# Angle of HSS turning tool to work



## Jmanb13 (May 3, 2017)

As I've been reading more and more about grinding HSS turning tools.

One of the most complete ones i've seen is the following.
http://www.steves-workshop.co.uk/tips/toolgrinding/toolgrinding.htm

Specifically this picture.






I see information around all the different relief and rake angles for different materials, but not the side cut or end cut angles.

Does the side and end cut angle matter and is there a recommended angle? 

In regards to all of these angles, do these angles all assume the unground portion of the tool is 90 degrees to the work?


----------



## Ulma Doctor (May 4, 2017)

side and end angles can be anywhere from 5* to 15* in most cases
the back rake shown in the drawing is for when using lantern type toolpost with a toolholder
a lot of the armstrong type holders have a 7* angle built into the holder, you'll need a bit more end relief in that case
a QCTP won't need the back rake and can be more acute on the end relief.
side relief, do as you please anywhere 5* to 20*.
5* for tough materials, up to 20* for easier to turn materials


----------



## mikey (May 4, 2017)

The side cut and end cut angles in the illustration are more commonly referred to as the side cutting edge angle and end cutting edge angles, just to clarify the terminology in case you need to look it up. 

Technically, they do matter. In the tool illustrated above, that is the profile for a roughing tool intended to be used with the shank perpendicular to the work. Note that the end cutting edge angle is less than 90 degrees relative to the side edge and this allows the nose of the tool to access corners so you can use that tool shape to both rough and face. Of course, you will need to alter the tool angle to face with it but the same tool will both turn and face because of that more acute angle.

The side and end cutting edge angles will vary with the purpose of the tool. Roughing tools will have a less acute side cutting edge angle and facing and finishing tools will have a more acute side cutting edge angle. Traditionally shaped tools, as shown below, were used with the shank perpendicular to the work and these different angles were intended to allow the tool to work better for different operations.






When the tool is positioned with the shank perpendicular to the work, the side cutting edge angle is equal to the Lead Angle (LA) and the LA has an impact on cutting forces and finishes. The less acute the LA, the lower the cutting forces are so a roughing tool has a less acute side cutting edge angle. Conversely, a more acute LA will produce a better finish so the finishing tools have a more acute side cutting edge angle.

Of course, most of us use a QCTP nowadays so these shape constraints are not as rigid as they used to be because we can turn the tool to any angle we want. In this case, all we need to assure is that the end cutting edge angle is less than 90 degrees so we can cut shoulders. 

Insofar as the relief and rake angles are concerned, that is a much deeper discussion but yes, they do matter ... a lot.


----------



## Jmanb13 (May 4, 2017)

I do have a QCTP and that is what really prompted me to ask the question, because I can have the HSS tool approach the work at any angle I want.

I have the southbend how to run a lathe book which lists the tool shapes you mentioned in your post but of course they had a lantern tool post in mind. Do you know of any sites/books/videos that discuss grinding bit shapes specifically for use in a QCTP?


----------



## Doubleeboy (May 4, 2017)

Jmanb13,   Mikey is the guy when it comes to sharpening HSS, he has a long thread on it here on HM.  Might look up his past posts or do a search.  Very nice tutorial.


----------



## mikey (May 4, 2017)

To be honest, I haven't seen a really good book on this subject but there are tons of videos on YouTube. Most of the videos discuss tools suitable for use in a QCTP. The thing that sets a more modern design apart from tools intended for a lantern tool post are the back rake angles - they are either smaller or non-existent in tools made for a lantern tool post because the tool post holds the bit at an upward angle already so you don't need to grind  the angle into the tool.

Here is a thread I posted on grinding these tools. At the end of the original post are some links that may provide more info you might find useful. http://www.hobby-machinist.com/threads/how-to-grind-a-hss-turning-tool.52581/

When you use a HSS tool in a QCTP, the angle of the tool can be whatever you want. The questions I think you have are "what angle should you use, when should you use it and why?" I suspect every one of us has asked ourselves these questions at some point so you're not alone. The answers aren't that complicated so I'll try to explain them.

If you use an inserted tip carbide tool then the tool shank is intended to be held perpendicular to the work. All the clearance angles are designed into the tip geometry of the tool and insert and all you need to do is set the tip of the tool to center height, get it perpendicular and you're set. Brazed carbide tools are, in general, used the same way. HSS tools are shaped and have varying geometries so we need to understand things a bit better to get the best use out of the tool. 

A HSS turning tool cuts most efficiently when the lead angle of the tool is appropriate for the operation; to really understand this tool angle thing, you have to understand what lead angle is and what it does. 






The lead angle (LA) of a turning tool is determined by the side cutting edge angle of the tool and the way the tool is angled to the work. When the tool shank is perpendicular to the work then the LA is defined by the side cutting edge angle, as in the third example above. We can change this LA by turning our QCTP. So, what is the big deal about LA and why does it matter?

Basically, the LA of the tool alters cutting forces and affects finishes. The lower the LA, the lower the cutting forces are and the rougher the finish is; the greater the LA, the higher the cutting forces are and the better the finish is. This cutting force thing has a lot to do with the amount of surface area that is in contact with the work. When the LA is high, more of the side cutting edge is in contact with the work; when the LA is lower, less cutting edge is in contact. If you use a high LA and then try to take a heavy cut, cutting forces increase and you get chatter; backing off on the depth of cut reduces cutting loads, the chatter goes away and your finish improves. Conversely, using a lower LA brings less surface area into contact so you can take deeper cuts without chattering, albeit with a less refined finish. So, what does this have to do with tool angles and tool shapes?

The angle of the tool in use is determined by the operation. If you are roughing, angle the tool so that the LA is lower (like the middle pic above). If you are finishing, increase the LA (like the pic on the right, above). When the LA is low, you can take a heavier cut; when the LA is high, you have to take a lighter cut. The lower LA is used for roughing and the higher LA is used for finishing. For facing, the LA is negative such that you are cutting with the forward part of the side cutting edge, up near the tip. Facing depths of cut can be light or heavy, depending on your needs, because only a small area is in contact and the potential for chatter is lower.

Tool shapes are not as critical when we use a QCTP but they do have an influence on how much or little you angle your tool. You will find that the LA you end up using for a given operation will put the side cutting edge at an angle very close to what the older shapes did when their shanks were perpendicular to the work. 

Bear in mind that we're just talking about tool shapes and lead angles here. Cutting forces are definitely influenced by these things but the relief and rake angles have a much greater impact. That is a discussion for another time.


----------



## Jmanb13 (May 4, 2017)

Some great info there! So it seems with a QCTP you could conceivably grind a single tool and simply alter the lead angle do roughing and finishing cuts on the same tool.

I might need to try regrinding some of my bits to see what I can do. The existing ones I have been using were old used bits from ebay that I simply touched up and honed. They have worked well enough, but my surface finish leaves much to be desired.


----------



## mikey (May 4, 2017)

Yes, a general purpose tool shape will work for most tasks - just change the lead angle. However, do not make the mistake of thinking that shape is all there is. Each material you work with has required relief and rake angles and these are far more important than just the shape of the tool. 

What kind of lathe are you using? This also has an impact on how the tool is ground. Smaller, less rigid lathes will require larger rake and relief angles to lower cutting forces; larger lathes can get away with more standard angles. You will hear that tool angles are not important and close enough is good enough. The smaller the lathe, the less true this statement is.


----------



## Jmanb13 (May 4, 2017)

mikey said:


> Yes, a general purpose tool shape will work for most tasks - just change the lead angle. However, do not make the mistake of thinking that shape is all there is. Each material you work with has required relief and rake angles and these are far more important than just the shape of the tool.
> 
> What kind of lathe are you using? This also has an impact on how the tool is ground. Smaller, less rigid lathes will require larger rake and relief angles to lower cutting forces; larger lathes can get away with more standard angles. You will hear that tool angles are not important and close enough is good enough. The smaller the lathe, the less true this statement is.



1946 15" Leblond Regal Trainer. 500RPM in top gear, a little more if I overdrive the motor with my VFD.


----------



## Rockytime (May 4, 2017)

From a watchmaker's lathe, to a Sherline, to a 7" MaxiMat to a 12" lathe, I have always left the top of the cutter un-ground.  Perhaps I suffer from some inefficiency, I don't know. I guess it is because the things I cut brass, aluminum, 12L14 and some cast iron. These materials are so easy to turn I have to problem. Perhaps with more difficult steels I would have a problem. Another reason is it is one less face to grind. Another reason to use inserts, even on my Sherline.


----------



## mikey (May 4, 2017)

Okay, big lathe, low speed. You can grind a general tool shape and use the rake and relief angles found in any lathe tool angle table.


----------



## tomh (May 4, 2017)

The youtube channel "thatlazymachinist"   has some in depth videos on grinding the angles on HSS with some interesting results that are worth watching as well as "mrpete222".


----------



## mikey (May 4, 2017)

Rockytime said:


> From a watchmaker's lathe, to a Sherline, to a 7" MaxiMat to a 12" lathe, I have always left the top of the cutter un-ground.  Perhaps I suffer from some inefficiency, I don't know. I guess it is because the things I cut brass, aluminum, 12L14 and some cast iron. These materials are so easy to turn I have to problem. Perhaps with more difficult steels I would have a problem. Another reason is it is one less face to grind. Another reason to use inserts, even on my Sherline.



What is the maximum depth of cut you can take on your Sherline with those inserted tip tools or with a flat topped HSS tool in say, 12L14?

I ask because I also own a Sherline lathe and I can easily take a 0.050" deep cut in 12L14 with a good HSS tool. On my 11" lathe, I can easily take a 0.20" deep cut before I have to step the gearing down; and then I can go deeper. Tool angles enable a lathe to work much more efficiently than most of us realize.

Edit: @Rockytime , I re-read my post and it sounds like I'm being confrontational. My apologies as that was not my intent. What I really meant was that when we use side and back rake to full advantage it greatly reduces cutting forces and cutting temperatures so as to make a smaller lathe more efficient. I am not challenging your preference not to use them but I am suggesting that perhaps it might improve your experience. Again, my apologies - I sounded like a real dick and I didn't mean to come off like that.


----------



## wawoodman (May 4, 2017)

I've watched most of them, and I think I like This Old Tony.


----------



## jlsmithseven (May 5, 2017)

wawoodman said:


> I've watched most of them, and I think I like This Old Tony.



That's a pretty informative video. Great for beginners!


----------



## ddickey (May 5, 2017)

So this is why a solid tool post won't work if you use HSS ground tool bits.?


----------



## mikey (May 5, 2017)

If you only use inserted carbide tooling then the tool post can be fixed. If you plan to grind HSS tools with their profiles fixed, meaning you will grind a tool for roughing, facing and finishing for each material class then sure, you can fix the tool post. However, if you plan to use general purpose tools then you need the ability to alter their lead angles for different operations and that means the tool post cannot be fixed.


----------



## ddickey (May 5, 2017)

boo.


----------



## mikey (May 5, 2017)

Yeah, I know.


----------



## Rockytime (May 6, 2017)

mikey said:


> What is the maximum depth of cut you can take on your Sherline with those inserted tip tools or with a flat topped HSS tool in say, 12L14?
> 
> I ask because I also own a Sherline lathe and I can easily take a 0.050" deep cut in 12L14 with a good HSS tool. On my 11" lathe, I can easily take a 0.20" deep cut before I have to step the gearing down; and then I can go deeper. Tool angles enable a lathe to work much more efficiently than most of us realize.
> 
> Edit: @Rockytime , I re-read my post and it sounds like I'm being confrontational. My apologies as that was not my intent. What I really meant was that when we use side and back rake to full advantage it greatly reduces cutting forces and cutting temperatures so as to make a smaller lathe more efficient. I am not challenging your preference not to use them but I am suggesting that perhaps it might improve your experience. Again, my apologies - I sounded like a real dick and I didn't mean to come off like that.




Hi Mikey, Absolutely no offense taken. I do understand that proper grinds are necessary when doing production work. Time saved is more profit in the work. I, however, do mostly small projects such as making clock repair parts. Most often I am cutting brass and aluminum and occasionally 12L14, the 12L14 usually used for making small screw. At present I am building the PM Research small mill engine with aluminum castings with only a 1/2" bore. Very small engine. That is why I don't bother grinding the top relief.


----------



## hlj3 (May 7, 2017)

I really like this tool bit video. Good technique.






H L


----------



## benmychree (Jul 21, 2017)

mikey said:


> To be honest, I haven't seen a really good book on this subject but there are tons of videos on YouTube. Most of the videos discuss tools suitable for use in a QCTP. The thing that sets a more modern design apart from tools intended for a lantern tool post are the back rake angles - they are either smaller or non-existent in tools made for a lantern tool post because the tool post holds the bit at an upward angle already so you don't need to grind  the angle into the tool.
> 
> Here is a thread I posted on grinding these tools. At the end of the original post are some links that may provide more info you might find useful. http://www.hobby-machinist.com/threads/how-to-grind-a-hss-turning-tool.52581/
> 
> ...


The main thing about lead angle is that if you are roughing with zero lead angle, the tool tends to creep in, and likely cut undersize if you are roughing close to size; the lead angle puts pressure outwards on the tool, so that the tendency to creep in is eliminated.


----------



## Ken from ontario (Jul 22, 2017)

I have a question about back rake angle, what is a back rake angle?
 why it 's not needed with a QCTP?
if it is not often ground in a turning tool then why do we even mention it?

Please remember I have seen pictures of back rake angle (when I googled it), it sounds like it is used  for woodturning   when a sharper angle is needed  but the point of the question is, nowadays most people who grind their HSS cutting tools for turning and facing,do not incorporate a back rake angle in their cut but it's always mentioned .


----------



## Jimsehr (Jul 22, 2017)

Remember the quality of HSS tools is much better then it was when most of the old machining books were printed. I have been machining for over 60 years and can remember some of the poor tools of the day. In those days some of the angles made more sense then then they do today. I have even used dowel pins to make cutting tools in a pinch for cutting alum and other soft materials. Most tools today use top rake but they call it chip relief. I hand grind all my tools in my home shop even the radius tools used to cut the balls in my Avatar. I don't think many machinist of today 
grind tools old school. There is nothing wrong with that but in the old days you could not buy ready made tools like you can today. 
Jimsehr


----------



## GoceKU (Jul 22, 2017)

"In those days some of the angles made more sense then then they do today", This is funny, recently i've bought lot of HSS tools and first thing i thought those angles make no sense, how ever ground them was more concern about the chip braker then the cutting angle.


----------



## Jimsehr (Jul 22, 2017)

I started machining over 60 years ago and I thought some of the books on grinding tools were out dated then. And if I took as much time grinding a tool as the guy in the video did I would have been fired in no time. I worked in a production shop where time is money. Also guys in home shops are not making 1000 pcs at a time so if the cutting edge won't last for a lone time it is no big deal. If the tool works for what the home shop needs cut it is fine. I have tried some of the new cheap Chinese insert sets and they work great.
Jimsehr


----------



## GoceKU (Jul 22, 2017)

Jimsehr said:


> I started machining over 60 years ago and I thought some of the books on grinding tools were out dated then. And if I took as much time grinding a tool as the guy in the video did I would have been fired in no time. I worked in a production shop where time is money. Also guys in home shops are not making 1000 pcs at a time so if the cutting edge won't last for a lone time it is no big deal. If the tool works for what the home shop needs cut it is fine. I have tried some of the new cheap Chinese insert sets and they work great.
> Jimsehr



Cheap Chinese carbide insert work great for a short time, they seem to chip, break easy, the high quality german, dark grey, are my favorite, cut great and take lots of abuse and don't chip just cut and cut.


----------



## benmychree (Jul 22, 2017)

Back rake makes HSS tools cut more freely, rolling the chip back away from the tip of the tool; the Armstrong and similar too holders hold the tool on a 15 deg. back rake, but that much is not necessary; I think that the idea was that in sharpening the top of the tool that eventually it ends up more nearly parallel with the tool holder, as more is ground off the nose of the tool.  It gets to a point where you sharpen the cutting flank, the front and top of the tool, you keep up the same routine, and the tool can remain the same shape without cutting down its thickness behind the top rake grind, reducing its strength or making it necessary to cut the end off and start over with a whole new grind as you would with a quick change (parallel) tool holder.  Bottom line, you get longer tool life with the 15 deg. holders.
I do not agree that we had inferior HSS tools 50 years ago; the same premium brands and types are still here and available, although some shops may not have used them back then, as obviously they are more expensive.


----------



## Ken from ontario (Jul 22, 2017)

So it sounds like it is a personal preference to grind a back rake in the tool  and  not necessary .


----------



## benmychree (Jul 22, 2017)

Personally, I grind HSS tools for the lathe for use in QC tool holders with no back rake, just side rake, and avoid sharpening on top as much as possible.  I do not much use HSS tools for most work, but instead use triangular insert positive rake tools for most work except for the roughest and interrupted cuts, for which I use negative holders and inserts until things are pretty much rounded up, then switch to positive rake; this is for my 19" Regal LeBlond; for my 9" Monarch, I use HSS tools in a QC tool holder, ground as above.
I was "raised" in school shop with Armstrong type holders and learned to grind them mostly using the full 15 deg. back rake, only with ground in chip breakers, ground on the corner of the wheel; these curled the chips and made them less dangerous to the operator than a simple top rake which had to have sufficient and appropriate feed to accomplish the same effect, they were simpler for the learner to control chips, but are easier to damage with their more acute cutting edge.    When I got the old Monarch I thought I'd just use to tool holders that came with it; I'd forgotten what a pain they are to use!  I quickly bought a small starter set of QC holders.
What I think I meant was that tools with back rake cut more freely, but with QC tool holders that hold them parallel, you have to cut way into the tool bit back from the cutting point and with further sharpening, the bit is nearly ground half way through its height, weakening it, and ultimately making necessary cutting to tool off and starting the grind all over again.


----------



## mikey (Jul 22, 2017)

Ken from ontario said:


> I have a question about back rake angle, what is a back rake angle?
> why it 's not needed with a QCTP?
> if it is not often ground in a turning tool then why do we even mention it?
> 
> ... nowadays most people who grind their HSS cutting tools for turning and facing,do not incorporate a back rake angle in their cut but it's always mentioned .



Ken, I'll try to explain back rake but you must keep in mind that while it is, in fact, an angle on a turning tool it is one of two angles that determine a plane. This plane is actually a combination of the side rake and back rake angles and together they form the top horizontal surface of a turning tool. This plane can be angled in a positive, negative or zero direction, depending on how these two rake angles are ground. Here you can see the back rake angle from the side; it is that angle under the bit sitting on top of the ground tool:




Note that it slopes from the tip of the tool so that the back of the angle is lower than the tip; this is called positive back rake. Keep in mind that the entire top horizontal surface (the top plane) of the tool is also sloping back in a positive direction. Side rake is the other component of this top plane and it is sloping away from the tip as well so it is also positive.




So, as you can see, the top surface or plane of the tool is actually a flat plane, the angle of which is determined by the side and back rake angles.

Both rake angles can be positive, negative or zero. Just look at the tool from the tip. If the angles slopes away from the tip then the rake is positive. If it slopes toward the tip then its negative. If there is no slope to either rake angle then it is a zero-rake tool and is simply flat on top.

I know your question pertains to back rake but no tool angle works in isolation and the rake angles are no exception. The rake angles are the most important angles on a turning tool because they have a tremendous impact on cutting forces and cutting temperatures. In fact, they are the key set of angles that change when a tool is ground for different materials. If you look at a turning tool angle table, you will see that the relief angles change a little for each material class but the rake angles are the main variables that allow the tool to work with different materials. As the tool cuts, it separates the chip along a plane called a shear plane and each material we turn has an optimal shear plane angle that clears the chip from the cut. This is why the rake angles change for each material. I will stop with the shear plane garbage now but just know that back rake shortens the shear plane and thereby reduces cutting forces significantly. You can grind a tool without back rake but your tool will cut with higher cutting forces than it should/could.

So, what does back rake actually do (aside from its impact on the chip)? Basically, it alters the direction and speed of chip flow and also determines where the cutting forces are directed. 

Chip flow is largely determined by side rake. In general, cutting forces will run perpendicular to the side cutting edge. When you add in back rake, it changes the direction of the chip flow and the more back rake you have, the faster the chips exit the cut and this reduces cutting temperatures. 

If your tool has no back rake, all the cutting forces are focused on the side cutting edge. If you add back rake, you shift the cutting forces toward the tip of the tool and the more back rake you have, the more tip-ward the shift will be. This is why finishing tools, which cut with the nose radius, generally have larger back rake angles. On the other hand, roughing tools that cut mainly with the side cutting edge will have lower degrees of back rake. Facing tools cut mainly with the side cutting edge but up near the tip so these tools generally have more back rake than roughing tools but less than finishing tools. If you wish to see a video of how back rake shifts cutting forces, look up a video on tangential tools. 
Tangential tools have what amounts to significant back rake and as it cuts you will see the chip curling off the very tip of the tool. As the depth of cut increases you can see that it peels off a chip at the very tip. 
In general, back rake is an important angle. It plays a significant role in reducing both cutting forces (by shortening the shear plane) and cutting temperatures (by boosting chip flow out of the cut) and allows you to focus the cutting forces on your tool so it does what you need it to do. If you need more strength at the side cutting edge, reduce back rake. If you need better finishing potential, increase back rake. If you are cutting materials that work harden easily then getting the chips out of the cut faster helps to reduce temperatures at the point of cut; increasing side and back rake will help do that. 

Between the two rake angles, side rake is more important than back rake. Side rake greatly impacts on cutting forces because increases in side rake narrow the included angle at the cutting edge, thereby allowing for better penetration into the material. Back rake adds to this effect by narrowing the included angle at the end cutting edge and this also improves penetration (on top of the other things back rake does).

There are as many ways to grind a tool as there are tool grinders. Some of us think back rake is not important; some, like me, think it is very important and I use it to help me make the tool do what I want it to do. Other than my threading tools and brass tools, all my turning tools have side and back rake angles ground into them and I tailor the amounts of each rake angle to suit the material I'm working with. Its okay not to grind back rake into your tool but it will cut better for you if you do. 

Hope this helps, Ken.


----------



## Ken from ontario (Jul 22, 2017)

benmychree said:


> I was "raised" in school shop with Armstrong type holders and learned to grind them mostly using the full 15 deg. back rake, only with ground in chip breakers, ground on the corner of the wheel; these curled the chips and made them less dangerous to the operator than a simple top rake which had to have sufficient and appropriate feed to accomplish the same effect, they were simpler for the learner to control chips, but are easier to damage with their more acute cutting edge.


Thank you for an explanation that makes sense.


----------



## Wreck™Wreck (Jul 22, 2017)

If you insist on HSS tooling grind it however you want until it works .
All of the grinding how to guides and youtube videos are  general guidelines, this does not mean that grinding a tool this way will achieve your particular goals. As much as one may expect excellent results going by the book this is often not achieved.
Trial and error is how it is done, select a tool or grind that works for the particular job at hand.


----------



## benmychree (Jul 22, 2017)

Very articulate Mike; I fly more by the seat of the pants, but the way we grind tools is to get the results we want, I just go to the grinder and create a tool that I think will work best for me base on experience rather than theory; mostly as I have said, I avoid using much back rake because of its tendency to weaken the tool, but it is pretty much moot because most metal is removed by carbide inserts by hobby folk  and professionals alike.


----------



## Ken from ontario (Jul 22, 2017)

mikey said:


> I know your question pertains to back rake but no tool angle works in isolation and the rake angles are no exception. The rake angles are the most important angles on a turning tool because they have a tremendous impact on cutting forces and cutting temperatures. In fact, they are the key set of angles that change when a tool is ground for different materials. If you look at a turning tool angle table, you will see that the relief angles change a little for each material class but the rake angles are the main variables that allow the tool to work with different materials. As the tool cuts, it separates the chip along a plane called a shear plane and each material we turn has an optimal shear plane angle that clears the chip from the cut. This is why the rake angles change for each material. I will stop with the shear plane garbage now but just know that back rake shortens the shear plane and thereby reduces cutting forces significantly. You can grind a tool without back rake but your tool will cut with higher cutting forces than it should/could.
> 
> So, what does back rake actually do (aside from its impact on the chip)? Basically, it alters the direction and speed of chip flow and also determines where the cutting forces are directed.



Mike, I know I promised not to bother with the "why's  for now and only stick with the "how"s until I get comfortable with operating my mini lathe but the more I find out about the impact of cutting forces and cutting temperatures the more important it is to know why especially with  such small lathe so thanks for making it all clear enough to understand  and  so interesting .

All these youtube videos we watch could be a great source to educate ourselves but it could also be a source of confusion, I'm glad you are around to  clear up, define, and interpret  it all .


----------



## mikey (Jul 23, 2017)

benmychree said:


> Very articulate Mike; I fly more by the seat of the pants, but the way we grind tools is to get the results we want, I just go to the grinder and create a tool that I think will work best for me base on experience rather than theory; mostly as I have said, I avoid using much back rake because of its tendency to weaken the tool, but it is pretty much moot because most metal is removed by carbide inserts by hobby folk  and professionals alike.



I totally get what you're saying. You know how to grind a tool to do what you want on your lathe based on your experience so what works for you, works for you. Back rake, no back rake - if it works, that's what counts. 

For what it's worth, I simply wanted to help Ken understand one aspect of tip geometry to aid in his understanding of this complex subject. What I do encourage folks to do is grind tools with and without back rake (or any other tool angle) and come to their own conclusions. I have ground hundreds of tools, focusing on figuring out how each tool angle works and what it does. For me, this is not theory but I don't expect anyone to take my word for it; grind a tool and see for yourself.


----------



## Desolus (Jul 23, 2017)

Ken from ontario said:


> So it sounds like it is a personal preference to grind a back rake in the tool  and  not necessary .



I grind one for the sole purpose of chip controll.


----------

