I thought the angle of the tool holder mattered in establishing rake, etc., and that the machinist would consider the vendor's guidelines as to what the range of operation is.

Then why does the ANSI nomenclature system contain information to identify the rake angle of inserts? Conversely the ANSI specs for tool holders do not contain rake information. How you choose to hold it is up to you but when I am buying inserts frequently the only information I have to go on is the ANSI spec in the type number.

lazlo
07-12-2009, 10:18 PM
I had thought that the terms rake, clearance, etc., had to do with the angle of the various faces relative to the work.

by placing it in the proper holder angled down, achieve both negative rake and clearance.

That's exactly right Dennis. Negative rake inserts don't have negative rake -- they have square sides. They're designed so the toolholder tips the pocket down 5 or 10° to give you the negative rake.

Positive rake inserts actually have 3 - 30° positive rake, so if you're making your own toolholder, you have much less latitude in changing the rake angles than a negative rake insert.


If that is so then the concept of rake and clearance in carbide is one of intent of design,

I thought the angle of the tool holder mattered in establishing rake, etc., and that the machinist would consider the vendor's guidelines as to what the range of operation is. I think, in fact, that is exactly what you have done with your cermet cutters, no?

Exactly. A flat-topped negative rake insert like the SNGA Evan is using is a worst-case scenario for horsepower and rigidity. But take that same negative rake insert with a positive rake chipbreaker, and you end up with a "Negative/Positive" insert that requires much less power and rigidity:

Metal cutting theory and practice, David A. Stephenson

http://i164.photobucket.com/albums/u15/rtgeorge_album/negativerake.jpg

lazlo
07-12-2009, 10:30 PM
Then why does the ANSI nomenclature system contain information to identify the rake angle of inserts? Conversely the ANSI specs for tool holders do not contain rake information.

The ANSI/ISO designations do specify the toolholder rake angles. The TNMG negative rake insert, for example, is intended to be used with the "MTGNR-XXX" toolholder:
"M" is clamp and pin, "T" for triangular insert, "G" for offset pocket with no additional relief, "N" for negative rake insert, "R" for right-handed tool:

http://i164.photobucket.com/albums/u15/rtgeorge_album/ansitoolholders.jpg

lazlo
07-12-2009, 10:47 PM
But a small point, and I'm sure you are aware, but others may not be. That 3rd position is actually "tollerance". "M" is not "Molded", and "G" is not "Ground", though it works out that way often enough that it's a decent mnemonic.

Reference Chart (http://www.carbidedepot.com/formulas-insert-d.htm)

Yeah, I know that's confusing. The tolerance actually indicates whether the insert is ground or molded. With a molded insert, the carbide is sintered in the actual insert mold, so the "M" tolerance is 2 - 5 thou.

A ground insert is sintered oversize, and ground to final dimension, so the "G" tolerance is 1 thou. In fact, this book is a little dated -- Sandvik spec's a tolerance of 5 tenths for their ground inserts. Also, the text doesn't mention this, but as Glenn was implying, the ground inserts are sharper, and cut nicer, but they're more expensive:

http://i164.photobucket.com/albums/u15/rtgeorge_album/tolerance.jpg

lane
07-12-2009, 10:51 PM
If you can turn the insert up side down and use the bottom side it is a negative rake insert. Period . Lay a square on top and if the edges are 90º it is considered a negative rack insert.Period again.

lazlo
07-12-2009, 10:54 PM
If you can turn the insert up side down and use the bottom side it is a negative rake insert. Period .

Agreed :D Negative rake inserts have square sides, period.


Note that these are all negative rake inserts:

http://www.plastools.com/insert3.gif

That's a huge advantage for the HSM'er -- because negative rake inserts have square sides, they can be flipped over, and you get twice the number of cutting edges.

You can't do that with positive rake inserts, because they have the positive rake angle molded or ground into the insert itself.

Evan
07-12-2009, 11:00 PM
The figure you posted is refering to negative/positive tooling as an insert with a negative side rake. Side rake is altogether different than back rake as it describes the plane of the top of the tool and it's relationship to the long axis of the lathe. If the tool is tilted down on the side toward which it moves as it cuts it has negative side rake regardless of the top rake angle or the cutting edge angle.

I wrote: "Conversely the ANSI specs for tool holders do not contain rake information. " I said nothing about clearance information which is a different matter. The clearance of an insert does NOT reflect the cutting top rake angle it provides.

N does not stand for negative, only insert relief angle provided. The tool holder clearance angle provides no information about tool top rake angle since that is dependent on the tool top surface features. Further, that clearance angle only applies to inserts with no clearance.

It would make no sense to specify both a clearance angle for the insert, which is the case, and another separate clearance angle for the tool holder. One or the other provides the required clearance, not both. In the case of inserts with no clearance then the tool holder provides the clearance. In the case of inserts with clearance then the insert provides the clearance and there is no specification for tool holder angle.

BadDog
07-12-2009, 11:14 PM
Yeah, I know that's confusing. The tolerance actually indicates whether the insert is ground or molded. With a molded insert, the carbide is sintered in the actual insert mold, so the "M" tolerance is 2 - 5 thou.

I agree that it works out that way, and I've read it in more than one "reference", but I just don't buy it.

If M is Molded and G is Ground, what are A, C, E, F, ... and all the rest? Just arbitrary aberrations with no meaning? I can't prove one way or the other, but I expect it is just a convenient mnemonic that became adopted fact by virtue of common application. It shows up in conversational texts, but never on official standard/spec sheets as far as I've seen. Or maybe it's the reverese. Those were common tollerances for the process, so adopted into the standards, and then expanded with others for better definition. But even if so, it still eliminates the original association as far as I'm concerned. For instance, I would expect an "F" to also be Ground, but that does not imiply it's really a G, and so on...

This is much the same as P in the second position. Folks will say that it means "Positive", but it's really just clearance angle, and there are "positive" inserts that use other designations (and that's as close to that discussion as I care to get! :D)

So if a molded insert process (or selection standard) produced inserts that met the spec for "G", I would expect them to label it "G". That's my story and I'm sticking to it... at least for the moment... :p

lazlo
07-12-2009, 11:22 PM
If M is Molded and G is Ground, what are A, C, E, F, ... and all the rest? Just arbitrary aberrations with no meaning?

And if a molded insert process (or selection standard) produced inserts that met the spec for "G", I would expect them to label it "G". That's my story and I'm sticking to it... at least for the moment... :p

Hey, I didn't make this stuff up, I'm just reading the spec. Believe me, I've read far worse ANSI/ISO specs. In fact, based on your profession, I bet you have too Russ ;)

If you look at the tolerances, "M" and "U" have the worst tolerances -- 2 - 5 thou. All the other letters are "G" (ground :) ) tolerance or better. If you look at the "A" tolerance -- that's 2 tenths. So I bet there's a Godlike Swiss TNAG-xxx insert out there somewhere that's ground to 2 tenths...

lazlo
07-12-2009, 11:30 PM
This is much the same as P in the second position. Folks will say that it means "Positive", but it's really just clearance angle, and there are "positive" inserts that use other designations (and that's as close to that discussion as I care to get! :D)

It's actually not a coincidence that negative rake inserts have an "N" designation. "P" was chosen for "Positive Rake" because it's the 11° positive insert, and for the first 20 years that carbide inserts were available, most of them were either N or P inserts (TPG's, etc).

So if you look at the relief angle table, there's "N", and "P", and the remaining slots are A - G. It's pretty obvious that they reserved N and P for the common Negative and Positive designations:

http://i164.photobucket.com/albums/u15/rtgeorge_album/relief.jpg

BadDog
07-12-2009, 11:54 PM
Hey, I didn't make this stuff up, I'm just reading the spec. Believe me, I've read far worse ANSI/ISO specs. In fact, based on your profession, I bet you have too Russ ;)

LOL! That's the truth!

Ageed in general.

As I've said, I've read some of the same references stating things just as you describe. But I maintain it's useless except as a mnemonic because there are ground inserts that are not G, and molded that are not M. Someone probably said something to the effect if "In the beginning there were molded and ground inserts, and their tolerances were typically of this value, so we'll use 'M' and 'G' to denote that value for coherency (folks that write specs like words like that ;)), and add in all the rest to fill out the field..." But regardless of the origins, I don't think you can really say "G is ground and M is molded". <shrug> Doesn't matter, too many "references" out there use this descriptions, and my pedantics aside, really doesn't matter to me either way. At least now folks who didn't know otherwise may register that there are other options beyond M and G, and so not be too surprised if/when they see them. Likewise for "P", though N is pretty clear cut and final...

Man, I wish it would cool down a bit. I got things I want to do in the shop. Suns been down a while, and it's just now dropped to 109...

lazlo
07-13-2009, 12:07 AM
But I maintain it's useless except as a mnemonic because there are ground inserts that are not G, and molded that are not M.

I agree the forward case is correct -- G's are not the only ground inserts, but every "M" insert I've ever bought was molded, and not as sharp as a ground insert.

I've also found that coated inserts are not as sharp as un-coated -- they grind first then PVD/CVD coat, and the coating rounds off the cutting edges. Which is, I think, why the "Upsharp" or "Honed" inserts are almost always uncoated.


Man, I wish it would cool down a bit. I got things I want to do in the shop. Suns been down a while, and it's just now dropped to 109...

We feel your pain down in Austin. For reasons I don't entirely understand, there's been a high-pressure zone that's been sitting on Central Texas, and we've had 105 - 107° for the last 5 weeks straight. That's 15° over our normal June/July temperatures, which is scary, because the temperature here peaks at the end of August...

dp
07-13-2009, 12:10 AM
Agreed :D Negative rake inserts have square sides, period.

So the TNMP insert in your image has 10 degrees rake relative to what? That "what" is the assumption the plane of the insert will be be in parallel to a ray depending from the center of the chuck when the insert is centered vertically on the work - tangent, as it were. In line with the cross feed, in fact.

So if the tool holder were dipped down 15 degrees and the tip brought to the tangent point again, that would produce a negative rake of 5 degrees and a rather stunning clearance angle. That may or may not be inside the design scope of the insert - particularly a sintered insert, logic tells me. At some point the shear forces against such configurations have to take a toll. While this is a possible configuration and will provide a chip breaker function, it seems to me there is a better way to achieve this.

If this is so then all the angles in practice come down to "it depends". In theory it seems easily defined except that I see no specification for tool holder expectations or I'm looking at the forest and seeing nothing but trees.

I use TNMP's all the time on my little Asian lathe and like the results. I typically cut 1018 and at a wide range of feeds and speeds owing to the curse of change gears and belts and a predisposition to leave the gears where they are for the final op (often threading), and hand feed the roughing passes. And I could get them at Boeing surplus for about $0.25 each.

Glenn Wegman
07-13-2009, 12:18 AM
and for the first 20 years that carbide inserts were available, most of them were either N or P inserts (TPG's, etc).


I was going to go there strictly as a guess in regards to the M (molded) G (ground) issue as it seems like a lot of coincidence that from the entire alphabet they chose P,N and M,G.

But I didn't! (well I guess I did):)

lazlo
07-13-2009, 12:33 AM
So the TNMP insert in your image has 10 degrees rake relative to what?

The 10° is the chipbreaker angle. That angle is specified w.r.t. a flat top insert. Like all negative rake inserts, the sides are flat.


So if the tool holder were dipped down 15 degrees and the tip brought to the tangent point again, that would produce a negative rake of 5 degrees and a rather stunning clearance angle.

Exactly. You have a square-sided negative rake insert, and you have either no chipbreaker, like Evan's insert, or a variety of chipbreakers than range up to 20° (if I remember correctly). So a HSM'er can change the pocket angle to trade-off the rake and clearance angles.

That image is from the Plastools web page, which makes insert holders for home-shop machinists. So they set the pocket much more positive than you would for an industrial machine.

The ISO toolholders (i.e., the standard toolholder you buy at MSC or Enco), have specific pocket angles. The MTGNR toolholder I mentioned earlier, which is the toolholder that goes with the TNM* inserts, is something like 5° negative front and side:

https://www.greenleafglobalsupport.com/wcsstore/Greenleaf/images/catalog/product/t_aibbc_trng_neg_mtgn.gif

In other words, whether you buy an ANSI/ISO toolholder from Hertel, or Sandvik, or Valenite or Bison/TMX, they all have the same insert pocket angles.

By the way, the same ANSI designations apply to boring bars. The only difference is the material is pre-pended to the designation. So a TNMG, TNMM, or TNMP insert uses an MTGNR-xxx toolholder, or an Axx-MTGNR boring bar. 'A' designates steel, 'C' is carbide.

Peter.
07-13-2009, 04:35 PM
Lazlo in the diagram above, looking at the holder in plan, which way does the pocket negative rake angle go? I need to make a holder for my TNMP inserts which arrived today. My first guess is that the pocket rake would be (for instance) 5 degrees directly 'south' on the diagram to provide clearance along the cutting edge, but wouldn't this leave the forwardmost tip of the insert cutting tangentially and with no clearance at all, so I guess I need an amount of negative rake to the 'west' on the diagram too or it will chip-off the cutting edge on the other side of the insert?

Alistair Hosie
07-13-2009, 04:40 PM
As usual a lovely job well done Evan well done but are the chips meant to be so blue I thought that meant you were cutting too hot and needed to cut back a little ?Alistair

toastydeath
07-13-2009, 06:23 PM
As usual a lovely job well done Evan well done but are the chips meant to be so blue I thought that meant you were cutting too hot and needed to cut back a little ?Alistair

Carbide doesn't care about blue/purple (and even sometimes cherry red) chips; the only way to gauge the "right" temperature is to check the edge wear periodically. If it's wearing faster per minute than you want it to, then you need to back the speed down.

You can use the chip color as a rough guide on HSS because the temperature range where HSS really starts to break down fast is in the range where chip color has the most change. It's just a convenient coincidence.

J Tiers
07-13-2009, 11:34 PM
Hss seems to prefer no more than a brownish chip, not into the purple area. Actually, if you look up the temper colors, you can estimate the chip temp, but that may not reflect the cutting edge temperature.

While grades of HSS claim to work red hot, it seems generally to be a bad idea to push that.

As mentioned, carbide will take/make much hotter chips.

Curiously, the last time I had occasion to compare them, I was in fact getting blue chips with HSS, but too much edge wear on a cutter with considerable side rake. When the chips were colder, I was getting cobwebs waiting for each pass.

When I switched to carbide, at first via a TNMG insert, and then later via an older USA-made brazed cutter with neutral rake, I got much colder chips at a similar DOC and speed/feed to that which had produced the blue chips with HSS.

Glenn Wegman
07-14-2009, 08:59 AM
The issue is one about insert nomenclature. It seems that the ANSI nomenclature for insert designation is meaningless. It is being argued that the rake of the cutting edge relative to the work does not determine the insert type as per ANSI nomenclature. In actual fact it does although apparently you may need to buy what is being called a negative insert in order to get a positive one. Proper interpretation of the ANSI labeling system does reveal the type of insert which is of course the objective of a standard.

The argument posed by Robert results in the rather awkward circumstance of specifiying a negative rake insert to obtain one with a positive rake cutting edge. He has also made some statements that are flat out incorrect, such as that the second letter of the insert identification system indicates the rake angle of the cutter when in fact it only specifies the clearance angle below the cutting edge.

I was just browsing the Korloy catalog and throughout the catalog inserts are classified by two catagories, positive and negative, regardless of chip breaker configuration.

http://img.photobucket.com/albums/v647/Fighter1/korloy.jpg

lazlo
07-14-2009, 01:02 PM
I was just browsing the Korloy catalog and throughout the catalog inserts are classified by two catagories, positive and negative, regardless of chip breaker configuration.

All tool catalogs, and any modern machine shop text, including the half dozen or so I posted (and confirmed by Lane) say the same thing: xNxx inserts, with square sides, are negative regardless of the chipbreaker. So the Koroloy catalog, like the Sandvik, Kennametal, and Valenite catalogs, indentify CNxx, TNxx, SNxx, et al as negative inserts.

A hybrid insert like the TNMP or CNMP is referred to as a "Negative rake insert with a positive chipbreaker" or a "Negative/Positive insert."

So as this picture from Metal cutting theory and practice shows, the toolholder and insert orientation with respect to the workpiece is negative, regardless of the chipbreaker. If you use a flat-top negative insert ( a "Negative/Negative" insert), it's purely negative. But replace that insert in the same toolholder, with the same pocket angles, with one with a positive chipbreaker (a "Negative/Positive" insert), and you have a negative insert angle with a positive shear angle -- the best of both worlds:

http://i164.photobucket.com/albums/u15/rtgeorge_album/negativerake.jpg

noah katz
07-18-2009, 03:55 PM
"For our HLV clone, I use very positive (20-35 degrees of positive rake) stainless steel finishing inserts from Sandvik that have a long (~.4") cutting edge and are capable of deep cuts. They work brilliantly on just about everything."

Doesn't that make the insert fragile? Do you mean everything as long as it's finishing cuts?

It's great to be able to economize by being able to flip the insert over, but what about the cost of toolholders for these?

Can they be used in a standard toolholder for BX toolpost with no rake?

Would a standard zero front rake toolholder work as long as the cutting edge is at centerline height or slightly below?

Evan
07-18-2009, 08:06 PM
You still don't have it right Robert. An insert cannot have a negative and positive back rake at the same time regardless of the chipbreaker style or how the tool is tilted toward the work. That isn't what negative/positive means. Your diagram explains that.

In order for an insert to be considered "negative/positive" it must be cutting with negative SIDE RAKE. Negative rake on the tool holder toward the work is irrelevant if the cutting edge is still positive. Kyocera lists side rake separately from back rake (top rake) or insert holder inclination (not negative rake).

See below.

http://ixian.ca/pics6/insert8.jpg

Glenn Wegman
07-18-2009, 11:03 PM
5.5" bushings turned from 36RC 4140 turned at 900 fpm using Cermets. (Turned in pairs, back to back on a manual lathe)

http://img.photobucket.com/albums/v647/Fighter1/Bushing.jpg

http://img.photobucket.com/albums/v647/Fighter1/PC260901.jpg

lazlo
07-18-2009, 11:41 PM
http://i164.photobucket.com/albums/u15/rtgeorge_album/Evan.jpg

Evan, Side Rake Angle is the angle of the top of the tool, with respect to the side. In other words, it's the angle the top of the tool (the positive chipbreaker) is sloping backwards:

http://i164.photobucket.com/albums/u15/rtgeorge_album/Tool_Bit_Geometry.jpg

lazlo
07-18-2009, 11:58 PM
You still don't have it right Robert.
An insert cannot have a negative and positive back rake at the same time regardless of the chipbreaker style or how the tool is tilted toward the work.

Sigh. One last time. From Moltrecht:

"The relief angle on the negative rake insert, shown at B, is provided by the inclination at which the insert is held on the tool holder. Held in this position, the flanks of the insert can be perpendicular with both faces and all of the edges on both faces can be used as cutting edges. Therefore, negtive rake inserts have twice as many cutting edges as comparable positive rake inserts. Another advantage of negative rake inserts is that they are stronger than positive rake inserts and more able to withstand shock loads, such as encountered when taking interrupted cuts. The advantage of positive rake inserts is that when cutting, the cutting force is significantly less. When the cutting force must be kept low as possible, as when cutting thin material sections, a positive rake insert should be used.

Positive-Negative rake inserts, view C, are held on negative rake tool holder but have an effective positive rake angle, provided by the groove on the face of the insert."


http://i164.photobucket.com/albums/u15/rtgeorge_album/Moltrecht.jpg

And open any tool catalog, and it's exactly as Moltrecht and the other machinist texts I've posted describe:

http://i164.photobucket.com/albums/u15/rtgeorge_album/CNMP.jpg

Evan
07-18-2009, 11:59 PM
That's right (post 103) and it has nothing to do with the top rake (aka back rake) or the inclination of the tool holder toward the work. My illustration shows negative side rake in which the cutting edge on the SIDE is negative in respect of the work. That is the "negative" in "negative/ positive", not the fact that the insert may be tilted by the tool holder toward the work, which is how you have been explaining it all along. You can have a tool holder that has positive rake with respect to the work and negative side rake at the same time.

Tool holder inclination provides clearance while in the case of inserts with a chipbreaker feature that feature may provide a positive cutting edge. I grind HSS tools with negative side rake and positive back rake for boring. They take a heavy cut on the way in which deflects the tool but on the way out it is cutting positive/positive and takes a fine cut which compensates the spring.

Look at Kyocera tool holders. They don't call the tilt of the tool holder "rake". It's the inclination angle. They list side rake seperately which is the negative in negative/positive. Your diagram above in post 104 is incorrect.

http://global.kyocera.com/prdct/tool/pdf/catalog_cp231.pdf

nheng
07-19-2009, 09:06 AM
Although I skipped 102 replies, I can see Robert's and Evan's points.

In Stephenson and Agapiou's "Metal Cutting Theory ..." book here:

http://books.google.com/books?id=19AdVu1O4fQC&pg=PA172&lpg=PA172&dq=%22negative-positive%22+rake&source=bl&ots=A8eQ4rZXYd&sig=JT9ouDLGVo6AK7zm5TaYd2XYH84&hl=en&ei=jQljSpeOBZSStgf-wKWyAg&sa=X&oi=book_result&ct=result&resnum=4

They refer to negative/positive inserts as negative side rake, positive back rake. Robert's illustration is also correct, showing a negative back rake insert that has become positive due to the chipbreaker.

So, it seems to be a simple matter of the same name (sort of) having been used for two different things in the same industry. Not a big surprise. Guess you gotta read the fine print before plunking down $10 - $20 per insert :)

I've had major headaches in electronics dealing with printed circuit board (PCB) manufacturers. Here's an industry that is quite mature yet 3 major suppliers across the country do not agree on the definitions of a number of common fab options :(

Den

Evan
07-19-2009, 10:02 AM
The ANSI specs refer to the side rake as the negative rake as refered to in the definition being used to identify a negative/positive insert. The confusion arises because a negative rake insert also has no clearance and so must be inclined toward the work (tool holder inclination) to provide clearance.

In the tool holder I made to use the insert in my original post I provided about 7 degrees of forward inclination and the same -7 degrees side rake. Because the top rake is negative and the side rake is negative it is a negative/negative insert.

It isn't a matter of different manufacturers using a different definition since if they ignore the side rake then they only have one rake to talk about, the cutting edge. Inclination provides clearance, the shape of the cutting edge determines the top rake angle. Those are two different things. To refer to the forward inclination as the negative in negative/positive is a paradox and an oxymoron. It must be one or the other. This is the point I have been making all along. The insert has either a positive edge, a neutral edge or a negative edge. By convention a neutral edge is considered negative, a bit like a temperature of -0.

What makes an insert with a positive rake edge a negative insert isn't the fact it is inclined to provide clearance. It's the fact that the top plane of the insert is inclined toward the chuck.

lazlo
07-19-2009, 10:12 AM
In Stephenson and Agapiou's "Metal Cutting Theory ..." book here:

http://books.google.com/books?id=19AdVu1O4fQC&pg=PA172&lpg=PA172&dq=%22negative-positive%22+rake&source=bl&ots=A8eQ4rZXYd&sig=JT9ouDLGVo6AK7zm5TaYd2XYH84&hl=en&ei=jQljSpeOBZSStgf-wKWyAg&sa=X&oi=book_result&ct=result&resnum=4

They refer to negative/positive inserts as negative side rake, positive back rake. Robert's illustration is also correct, showing a negative back rake insert that has become positive due to the chipbreaker.

...and as I explained 102 posts back, flat-topped negative rake inserts with purely negative shear angles are not well-suited to a Home Shop Machinist -- they require maximal power and rigidity.

Get the same negative rake insert Evan used, but with a positive chipbreaker -- the Negative/Positive insert in Figure C in the page I posted from Moltrecht -- it will require much less horsepower and rigidity than the exact same negative insert with a flat top, in the same toolholder.

Evan
07-19-2009, 10:23 AM
flat-topped negative rake inserts with purely negative shear angles are not well-suited to a Home Shop Machinist -- they require maximal power and rigidity.



The entire point of this post is to show that isn't true. The results prove it.

http://ixian.ca/pics6/insert1.jpg

lazlo
07-19-2009, 10:31 AM
The entire point of this post is to show that isn't true. The results prove it.

If you use a more modern negative rake insert with a positive chipbreaker, you wouldn't have to baby it:


I applied this to the job running the lathe at 800 rpm and taking light cuts of no more than .020" and less for the finish pass.

Glenn Wegman
07-19-2009, 10:43 AM
Look at Kyocera tool holders. They don't call the tilt of the tool holder "rake". It's the inclination angle. They list side rake seperately which is the negative in negative/positive. Your diagram above in post 104 is incorrect.

http://global.kyocera.com/prdct/tool/pdf/catalog_cp231.pdf

Evan,

Can you post an example that is shown in the catalog of a negative/positive tool in accordance with your definition?

According to your definition, it would have negative inclination with positive side rake.

loose nut
07-19-2009, 11:25 AM
Got to interrupt the snipping here with a basic question.

The original post was the effect of tooling on SMALL lathes. What determines what a small lathe is as far as carbide type tooling goes.

Mine is a common type Chinese 13 x 40 Light industrial (which means that it is to light for real industrial work) that is available from all the suppliers.
To me it is a big lathe at least compared to the 9 x 20 and other smaller types that many are using but to the machinists at work it is a "little" lathe.

I use TMNG inserts with good results but at what point should a person consider not using carbide etc. When does a lathe become to small for them or what type or inserts don't work well with the smaller less rigid type of lathe some of use.

I guess more to the point what style of tool should we avoid.

OK, resume combat operations.

lakeside53
07-19-2009, 11:56 AM
Hmmm... I guess it depends on the overall rigidity/power of the lathe... which often follows size, but not always.

When I first set up my Emco, every expert told me that carbide was a bad choice. Well.. you're wrong:D It's a 10x24 (?) V10P with a 1hp motor, I use quality positive rake carbide almost all the time, and although it took a while to figure out what really did work, I now get good results. I try it on my neighbors 9x20 Jet (it was mine...), and it's not very happy. At the other end of "my scale", I have a massively rigid (for that size of lathe) 4hp 14x40 Polamco that runs CXA sized tool post and carbide - in a few days I'll power it up again and get to compare :) The only test I did was pre-purchase, and it pealed off a dark blue spring of 4140 like butter.

Boucher
07-19-2009, 12:24 PM
Post # 112 Loose Nut said "I use TMNG inserts with good results " Did you mean TNMG? I am having a hard time keeping this straight.

Earlier Lazlo said:
"I like TNMP and CNMP negative rake with positive rake chip breaker."
Glen Wegman said:
"If you like those you will really like TNGP and CNGP."

He is right I ordered some and they are in and they look great.

Now if I can produce something that has the surface finish anywhere near what Evan's original post demonstrated I will be very pleased.

This thread has also inspired me to make some of my own tool holders.

This thread also inspired me to enroll in Sandvik's Online training course.

lazlo
07-19-2009, 12:38 PM
Post # 112 Loose Nut said "I use TMNG inserts with good results " Did you mean TNMG? I am having a hard time keeping this straight.

Earlier Lazlo said:
"I like TNMP and CNMP negative rake with positive rake chip breaker."

The difference between the TNMP/CNMP and the TNMG/CNMG inserts is that the latter has the flat land in front of the chipbreaker. That greatly improves the edge strength, but then you have to make sure you take a big enough DOC to get past the flat land to the positive rake provided by the chipbreaker. If you don't take a big enough cut, the TNMG/CNMG effectively has a flat top, with a negative shear angle (because the whole insert it tilted down with a negative rake orientation w.r.t. the workpiece).

That's why I prefer the TNMP/CNMP -- unless I'm taking an interrupted cut, I don't need the edge strength of the flat land, and I'd rather not worry about DOC:

http://www.plastools.com/insert3.gif



This thread also inspired me to enroll in Sandvik's Online training course.

The Sandvik course is great. If you sign-up online, they'll also send you their "Metalcutting Technical Guide": a great hardcover textbook which covers all this material, and much, much more, with gorgeous illustrations...

J Tiers
07-19-2009, 12:57 PM
I think some of the point (maybe ALL of the point?) has become obscured in details many of which are of course useful......


Evan used a Cermet insert, and if I read/understand correctly, he used it at the specified negative rake orientation, and at a speed correct for the material, about 3 x the HSS speed.

He is doing that on an SB 9" machine, certainly NOT the most powerful and figid machine available, even in that size range.

And it works.

IIRC, it was with 1018, which is notorious for bad torn finishes.

Evan: have you run any 4140/4140 PH or similar? I found that to require even more power, and I am wondering if you can still get that sort of finish with it.

BobWarfield
07-19-2009, 02:41 PM
The ANSI standard differs with a lot of what the catalog charts have to say:

http://www.ccpa.org/pdf/B212_4.pdf

The catalogs and the posters here attribute a lot more to those 4 letters in an insert designation than I can read into that spec which seems a lot more related to making sure inserts are interchangeable with their holders than anything else.

For all the pages here, there are really very few points being made that matter for making chips:

1. Positive rake requires less cutting force and is generally better for lighter machines. In fact, positive rakes are taking over from negative even for heavier machines in many cases because the geometry cuts better. You can see that reading through the PM board to see what those guys use/recommend. Negative rake is principally useful for durability, but as the positives get better at interrupted and other "difficult" conditions, why bother with negative?

2. The meaning of the various letters in an insert designation is pretty prosaic. Some things we can determine from it but most we can't. We don't know the rake unless we factor in the toolholder and the top surface of the insert. Those two are actually not called out very well by ANSI. Therefore, we have to understand our toolholders and the meaning of positive rake and visualize what will happen with a particular insert. Those "sharp" inserts are clearly very much going to have positive rake. Many other inserts it isn't so clear.

3. Since you can't really tell from just the 4 ANSI letters what's going on, you'd better have one or more of the following in hand before buying the insert (unless you just want to experiment):

- Full ID on the insert so you can go consult the manufacturer's catalogs. This is often hard on eBay.

- A big picture of the insert and enough practical knowledge (more than enough in this thread) to guess how it will cut.

- A solid recommendation for the insert from someone doing similar work on a similar machine.

- Help from a rep picking out your inserts. Clearly YMMV depending on how good the rep is. This is why peeps like the "Exkenna" guy over on PM so much, or Frank Mari. Their advice has prooved out.

Everything else is a crapshoot and can be extremely frustrating.

Just as an example, not long ago the CCGT inserts were the ticket for smaller lathes. Peeps thought the "G" meant "Sharp", but it was only the tolerance. It wasn't long before manufacturers were selling "G"'s that weren't sharp because there was demand to pay the higher price. Then I started seeing CCMT's that were Sharp. The whole ANSI business ceased being a useful determiner of anything other than whether the insert would fit my toolholders. Hence the 4 criteria above.

4. The idea of a lathe "too lightweight" for carbide is an interesting one. A small Southbend will clearly handle carbide. My Lathemaster 9x30 does too. The ubiquitous 9x20 is noticeably less rigid than these, but with the common mods, seems like it would work. What then is "too lightweight"? Unimats? 7x14's?

For the hobbyist, carbide is a matter of personal taste more than anything. Do you want to spend your time trying to understand the minutiae of insert selection (feels like stamp collecting sometimes), or grinding HSS tools? Either takes away from making chips, but I like my carbides though I also do some HSS.

Last point:

Be careful if you have an indexable tooling fetish as I do not to accumulate tools that use too many different insert types, or inserts of exotic design. It's just too hard to keep up with it all. Hence all my mill tooling uses APKT (or equivalent) and all my lathe tooling except the boring bars and parting tool uses CCMT.

Apparently cheap toolholders look like such a deal until you're paying $10 and up per insert on a facemill with 7 inserts. Ouch!

Cheers,

BW

Evan
07-19-2009, 03:16 PM
Can you post an example that is shown in the catalog of a negative/positive tool in accordance with your definition?

According to your definition, it would have negative inclination with positive side rake.


No, it would have negative side rake and positive top rake at the cutting edge. It's the orientation of the cutting edge relative to the work that determines top rake actual value (aka back rake), not inclination. The amount of inclination (clearance angle) is specified by the second letter in the ANSI code. Of course the inclination plays a part in the total value of top rake but it isn't specified by the ANSI code in conjunction with a value for the insert that allows one to calculate the top rake. Inserts are only identified as to whether they are negative, neutral or positive at the cutting edge with the inclination included. That's the 4th letter of the code.



If you use a more modern negative rake insert with a positive chipbreaker, you wouldn't have to baby it:


I didn't try heavier cuts because I didn't want to remove much material. I have since used heavier cuts and it does alright. It doesn't seem to require noticably more power than the other cutters I use. I run carbide most of the time and I sharpen it to slightly positive for most things. I make most of my own tooling including carbide tools and even carbide milling cutters. I will show an example of a carbide mill cutter soon.

lazlo
07-19-2009, 03:46 PM
Just as an example, not long ago the CCGT inserts were the ticket for smaller lathes. Peeps thought the "G" meant "Sharp", but it was only the tolerance. It wasn't long before manufacturers were selling "G"'s that weren't sharp because there was demand to pay the higher price. Then I started seeing CCMT's that were Sharp.

I think the confusion here stems from the up-sharp aluminum inserts: the up-sharp and/or honed inserts use proprietary (i.e., non-ISO) suffixes: -F, -U, -AS, -HP, -1L. Upsharp inserts are ground inserts that have gone through a further edge honing process, so upsharp inserts are only available on ground inserts (i.e., not molded CCMT's).

The upsharp high-positive inserts have very fragile edges, and are described by the manufacturer as being relegated to fine finishing cuts on aluminum. They were never made, or intended, for hobbyists, so it would be hard to fathom the insert vendors changing designations for a small handful of people :)


The tolerance actually indicates whether the insert is ground or molded. With a molded insert, the carbide is sintered in the actual insert mold, so the "M" tolerance is 2 - 5 thou.

A ground insert is sintered oversize, and ground to final dimension, so the "G" tolerance is 1 thou. In fact, this book is a little dated -- Sandvik spec's a tolerance of 5 tenths for their ground inserts. Also, the text doesn't mention this, but as Glenn was implying, the ground inserts are sharper, and cut nicer, but they're more expensive:

http://i164.photobucket.com/albums/u15/rtgeorge_album/tolerance.jpg

dp
07-19-2009, 04:21 PM
Since I'm now quite puzzled over all of this, is there any dispute that the above tnmp insert with 10º positive rake shown is now negative 5º rake in the image below? The difference is the tool holder has rotated the insert 15º and increased the clearance angle by 15º.

http://thevirtualbarandgrill.com/machinery/tnmp-5.jpg

Peter.
07-19-2009, 04:34 PM
Yup that's a negative negative negative insert :)

lazlo
07-19-2009, 05:08 PM
Yup that's a negative negative negative insert :)

Well said! :)

loose nut
07-20-2009, 07:41 PM
Post # 112 Loose Nut said "I use TMNG inserts with good results " Did you mean TNMG? I am having a hard time keeping this straight.



Sorry, my bad, typo.