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Robert Burch
11-20-2001, 11:13 AM
I notice that my lathe tool holders are angled up at 7.5 deg for use with HSS tool bits. Holders for carbide tool bits don't seem to have any up angle. All the carbide tool bits I've seen have flat tops (I am not sure about carbide inserts). Do carbide bits operate with no top rake angle? Can anyone shed some light on this for me?

SGW
11-20-2001, 03:28 PM
Right -- because carbide is so brittle, it has to have very little clearance angle so the edge remains well supported and doesn't chip.

That's why most home equipment can't make full use of carbide; carbide requires a lot of rigidity and a lot of power to drive what is a pretty blunt cutting edge. A HSS toolbit can be sharpened to a much keener edge than carbide and still hold up.

Actually, toolbits cut mostly on the left-hand side anyway (assuming you're feeding right to left); they don't really cut on the front, so I think the design of those angled "Armstrong" style toolholders is the result of a somewhat flawed notion of cutting geometry. Notice, for example, that the newer "Aloris" style toolholders don't have any angle, nor do any of the "4 in 1" toolposts I've seen.

snorman
11-20-2001, 05:42 PM
Some carbide tool bits have a bit of of side rake. Many toolholders for carbide inserts actually have negative rake (angled down) for heavy cuts on big lathes.

MarshSt
11-21-2001, 12:01 AM
The negative rake on the inserts lets you use double sided inserts also, 6 edges instead of 3. I think it makes a stronger insert since the support for the cutting edge doesn't taper back. The top of most carbide inserts have some sort of chip breaker profile built in, make beautiful 9 chips when you get the feed set up just right. We used neg. rake holders, I think about 2 degrees, on all of our machines, even when we ran ceramic. They don't do too well on real small cuts unless they have a really small nose radius.We never set up pos. rake holders to compare the 2 on the same machine, would have been an interesting experiment though.

Steve

Thrud
11-21-2001, 03:02 AM
Gents,

The negative rake carbide inserts are used for really tough stuff - like finish turning hardened crankshafts to size instead of grinding using CBN inserts.

If you check Sandvik Coromants "Modern Metal Cutting" handbook it shows in detail what happens with different "rake" cutting tools. What we call "cutting" action is just forcing a wedge into a substance until there is failure of the material at the "shearline"

Negative inserts create higher temps at the insert which help to soften the metal at the shearline. Negative rake requires the highest ridgidity as the pile up of metal at the shearline tends to push the insert away with considerable force.

Positive rake inserts cleave the shearline better (much like a cold chisel's cutting action) and has lower temps at the insert. To get those beautiful "6" (you are looking at them upside down, man!) ;-) or "9" chips the chip actually curls up towards the workpiece surface cut on the previous revolution and snaps off when it hits it. This requires a heavy feed for the chipbreakers to work - otherwise you get a very long, hot, stringy, (dangerous) chip from the cut - again this requires more power and a sturdy machine.

The side clearance angles are built in for different carbide inserts, or their supporting seats/toolholder account for it. Some are are adjustable for optimum performance in ops such as threading (when the thread is critical).

New tougher silcon whisker reinforced carbides are being developed for abusive use - interupted cuts / very low SFPM. Just what the HSM needs. These will be a few years yet...

If you want optimum performance from Non-carbide tooling use M-42 or T-15 bits. T-15 is really tough and is the best choice, but is tough to grind (use SiC, CBN, or Ceramic wheels).

Dave

Robert Burch
11-21-2001, 07:11 AM
Thanks to all of you who replied so quickly and thoroughly. You saved me many hours of digging. I have a 6" Atlas so I think I will stay with the HSS bits and use a positive rake. I have tried some Carbide bits with 0 deg rake and noticed the tool post doing a dance. You have explained the cause, I lack rigidity, (perhaps a common complaint among the senior members).
Anyway, every cut I make is a learning experience.

SGW
11-21-2001, 08:18 AM
Yeah, a 6" Atlas will do a lot better with HSS. Get yourself an adjustable angle protractor -- one of those simple jobs with the protractor head and pivoting arm -- to measure the toolbit angles. The proper angles matter, both for cutting action and longer tool life.

You may want to keep a carbide toolbit around for the occasional time when you run into a hard spot in a cast iron casting, but that's about the only time you'll need carbide, I think.

Robert Burch
11-21-2001, 05:34 PM
Funny you should mention keeping a few carbide bits around. That's exactly what got me thinking about it. I was turning some unknown and very hard stock and the HSS bit was just wearing away. I had to use carbide to cut it.

docn8as
11-21-2001, 06:57 PM
hi speed ,stoned edge ,plenty SIDE & back rake on steel & the cuts u can take on that6x18 will slip the belt before x/ceeding capacity of lathe......openside tool holders big help. 2x2x11/2 works fine....single, double or 4way.make a gib to slide in tool post &lock em down w/ 3/8 bolt /stud/nut..the angled slot allows setting on center w/ out shims (careful layout) .....lathe is more ridgid than one is led to beleive ....have taken .030 cut w/ 3/8 milling steel w/ atlas milling attach.w/ no shake/chatter... if u decide to make some , will send u a sketch......
best wishes
docn8as

docn8as
11-21-2001, 07:22 PM
forgot to mention

triangle shaped two slot blocks get into tight places w/out interference...cut slots for 1/4 in bits...u will end up w/ a dozen or so blocks if going this way......increased ridgidity of these blocks a big + .& can change tools w/ couple quick turns of nut off & on..almost as quick as $200 tooling..only caveat is cannot adjust bit extension because of angle( could shim but that defeats purpose of angle.)...have these on 6 and 12 crftsmns& wonder why it took me so long....much more ridgid & much quicker.....
best wishes
docn8as

Thrud
11-21-2001, 11:28 PM
Gents,

I use the negative insert stuff to cut nasty stuff, rusty-crusty scrap, welds, and hardened stuff like Centers or shanks.

Mondo fun. Hell, I even keep a load of steel bits about - you never know what you need next...;-)

Dave

Robert Burch
11-22-2001, 07:37 PM
docn8as
If you'd care to send info on tool block, how can I refuse the offer, e-mail to BurchRD@aol.com Thanks.

Thrud
I save my few carbide for the "hard" stuff, then if I cut thru the crust I change over to HSS. Thanks

spkrman15
11-23-2001, 08:24 PM
So if i was to weld up a piece of metal and i wanted to cut it down i would be better with a carbide tip?

Spkrman

snorman
11-23-2001, 09:03 PM
spkrman, welding usually results in hard spots that play hell with a steel tool. Sometimes it's all you can do to cut with carbide. Be prepared to resharpen the tool often; especially if you've got interrupted cuts.

Thrud
11-24-2001, 04:56 AM
spkrman15:

If you need to weld a peice up and machine it TIG is the best choice (and neatest/cleanest).

Annealing & stress relieving the piece is not a bad idea either before machining it.

When parts are built-up for machining, plasma coating is the best method of application especially with materials like Stellite (hard surfacing materials).

Dave

spkrman15
11-24-2001, 07:24 AM
Anneling and Stress releiving....how do i do that?

Spkrman

SGW
11-24-2001, 07:21 PM
For a first approximation: "heat to a dull red and cool slowly." The slower the better on the cooling. Heat the part and bury it in powdered wood ashes, for instance, and leave it. Some other insulating medium would work if you don't have a bucket of wood ashes, but that's the traditional way.

Thrud
11-25-2001, 03:23 AM
Hot sand is used when welding cast iron to let it cool slowly. You could preheat your sand in an oven to 450* and bury the part after getting it to the proper temp.

Warning: wife may kill you if she catches you messing with her oven! (bakin' up sand - Duh!)

Dave

Buy new sand in a bag - Don't use dirty sand. Silca dust pours like flour and would have less air space.

[This message has been edited by Thrud (edited 11-25-2001).]

spkrman15
11-25-2001, 09:30 PM
Ok i know about the cast iron technique. So after welding my best bet would be to heat up the part again and let it cool down in ashes. Got it. Doesn't that however take away the tempering that was done to the shaft? If i was re-cutting splines for example. Wouldn't i have to retreat the metal to harden it??

Spkrman

Thrud
11-26-2001, 12:44 AM
Depends on if they are hardened before welding or not. If they are too hard the shaft snaps (ask some Ford Direct Injection Diesel guys about their automatics) under use. Depends on where the weld is - it depends onlots of things.

spkrman15
11-26-2001, 05:18 PM
What i am woundering is if i weld up a shaft to repair some of the splines. I would have to anneal it by heating it until a light red glow and letting it cool down in ashes. Then do the turning and cutting of the splines. Then Case hardening it?

Are those the right steps??

Spkrman

docn8as
11-26-2001, 08:12 PM
if u want it hard ,....& if case hardened to begin with ....may have been through hardened & then drawn to a spec. hardness...may not need to be hardened.....if it is lo carbon steel,not c/hrdnd, &u dont throw a lot of carbon @ it w/ ur torch(carburizing flame ),it may not be too hard to machine.....wire welding techniques also control hardening, but i am still in the dark ages w/ torch /buzzbox...i will always remember welding a new bolt handle on a rifle & having it come off w/ first pull..point.?......dont use DRILL rod for handle.almost 50 yrs later ,still a bad memory...fortunately came off in my hand . not in customers, on safari looking @a charging water buffalo

best wishes
docn8as

Thrud
11-27-2001, 12:28 AM
Spkrman

I am correct is assuming the splines were stripped out or damaged? If this is so, I would either make a new shaft or a stub shaft that would be splined and then welded to the shaft afterwards.

I would make the stub long enough to avoid getting the weld in the way of a bearing or pillow block so you do not have to machine it after it is welded. It would be easier to use a peice of tubing to overlap the joint and thus align the shaft to the stub and then weld this "collar" to join the two peices.

I think this would be easier than trying to remachine splines in a built up weld area. A piece of 4130 can be hardened and has good impact resistance. 4140 hardens deeper but has lower impact resistance

If it is a high load / high horsepower part then make a new shaft and get it hardened the same as a axle shaft at a heat treating house.

Dave

Robert Burch
11-27-2001, 08:32 AM
docn8as

Regarding the welding of drill rod. Can it be tempered after welding? I once had some rigging pins welded up for me. They were made from drill rod. I dropped them onto the table and the welds shattered. I just assumed the welder quenched them in water and perhaps should have let them air cool.

halfnut
11-27-2001, 10:57 AM
How did we get from tool holders to welding techniques, follow the thread right.

I've got to add 2 cents to this end of the discussion.

If I have to build up a worn area I prefer to use 7018 stick if I think part is anything but mild steel, if I know it to be mild steel then I use 6013, 7014 or the wire feed if I am at work, haven't modernized that much at home. If part is hardenable material it is best to preheat before welding and stress relieve or anneal afterwards.

Problem with welding hardenable material is that the arc generates heat which raises the material being welded to it's hardening point, the mass of the material will cool metal surrounding weld enough that hardening takes place. One of the reasons that a part often breaks next to a weld, stress the other. Multiple pass welds negate this to an extent. As with hardening a piece of tool steel, if it isn't tempered it will break, this is the reason for stress relieving a part after welding. The preheat lessens the quenching effect. Combine the preheat with a stress relieving and one can weld even springs or drill rod.

But when welding alloyed steel, one can't expect things to be the same once it is welded, the welding rod probably won't be the same alloy as that of the parent metal, best you can do is to try to shoot for approximately the same tensile strenth as annealed. Anyone ever ran 10016 D-2 rod, mean stuff, think 7018 is sticky, this stuff is terrible.

TIG works great for little stuff, have used it with piano wire filler for a few jobs. Remember a guy using sewing needles for filler rod on one little bitty job one time, it worked.

Stress is what kills a lot of cast iron welding. Cast iron has very little or no ductility, we know that. When you strike an arc and deposite weld what happens, it immediately starts to cool, when it cools what happens, it starts to shrink, when it shrinks what happens. Something has to give, since cast iron won't give it breaks, right along side of the weld.

When welding cast iron nickle rod works well because that the Nickle rod is soft and maleable, as it cools one can peen it stretching it as it shrinks, negating this stress problem. Also the reason why to only weld short beads, got to peen before it starts to cool off.

Welding plain old steel is affected by stress also, reason not to use constrained joints if possible. Never finish up a bead in a stress point.

Tool holder angles, that's what we were talking about, yes the Armstrong holders had back angle, was there for a reason. Made for easier ground tools, didn't have to grind as much back rake into tools, already some there. Takes just a few minutes to grind up a plowing tool for an armstrong type holder that will move a lot of material with mininum horsepower.