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Abner
11-28-2010, 05:32 PM
Newbie question
I have a SB 10 with a 4" sq. turret tool holder.
What I want to do is hold 3/8" sq. HSS tool bits.
Watching Tubal Cain on youtube he shows how to grind bits and mentions that the tool holder gives you a 16 deg. backrake.

My turret tool holder is to short to accept the taller tool bit holders I have. Just clamping them in gives no backrake. I don't want to grind a 16 deg. backrake into the top of my bit.
Are there holders for this situation?
Have you guys made holder adaptors? or holders?
what can I do?

whitis
11-28-2010, 06:43 PM
Angling the tools, like in an armstrong/williams holder and lantern toolpost, can increase the probability and severity of accidents. When a straight tool grabs, it deflects away from the work; in an angled holder, it deflects into the work and grabs harder. Next thing you know, the work is ripped out of the chuck and becomes a projectile or you are stripping teeth off your gears or ripping your toolpost off the compound.

Ocassionally, you may need the armstrong style tool holder to get into tight spaces. I would be tempted to use the carbide style holders, which hold the bit straight, in such cases and grind the rake on the tool.

Effectively, you are cutting above center even when the tool bit is adjusted on center. The horizontal line from the axis of rotation of the work isn't what is important; what is important is the line between the axis of rotation and where the tool bends. The radius of the workpiece vs the geometry of the tool and holder also factors in as small diameter work can give you some clearance when the tool bends.

This could also be a problem with diamond style HSS toolholders, though in some cases the bit will slide in the event it digs in rather than dig in further.

Arthur.Marks
11-28-2010, 07:26 PM
I don't want to grind a 16 deg. backrake into the top of my bit.
:confused: Why not :confused:

Paul Alciatore
11-28-2010, 07:46 PM
Here we go again with grinding tools.

Ovservation one: 16 degrees of back rake is a lot. Depending on what you are cutting, probably way too much. Back rake values in the range of +/- 10 degrees are probably the normal range. The greater the backrake, the more likely the tool will break or wear rapidly. The less the backrake, the stronger the tool edge is. Negative values are considered less and produce the strongest edges.

Observation two: until you are more experienced, I would suggest you start with rake angles in the range of 4 to 10 degrees for HHS tools. You can get some experience with your lathe and your materials and then start to modify the angle as needed.

Observation three: the main thing you need when cutting metal is rigidity. This is an advantage of a turret style holder. It is solid, sturdy. You really don't want to throw this advantage away by adding any extra devices or adapters between the turret holder and the tool. Simple is best.

Now, how to get the proper geometry with your tool holder. Many, but not necessairly all, turret tool holders will hold the tools in a horizontal position. This is not necessairly good or bad, but it is a neutral starting position for the angles so whatever angle you want, that is the angle you must grind. I suspect from your comment "Just clamping them in gives no backrake." that your holder is of this horizontal type. So, you MUST GRIND whatever angle you need to cut with into the tool: both rake and clearance. This means that you should grind the backrake angle on the top of the tool. And grind the clearance angle on the front and side edges as needed.

Another consideration is how you will bring the tip of the tool to the center line of the lathe. This is important because if it is above or below the center line, then the rake and clearance angles will change with the diamter of the work as you cut it. In order to actually use the angles you ground the tool to, you must be on the center line. If you are above it, the rake angle will be greater and the clearance angle will be less. This can become extreme and the clearance angle could become negative. A negative clearance angle would mean that the tool is rubbing on the OD a bit below the cutting edge and the cutting edge is not even in contact with the work. It can not cut under these circumstances. You must have clearance in order to cut. This is true for any cutting edge. On the other hand, if you are below the center line, then the tool may have a lower rake angle and cutting can be harder in a smaller machine. If taken to extremes, the tool can even be drawn under the rotating work with distasterous results. Oh, and if you are facing a part, you must be on the centerline to cut to the center of the part. Too high and you get a bit of a mess. Too low and you leave a button.

Your turret holder has been designed with a particular sized tool in mind. Most such holders do not incorporate any means for adjusting the height of the tool. So you must establish this height to put the cutting edge on the center line by several parameters. First, the tool size. If the tool is too small, it can not reach the centerline without shimming. If too large, it will have to be ground down (on the top side) to the proper height. So it is best to use the size that the holder was intended for. Before standarizing on the 3/8" size, be sure this is the intended size for your holder. Second, the tool must be ground properly. A larger tool can be ground down to the correct height. Third, you can use shims under the tool to bring it up if it is below the center line. A bunch of sheet metal shims in several thicknesses can be very useful. If you use shims, be sure they extend to the front edge of the holder or the tool will be unsupported for whatever amount it is short of it: another loss of rigidity.

Final observation: a turret holder is great for a production situation where several tools can be ground and mounted properly and then hundreds or thousands of identical parts can be made by just rotationg the turret. However, it is not very good in a small or home shop environment where parts tend to be made in singles or very small quantities. A far better tool holding system there is the quick change style holders. These allow a wide range of tools to be mounted and adjusted for the proper centerline height and then removed and remounted in the exact same position in seconds. You are not limited to the four or six tools that a turret will hold and tools can be removed for sharpening and returned to the same position (minus what was ground off) to continue the job with minimal adjustments. And if you must remove a tool from a turret holder, you instantly loose it's position. In a quick change holder, you can remount it and continue working on the same or an identical part with the same dial readings.

Abner
11-28-2010, 07:59 PM
whitis - Is it ok then to use a 3/8 HSS without backrake- I'm confused here. I understand your comment about digging in with an armstrong holder- I hadn't thought about that.

Tubal cain showed an @ 83 deg R hand cutter grind. 10 deg relief on the vertical faces and a 10 deg slope on the top. He mentioned the 16 deg tool holder angle (16 deg) multiple times. I assume this is for chip breaking?

Still confused.

AM - My concerns are the constant need to adjust the height after sharpening with shims and how far back would that 16 deg need to be? Is it for chip breaking or ? And that would make a compound angle on the top - 16 deg from the tip back and 10 deg from left to right at the same time? Am I being a wus?

Paul - Ah! Thanks I thought I understood what the issues were. The turret came with the lathe and carbide insert holders as well. My experience using carbide is with a table saw and wood. I was very unhappy with the finish results of carbide on cold rolled shaft steel, and I chipped a lot of inserts.
From your description I could use HSS whit the 10 deg relief(s) and a 10 deg slope on the top, once shimmed to center it could be resharpened and should be aligned to center when reinstalled. Increasing the backrake would help it 'peal' the metal?

Carld
11-28-2010, 09:09 PM
The only time you may use a 16 deg back rake is on aluminum and even then it is under certain conditions.

You don't need holders for HSS cutters in a turret tool post unless your using real small, say 1/4" sq., cutters.

As others said, 10 max is all you need and you can use "0" back rake for almost everything you do and be ok. Look in the Machinery Handbook for the tool shapes and start grinding.

I suggest you put the carbide insert holders away until you learn how to grind and use HSS cutters. I also suggest you make a BUNCH of different thickness shims that are the same size as the slot in the side of your turret tool holder, you WILL need them.

Get a bench good bench grinder and have a coarse and fine wheel on it and don't use it for anything but the lathe cutters.

Arthur.Marks
11-28-2010, 09:51 PM
No, no offense intended! :) Grinding rake, if any is to be used, is just how it's done. I'm not too great at the off-hand compound angles either. FWIW, when I grind HSS from blanks, I use this little handy device: http://alisam.com/page/1gu8x/Metalworking.html It comes with instructions---which I believe are a copy from "How to Run a Lathe" book put out from South Bend long ago. Any case, it gives a nice chart with example grinding angles (including back rake suggestions) for different applications which may help you out.

Carld
11-28-2010, 11:34 PM
:cool: I want to tell you a secret. The back rake toward the tool holder and the back rake away from the leading cutting edge is NOT CRITICAL. I know this will be hard to believe but it's true.

The average front and side clearance is about 5 deg, did you notice I said ABOUT.

The angles on the top of the cutter can be from about 5 deg negative to 5 deg positive. Notice the word ABOUT.

The angles can be more than 5 deg to suit the job it will do. Experiment with it.

Here is the rest of the secret, the angles will vary according to the material being cut and the rpm, feed and depth of cut.

There is nothing magic about lathe cutters. You grind one and if it don't work you regrind it until it works.

Slap the damn cutter on the grinder and grind it and try it. Eventually you will learn what works.

whitis
11-28-2010, 11:47 PM
whitis - Is it ok then to use a 3/8 HSS without backrake- I'm confused here. I understand your comment about digging in with an armstrong holder- I hadn't thought about that.





Generally, you will want some positive rake on HSS tools. Different angles are better for different materials. You will find some tables of angles to use for different materials, though the numbers vary a bit. Generally, the more positive the rake angle, the better it cuts but the more fragile the cutting edge. For harder materials, interrupted cuts, or more brittle cutting tools, decreasing the rake angle gives better tool life.
http://www.metalartspress.com/PDFs/Sharpening_Steel_Lathe_Tools.pdf
http://www.ic.polyu.edu.hk/student_net/training_materials/IC%20Workshop%20Materials%2009%20-%20Metal%20Cutting%20Processes%201%20%E2%80%93%20T urning.pdf
http://www.rulezman.com/rulezman_workshop_2/downloads_files/UnionGrinderManual.pdf

Threading may be done with 0 degrees rake; for small diameter work, the rake angle may actually affect the thread profile.


Tubal cain showed an @ 83 deg R hand cutter grind. 10 deg relief on the vertical faces and a 10 deg slope on the top. He mentioned the 16 deg tool holder angle (16 deg) multiple times. I assume this is for chip breaking?

No, the 16 degree tool holder angle gives the top (back) rake on a tool that has not had a top rake ground into it.


AM - My concerns are the constant need to adjust the height after sharpening with shims and how far back would that 16 deg need to be? Is it for chip breaking or ? And that would make a compound angle on the top - 16 deg from the tip back and 10 deg from left to right at the same time? Am I being a wus?
This is one of the reasons for the popularity of quick change tool holders that don't need shims.
Yes, the top face of a cutting tool will generally be a compound angle.


Paul - Ah! Thanks I thought I understood what the issues were. The turret came with the lathe and carbide insert holders as well. My experience using carbide is with a table saw and wood. I was very unhappy with the finish results of carbide on cold rolled shaft steel, and I chipped a lot of inserts.
From your description I could use HSS whit the 10 deg relief(s) and a 10 deg slope on the top, once shimmed to center it could be resharpened and should be aligned to center when reinstalled. Increasing the backrake would help it 'peal' the metal?

Lathe cutting tools don't peal the metal, they shear it. It is a little complicated. But the thickness of the chip is not the same as the thickness of the metal removed.

jugs
11-29-2010, 05:19 AM
Here we go again with grinding tools.

So much good info has been posted on here again & again on this & other subjects, that then gets lost in the info-mess, so constantly needs repeating.

How about creating a sticky thread on the Basics of tool grinding that we can direct pepole to.

john
:)

Abner
11-29-2010, 08:08 AM
Thank you all for taking the time to respond to my questions. I need to buy some HHS sq. cutting blanks and was having the hardest time with the backrake issue, and how to make that happen.

I agree there is a lot of really valuable information on this thread. From people with experience which makes all the difference imho.

My turret takes a 5/8" sq carbide holder. I was thinking 3/8' sq HHS M2 blanks to start with and shimming it.

Carld
11-29-2010, 09:15 AM
Abner, I used 3/8" HSS with shims for years until I got a QC tool post that height is adjusted with a nut on a screw. The shims work great just measure the tip of a very sharp dead center in the headstock to the bottom of the slot on your four way tool post. Measure it as accurately as you can because that is important.

Now you have the total height of the cutter and shims. You have to keep in mind that measurement is from the botttom of the stack of shims to the top of the cutting tip. Sometimes from grinding, the cutting tip is lower than the top of the square cutter. Then you measure from the bottom of the shims to the top of the cutter tip. Some even make a setting tool that looks somewhat like a square to set the shims and cutter on with a scribe line where the tip should be.

It's more important to keep the tip at or under the center line of the axis of the spindle or the cutter will only rub on the work and not cut anything without extreme pressure.

Everyone will have their own way of setting the cutter height after some experience with doing it.

noah katz
11-30-2010, 10:01 PM
Lathe cutting tools don't peal the metal, they shear it.

With no rake that's true but increasingly less so as back rake goes positive and becomes a slicing action.

Carld
11-30-2010, 11:29 PM
You will get a lot of different opinions on that but the removal of metal in a lathe is a shearing and chisel action as I see it. I can't really call it a slicing action. A peeling action may be a more acceptable term.

We seldom use a back rake of more than 10 deg and the only time I used a 15 deg back rake with a radius to it was when I was machining some aluminum castings that were of terrible quality aluminum. Actually the angle at the cutting tip was probably in the range of 45 deg because of the 1/8" radius that was a chip breaker.

Back to the subject, no, I can't agree that it's a slicing action.

whitis
12-01-2010, 01:35 AM
With no rake that's true but increasingly less so as back rake goes positive and becomes a slicing action.
Actually, if you read the metal cutting theory books and papers, positive rake cutting is shearing. For example, in the 1961 edition of Black's Theory of Metal Cutting, Figure 3-1 shows a 30 degree positive rake shearing and Fig 3-2 shows a 20 degree positive rake shearing. Figure 3-15 shows a micrograph of a 10 degree positive rake cut, which results in a 16 degree shear angle and a 0.004" depth of cut results in a 0.015" thick chip.

Boucher
12-01-2010, 08:35 AM
One of the advantages of the Turret type tool post is that it is much more ridgid than the Armstrong. That is a significant advantage!!! It does take a little work to assemble the appropiate shims but it is well worth doing. It really surprises me how many people have but don't use their Turret tool posts.

The rocker type mount makes it easy to experiment with back rake angles. It will quickly convince you that in most but not all instances it is not critical.

AllThumbz
12-01-2010, 10:01 AM
So much good info has been posted on here again & again on this & other subjects, that then gets lost in the info-mess, so constantly needs repeating.

How about creating a sticky thread on the Basics of tool grinding that we can direct pepole to.

john
:)

John,

Good idea...

I did just that on my site. There are links and PDF files of methodologies. You have to register first, which takes a minute:


http://hobby-machinist.com/index.php?topic=367.0

Feel free to share.

noah katz
12-01-2010, 02:38 PM
I was thinking that the reduction in cutting force (how much?) was due to the concentration in force and separating action that slicing gives, with the resulting attendant tensile stress.

But I guess with such shallow rake that's not such a good argument.

Carld
12-01-2010, 02:56 PM
noah, is that a serious question? Could you ask that in a different way?

noah katz
12-01-2010, 11:05 PM
Yes.

It's often noted that higher rake angles give lower cutting forces and are a benefit for smaller less rigid machines, and I was just wondering how much lower.

Maybe on a small machine deflection is enough in the middle of the bed to measure with a dial indicator.

jugs
12-02-2010, 05:54 AM
Yes.

It's often noted that higher rake angles give lower cutting forces and are a benefit for smaller less rigid machines, and I was just wondering how much lower.

Maybe on a small machine deflection is enough in the middle of the bed to measure with a dial indicator.

:eek: :eek: If that happens you have 2 options-

1, Take only light cuts & finish with a ba$$td file accuracy may be better.

2, The preferred option - scrap the machine & get a proper one

john
:)

Carld
12-02-2010, 09:49 AM
Back rake on the cutter toward the tool post is not necessarily what you want. To reduce the cutting load you use a positive rake on the opposite side of the direction of cut. With a HSS right hand turning cutter you will be turning a shaft toward the head stock so you want the positive angle perpendicular to the axis of the spindle with no back rake toward the tool post. I don't use back rake toward the tool post very often.

A left hand cutter is used mostly to face the end of a shaft and the back rake would be away from the axis of the lathe.

The lantern tool post cutter holders hold the HSS cutters at a positive angle in the holder and at times that is helpful but the problem is if the cutter hangs up in the cut it will push the cutter down and into the work. If you use the holders for carbide cutters they are held in a "0" back rake position in the holder. When a cutter in one of them hangs up in the work it is pushed down and away from the work and does little damage.

If your using a four way tool post or a QC tool post the cutters are clamped in with "0" back rake and will not be moved down in an accident but any back rake in any direction has to be ground into the cutter it's self.

I prefer to have any back rake on my cutters opposite the direction of the cut being made.

noah katz
12-02-2010, 06:15 PM
Back rake on the cutter toward the tool post is not necessarily what you want. To reduce the cutting load you use a positive rake on the opposite side of the direction of cut. With a HSS right hand turning cutter you will be turning a shaft toward the head stock so you want the positive angle perpendicular to the axis of the spindle with no back rake toward the tool post. I don't use back rake toward the tool post very often.

Yes!

This just occurred to me a couple of days ago, and is why I waffled and just said "rake" in my last post, and I've been meaning to bring it up.

Seems to me that this removes the need for a tangential or Wimberley tool holder:

The biggest appeal to me was not having to grind in back rake, as it's very tedious, wasteful of the bit material, and changes the cutting edge height.

Now it seems that's all that is required (for the most common turning toward headstock) is a horizontal toolbit with side & front clearance and side rake.

When the edge dulls you just grind the front face and you're done.

Am I missing something?

Carld
12-02-2010, 08:17 PM
You got it. once you get the tool the way you want it just grind either the top or the side. If there is heavy wear you may have to grind both surfaces.

The reason I don't like the tangential is because of the compound back rake and the way you have to grind the end of it. However, with the Wimberley you just grind the two side clearance angles because the cutter is held in at an angle to start with. I still prefer the surface leading into the cut to be "0" rake.

For that reason I still intend to make my own holder or buy a diamond insert holder to turn and face the shoulder in one operation.

How you sharpen your cutters can vary according to what you like. There is no iron clad rule, it just has to cut right and clean and make you happy. As time goes by you will find what works for you and since every job is different things may change all the time. After a while you will have a big drawer full of cutters with all kinds of angles ground on them. Once I get a tool ground the way I want for a particular cut I don't change it for another set of angles, I grind another tool. If your not careful you'll end up with a drawer full like mine.

http://i82.photobucket.com/albums/j276/yeathatshim/PC020006.jpg

The cutters on the right are new unground, the cutters in the center are ground for different jobs and the cutters on the right are shortened for using in boring bars. the same size drawer full of brazed cutters is set up a little neater but I didn't take a photo of them. The cutters in the can with the round ends are special grinds for aluminum and have compound back rakes with a radius ground in them that I mentioned before. Ain't worth a crap for anything but aluminum though.

noah katz
12-02-2010, 09:25 PM
You got it. once you get the tool the way you want it just grind either the top or the side.

Grinding the top/side is exactly what I want to avoid, because it makes the front of the bit smaller and smaller.

Why not the front?

Carld
12-03-2010, 12:20 AM
Take a 3/8" sq. right turning tool for example. To make the tool you grind a 5 deg relief on the left side of the end of it parallel to the side and then a 5 deg positive relief on the top from the left edge toward the right side parallel to the top. The tool bit will come with a about a 10 deg relief on the front end, well, the angle is on both ends actually so you don't have to grind there.

Now when you put the cutter in the tool holder and start turning toward the head stock you will see the wear on the left top edge where the metal is rubbing across the cutter and on the leading side where the cutter is rubbing against the work. Most the wear will show on the top of the cutter on the leading edge. If you have enough side relief ground on the left leading side there should be little or no wear there.

When the wear finally dulls the cutting edge you have to decide to take a little off the top surface to sharpen it or take a lot off the side to sharpen it. You would have to take the DOC off the front of the tool to get it sharp again. If you were taking .050" DOC the wear would be .050" along the top surface and to sharpen the cutter you would have to remove that .050" to get to a sharp area. That's to much grinding and to much waste and it's just the wrong way to sharpen.

When you sharpen the top and side you have to keep raising the cutter to keep it on the center line but you can get a sharp edge with very little grinding making the tool last longer. Sometimes you will have to grind a little off the front to get the tip sharp. Eventually you will have to grind the end off and start over. That's why you don't grind more than a 1/4" long flat on the side and top of the cutter and your not likely to take a 1/4" DOC anyway.

Grinding a cutter is simply thinking what you want it to look like and grinding it that way. Don't make the flats any longer than you need and you won't waste the tool steel. When you sharpen the cutter only take off enough to make it sharp, don't get carried away. Touch it to the wheel and look at it with a magnifying glass and touch it more if needed. Some times you can just dress it on a hand stone or diamond lap. I use a headband magnifier I can flip up and down as needed to inspect the cutting edge.

One of the hardest things to learn is how to lay the ground surface flat on the wheel when your resharpening the cutter. Some people can grind a nice looking flat because they have learned how to lay the steel on the wheel flat against the spinning wheel. Others show a surface with many flats on it and maybe a rounded leading cutting edge. You may have to waste a few pieces of tool steel to learn but you need to learn. In fact it's easy to learn using some 3/8" sq. keystock and it's cheaper than tool steel.

Learn how to grind cutters with keystock and when you get it right switch to a piece of tool steel. When I started I bought a set of preground HSS cutters and then tried to copy them on keystock. When I was confident about grinding I started using tool steel to grind on.

noah katz
12-03-2010, 12:42 PM
5 deg positive relief on the top from the left edge toward the right side parallel to the top.

= top rake, right?


If you were taking .050" DOC the wear would be .050" along the top surface and to sharpen the cutter you would have to remove that .050" to get to a sharp area. That's to much grinding and to much waste and it's just the wrong way to sharpen.

Gotcha.

For grinding I'll make some jig blocks with the angles built in to use on the tool rest.

Is the concavity you get on a bench grinder an issue?

I was thinking of getting one of the affordable import carbide grinders.

Thanks for all the instruction, Carl.

J. Randall
12-04-2010, 02:06 AM
= top rake, right?



Gotcha.

For grinding I'll make some jig blocks with the angles built in to use on the tool rest.

Is the concavity you get on a bench grinder an issue?

I was thinking of getting one of the affordable import carbide grinders.

Thanks for all the instruction, Carl.

Noah, to me rake and relief are the two most abused terms in machining, when people on the web get to trying to explain them.
The way I look at it, anything on the top is rake, that could be neutral, back, side. It can also be a combination making it a compound rake. The other angles on the front and sides of the tools are relief angles. When I was trying to get my head around grinding my own tools, I read a lot of posts from people who knew what they were doing, but using the wrong terms.
James

Abner
12-04-2010, 08:52 AM
Carl- Thanks for the descriptions starting from blanks. I ground a 3/8" HHS cutter yesterday to make a replacement pully for a new come-along. Those stamped steel pulleys they use in the dbl line hook assembly with are not worth a damn.
I can see where using my lighted magnifier/ and a stone is needed.

NK - I have one of those HF tool grinders. So far I would conditionally recommend it. The ability to grind on the side of the wheel with a platform that will support the work is really nice. Same goes for the sliding fence. Do not expect accuracy with the angle scales. I take it from what others have posted that there is no penalty for being 9-11 degrees when trying for 10.

J Tiers
12-04-2010, 09:53 AM
Most of what CarlD says I totally agree with.

I ALMOST NEVER use any back rake towards the holder.

Think about the cutting forces, and the cut.

The cut occurs, if you are moving towards the H/S, as usual, on the LEFT SIDE of the cutter. You can maybe also imagine the cut as occurring on the top of the tip, as if you were unwinding the chip like a string, but I don't think that is a worthwhile "model" of what is happening. In practice, if you look at the chip, it will be coming off the left side of a rounded cutter nose, etc.

On lathes we are likely to have, the DOC and feed is not such that the "unwinding model" is useful. If you have high HP, you can take a cut that WILL be more like that.

Then there is workpiece deflection. The more the cut occurs on the nose of the tool, the more force is trying to bend the work away from the cutter. that isn't helpful.

Unless there is a good reason why not (threading, cutoff, form tools, etc) I prefer to have rake sloping down from left to right, with the cut occurring on the left side of the cutter. That way forces are pushing the work into the chuck, and not deflecting it much. You can['t avoid every bit of crossways force, but you can get rid of most.

That rake does a couple things. yes, it makes a 'sharper" tool, of course. But it also let the chips flow away from the work without "piling up", so reducing force required. And it does tend to change the action from "plowing" to 'cutting", which leaves a better surface, as well as reducing forces.

I'd totally bag that old back rake thing except for special cases. Rake does reduce force, which is good on lightweight low power machines, so just change which way it goes, and you should be happier.

Oh. LOSE that lantern post..... they were fine in 1890..........

Carld
12-04-2010, 11:42 AM
The term rake is used for the top of the cutter and is meant to designate back rake and side rake. Everyone should understand back rake but side rake can be confused with side clearance. Side clearance is on the left or right side of the cutter and rake is always on the top. Side rake can be sloping to the left or right and is perpendicular to the side of the cutter. If you add back rake to side rake you have a compound angle. As I said before I seldom use back rake and side rake together. I prefer to use side rake on a cutter.

The problem is, which way does the rake go? If the cutter is a right hand tool the cutting edge is on the left and the top relief/rake starts at the cutting edge and angles down or up from there to the right. That is positive side rake. Then we have back rake and that goes from the tip toward the tool post which is positive rake. Now, under some conditions you may want negative front rake or negative side rake or maybe both.

At all times you keep the very tip of the cutter at the axis center line of the lathe spindle for best results.

You don't want to get me started on the terms left and right hand turning tools. I would love to use a 3 foot long 1" stiff rubber hose on who ever thought that misleading term up. Anyone with common sense would say a left hand turning tool cuts to the left but noooooooo, some ignoramus long ago decided it was a right hand turning tool. I believe his intent was to confuse novices and make the trade seem harder to understand and he certainly didn't use the KISS method (Keep It Simple Stupid). However, everyone has decided to follow along with that duffus and continue to use those terms.

Back to the lathe cutters, if your looking up lathe cutters look for SINGLE POINT CUTTERS in the index of any reference manual. I looked in my Machinery Handbooks and they don't address single point lathe cutters even as far back as my 1924 Machinery Handbook. My 1940 American Machinists Handbook does cover single point cutters for the lathe and planner. It doesn't hurt to have a cabinet full of old books.

I doubt you will find any description in handbooks after 1940 as that seems to be the cut off area. The best books describing lathe cutter shape is How To Run A Lathe by South Bend Lathe Works and Manual of Lathe Operation and Machinists Tables by Atlas Press Company. Everyone should own one or both of them and there are reprints available and maybe even downloads.

EDIT: Lantern tool posts are a thing of the past but I am quite fond of them from using them for many years. The best advantage of them is their versatility of angles and getting in close places. The downside is their tendency to cause lots of damage if the cutter hangs up and that can get real dangerous. Yes, go for the QC tool post, I have.

noah katz
12-04-2010, 03:25 PM
The way I look at it, anything on the top is rake, that could be neutral, back, side. It can also be a combination making it a compound rake. The other angles on the front and sides of the tools are relief angles.

That's my understanding and I think that's the way I've been using the terms.

I guess another way of saying it is that the raked surface will have the chip flowing over it, and relief is for clearance.

whitis
12-04-2010, 04:17 PM
You don't want to get me started on the terms left and right hand turning tools. I would love to use a 3 foot long 1" stiff rubber hose on who ever thought that misleading term up. Anyone with common sense would say a left hand turning tool cuts to the left but noooooooo, some ignoramus long ago decided it was a right hand turning tool.

That is a matter of perspective. It is a "right handed cutting tool", not a "right edge cutting tool" or a "right cutting tool". Although, as it turns out, a "right-cut" tool has been defined (Machinist's Dictionary) as one which cuts on the right when viewed from the front of the tool (as seen by the work or the person inspecting the tool with the front facing them) and is more or less the same meaning as a right handed tool, so even focusing on the tool and the edge doesn't necessarily lead to reversing the convention. A right handed tool removes the right side of the work and a left handed tool removes the left side of the work. Right hand cutters cut on the right side of the work piece and left hand cutters cut on the left (think a shoulder). And the engine lathe evolved from machines where one actually used gravers or gouges held in the hand. A non-ambidextrous craftsman may not actually switch hands when using the tools but the cutter then was conceptually more an extension of our hands. If you were to reach out and grab the work by the shoulders (whether intended shoulders or the temporary shoulders that form while we are turning to diameter), the right hand tool goes where your right hand would be and the left hand tool goes where your left hand would be. If our hands were capable of cutting metal, we would use our right hand where we use a right handed cutting tool. Our hands even, naturally at rest, have an somewhat appropriate rake angle. If we are teaching students or apprentices and using our hands to illustrate the cuts, our right hand goes where the right handed tool does. Also, the turner normally works on the right hand side of the work, given that you have a bulky spindle and possibly chuck on the left and the typical user was right handed and thus lathes were made for right handed people. A right hand tool is the "normal" "right" tool and a left handed tool is its evil twin. This was "normal" and turning on the other side was ass-backwards in the same sense that a right handed thread is arbitrarily considered normal and a left handed thread is considered an ass-backwards one. We even insert a transposing gear to change a right handed lead screw to be effectively left handed when turning with a left handed cutting tool (or vice versa). The word "sinister" actually derives from an ancient prejudice against left handed people. Our right hand has, for most of the population, more dexterity and our left hand is more awkward, just as cutting on the left hand side of the work on a right handed lathe is more awkward. A left handed cutting tool would be the normal cutting tool on a left handed lathe; and occasionally a southpaw will post on metal or woodworking forums asking if anyone makes left handed lathes.

In a right handed tool, when viewed from the operator position on a lathe, the work being cut is on the left and the tool is on the right and the chip is usually sheared to the right and comes off on the right side. The tool is not only on the right hand side of the work, it is on the right hand side of the cutting edge.

There are always two ways to look at these types of movements in two or three dimensional space where there is an object and and observer. When you are reading a document, do up and down move the window over the document or do they move the document in the window? When you have a CAD model on the screen, do the controls move the object being viewed or do they move the viewport. When you turn the steering wheel on a car, do you move the car relative to the road or the road relative to the car. If I have an object on a motorized platform, I use the controls one way to move the object relative to me, but when I hop up on the platform and want to move an object relative to me, I reverse the controls. When you turn the controls on a machine tool, do they move the work or do they move the cutter. On many machines it is even a combination of both, for mechanical reasons. We often think of moving the cutter, rather than the work, even though it may be the work that is actually moving. There are always the two different ways of resolving relativity and the conventions we use in different situations are arbitrary. A century ago, Einstein spelled out that all motion is relative and there is no absolute frame of reference. We have arbitrary prejudices towards certain frames of reference, that flip flop around as we do different things. We flip flop around between using the earth and our own bodies as a frame of reference, for example. Right and left also change when we flip the tool around. In archery, a right handed bow is one we operate with our right hand, not one we hold with our right hand. For scissors, right handed scissors are the ones we hold in our right hand. When we are facing someone, their right hand is on our left. Stage right is the actors' right, not the audiences.

There are several implicit assumptions likely to be made by by those who have trouble with the handedness of lathe tools:
- That the tool, and not the work, is the frame of reference
- That it refers to the side cutting edge portion of the tool
- that the viewing perspective is from the operator position on a lathe in the usual configuration with the cutting tool on the operator side of the cross slide.

We use right handed threading tools to cut both left and right threads, depending on the setup, and likewise for left handed tools. It depends on whether the threads are inside or outside, the tool is on the front or back side of the axis of rotation, and the spindle is turning forward or backwards.
A chart was posted in a recent thread showing the combinations.
http://img.directindustry.com/pdf/repository_di/16116/vardex-thread-milling-thread-turning-main-catalog-english-inch-050ea-95733_122b.jpg

It turns out that right hand turning tools are consistent with right handed drills or end mills. If you substitute a right handed end mill or boring bar for a right handed turning tool, it will work, more or less. Even though a right handed end mill is named for turning in a "right hand" direction like a right hand drill bit or tap. Likewise, a right handed internal threading tool will sorta work if moved into the position of a normal right handed turning or facing tool.

In some fields, such as electromagnetics, screw handedness, or coordinate spaces, right or left handed has to do with the way the fingers curl or the orientation of the thumb and first two fingers held in a mutually orthogonal position.

The exact origins of the naming of right and left handed cutting tools seem to have been lost in antiquity. It may have originated in a time when wood was being cut instead of metal, when tools were held by hand, when metal cutting tools were bent in a forge rather than using straight tool blanks, when files were used instead of normal cutting tools, etc. The terminology may have been coined when the tooling was invented or considerably later.
It made sense at the time and it makes sense now, though not necessarily for the same reasons.

Carld
12-04-2010, 06:17 PM
Yes, I have read all that crap before so I'll ask you this.

Do you stand on the back side of your lathe and look at the cutter to see what to call it?

I don't.

Do you point the cutting end of the lathe tool toward you to see which direction it cut or what to call it?

I don't.

Does everyone pick up a lathe tool, hold it in their hand with the cutting end away from them and think, what is this, a left or right?

I do.

That is the common sense part of it. I'll tell you an experiment, hand a student machinist a right hand cutting tool and ask him/her which way it will cut and they will say to the left. Then ask them what the cutter would be called and most if not all would say a left hand cutter, NOT a right hand cutter.

Don't believe it, try it, I have tried it time and time again and it always comes out the way I just described.

This is one of few machining terms that I totally disagree with as a matter of common sense. It always confuses students your trying to teach machine work. It is the stupidest term in the machinist trade.

The problem is, it's been used so long common sense can never prevail over stupidity.

Yeah, I just look at the tool and know it is opposite of what it looks like but it still pisses me off when I think about how dumb it is.

Abner
12-05-2010, 10:11 AM
Right and left cutters must have been named about the same time as 'current' flow in electrical circuits.

'electrons' flow in the opposite direction as 'current'.