Thanks Z2V. I dont want to jack the thread but I think I saw a CTS-V in one of your photos earlier on in this thread? I think it was around page 4 or 5 that I saw the photo. I have almost read every page of this thread. I think I’m up to page 22. I am trying to absorb every bit of information from everyone that has posted here !
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Models for grinding HSS Lathe Tools
- Thread starter mikey
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First, thank you for your kind words, Brandon. We ALL stand on the shoulders of the guys who went before us, who shared knowledge freely and helped us along the way. You, me and the other guys on the forum all try to help when we can. Together, we can keep the hobby and HM healthy and growing.
Okay, before we get too far, you're using CRS. I assume you mean cold finished rod but I'm not clear which steel it is. CRS is usually used to describe CR1018, 1045, 1141, 1144 and there is even CR12L14. Clearly, there is a difference so which one are you using? Most CRS has a higher carbon content and greater density due to the forging it undergoes. While not as hard as tool steel, some of them can be considered semi-hard. The reason this stuff matters is because the tool differs for the kind of material you're turning; not so much the shape, but the angles. So, is there a tool that will work with all CRS AND tool steels like O-1/W-1? Yes, you can make a tool that will work with both, although there will be some compromises. I doubt you'll be able to tell the difference between a tool optimized for either group unless you were doing big runs of stuff.
Before we discuss tool angles, know that a knife tool works well for facing primarily or very light finishing cuts. As you've noticed, it is not intended to be a good turning tool. For that, a general purpose shape works much better and the reason is the end cutting edge on the general purpose tool. You'll note that while a knife tool has an end cutting edge, it doesn't really contact the work in use; all the cutting is done by the side cutting edge and the nose radius. A knife tool can take a big roughing cut but it won't finish well because there is no end cutting edge to provide the finish ... make sense? In contrast, a general purpose tool has a side cutting edge and nose radius that takes the bulk of the material off and an end cutting edge that shears a nice finish, and that is why it works better for turning! Who knew?
A general purpose tool like our square tool is a really good shape. It can rough, face or finish depending on the lead angle you use and it can turn into a shoulder, which makes it really useful for most lathe work. However, the relief and rake angles you use determines which material it will work well with. Fortunately, I've gone over most of this in this thread so I don't need to re-write it. What I will do is give you the angles you need for a tool that will work well with harder steels (1144, O-1) and you can read more about it in this thread for the rationale. I will use the shorthand we've unofficially developed here and that should be enough for you to grind the tool/tools you need.
As for the boring bar thing, let me PM you about that. I have something that should provide some food for thought.
Regarding the tool bits that are used either straight or angled at the end of a bar and held in place with a set screw, think about how the tool contacts the work. What you have is essentially the same as a left hand turning tool moving into the work, right? So, just grind the tip like a LH lathe tool will look and it will work just fine; trust me, it will work. For a general purpose tool that will cut most stuff, grind a LH square tool shape at the end of the blank.
As for the brazed carbide tool used in a fly cutter, any LH turning tool will work but try to choose one with the side cutting edge angled back a bit. This is called a BL tool and the angled side cutting edge enters the work gradually, which is good for the interrupted cuts encountered when fly cutting. If you can, use one made with C5 for steel. It will look like this:
Put a small nose radius on it with a diamond stone and it will work okay for you. If you choose to grind a HSS tool, do as @ttabbal said and try a LH square tool with a 1/32" nose radius; bet it will finish better than that carbide tool.
Your lathe sounds like a good one, Brandon, and you have the experience to use it. I have no doubt it will work with carbide or HSS tooling and there is room for both. You already know how to use carbide. Learn to grind HSS so you have the option.
Okay, long post but I think I covered most of the points. If I missed something important, point it out so I can address it.
Okay, before we get too far, you're using CRS. I assume you mean cold finished rod but I'm not clear which steel it is. CRS is usually used to describe CR1018, 1045, 1141, 1144 and there is even CR12L14. Clearly, there is a difference so which one are you using? Most CRS has a higher carbon content and greater density due to the forging it undergoes. While not as hard as tool steel, some of them can be considered semi-hard. The reason this stuff matters is because the tool differs for the kind of material you're turning; not so much the shape, but the angles. So, is there a tool that will work with all CRS AND tool steels like O-1/W-1? Yes, you can make a tool that will work with both, although there will be some compromises. I doubt you'll be able to tell the difference between a tool optimized for either group unless you were doing big runs of stuff.
Before we discuss tool angles, know that a knife tool works well for facing primarily or very light finishing cuts. As you've noticed, it is not intended to be a good turning tool. For that, a general purpose shape works much better and the reason is the end cutting edge on the general purpose tool. You'll note that while a knife tool has an end cutting edge, it doesn't really contact the work in use; all the cutting is done by the side cutting edge and the nose radius. A knife tool can take a big roughing cut but it won't finish well because there is no end cutting edge to provide the finish ... make sense? In contrast, a general purpose tool has a side cutting edge and nose radius that takes the bulk of the material off and an end cutting edge that shears a nice finish, and that is why it works better for turning! Who knew?
A general purpose tool like our square tool is a really good shape. It can rough, face or finish depending on the lead angle you use and it can turn into a shoulder, which makes it really useful for most lathe work. However, the relief and rake angles you use determines which material it will work well with. Fortunately, I've gone over most of this in this thread so I don't need to re-write it. What I will do is give you the angles you need for a tool that will work well with harder steels (1144, O-1) and you can read more about it in this thread for the rationale. I will use the shorthand we've unofficially developed here and that should be enough for you to grind the tool/tools you need.
- Shape: I would recommend a general purpose shape, just like our model square tool.
- Relief angles, both side and end: If you look at a tool grinding table, you will see that the relief angles for machine steels and tools steels is about 10 degrees. To reduce cutting forces without sacrificing edge life too much, I would suggest using 12 degree relief angles for both side and end. This means that you will angle your tool rest to 12 degrees (instead of 15 degrees for a square tool) and grind the side and end cutting edge angles without changing the tool rest angle.
- Side rake: To reduce cutting forces and keep temps lower, I would use 16 degrees of side rake instead of the recommended 12 degrees. While a 4 degree change might seem small, it will reduce cutting forces significantly, especially when combined with increased relief angles. Moreover, it will not impact on edge life much at all and will reduce the tendency to work harden the material. This matters a lot because high carbon steels like to work harden on you if local temps at the point of cut get too high. Increasing side rake will get the chips out faster, thereby lowering the temp at the point of cut.
- Back rake: Depending on which steel you're turning, back rake can really vary. However, a reasonable back rake would be around 14-16 degrees (I would use 15 degrees). This will put the cutting forces near the tip, accelerate chip flow, thin the chip and enhance finishes ... all in one single angle change.
- Nose radius: I highly recommend you use a 1/64" nose radius. Going bigger will only increase deflection in harder steels and with the amount of back rake on this tool, it will still finish nicely.
As for the boring bar thing, let me PM you about that. I have something that should provide some food for thought.
Regarding the tool bits that are used either straight or angled at the end of a bar and held in place with a set screw, think about how the tool contacts the work. What you have is essentially the same as a left hand turning tool moving into the work, right? So, just grind the tip like a LH lathe tool will look and it will work just fine; trust me, it will work. For a general purpose tool that will cut most stuff, grind a LH square tool shape at the end of the blank.
As for the brazed carbide tool used in a fly cutter, any LH turning tool will work but try to choose one with the side cutting edge angled back a bit. This is called a BL tool and the angled side cutting edge enters the work gradually, which is good for the interrupted cuts encountered when fly cutting. If you can, use one made with C5 for steel. It will look like this:
Put a small nose radius on it with a diamond stone and it will work okay for you. If you choose to grind a HSS tool, do as @ttabbal said and try a LH square tool with a 1/32" nose radius; bet it will finish better than that carbide tool.
Your lathe sounds like a good one, Brandon, and you have the experience to use it. I have no doubt it will work with carbide or HSS tooling and there is room for both. You already know how to use carbide. Learn to grind HSS so you have the option.
Okay, long post but I think I covered most of the points. If I missed something important, point it out so I can address it.
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- Dec 20, 2012
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Sorry, missed this one.
I use a Tormach Superfly that uses positive rake inserts - SEHT1204AFFN-X83 for aluminum and SEHT1204AFSN-X45 for steels.
I also use a Sherline inserted carbide flycutter that takes CPMW 3251 inserts on my Sherline mill and my RF-31 mill. Leaves an incredible finish and is essentially a single insert face mill. Love this tool!
So do I, believe me. Every single person here does something for a living and many are experts in their respective fields that usually just happens not to be machining. It is the height of arrogance to speak to anyone here with disrespect just because you are a machinist or know more about it than they do; in their own field, they would kick your butt! I respect every single member here, every one.
And then there are the guys like RJSakowski that blows you away with his understanding of physics and chemistry, or Mark Jacobs when discussing VFD's or Bob Korves and shapers or Tony Wells and the other pro machinists who offer sage advice to keep us grounded. So many smart, talented people here and yeah, I happily learn from them every day and am grateful for the opportunity.
I was eagerly awaiting your thoughts on this!
maybe you would send me the PM too as I need to equip myself for the Criterion head I bought.I was eagerly awaiting your thoughts on this!
After reading and thinking, and talking with @mikey, I bit the bullet and picked up a set of Borite Cobalt bars. BH500 for 1/2" shank bars. Not cheap, but very good quality. I figured I bought a nice boring head, might as well get quality bars.
If you want to try them, LMS sells a similar looking import set. I can't say anything about them as I haven't used them. The cost difference wasn't enough for me to pass up known quality.
The brazed carbide import sets are everywhere and cheap. From what I have read, a lot of people hate them though.
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The biggest problem with the brazed import boring bars is that they are often not ground correctly. The carbide itself may not be top notch, but it is quite useful, in my experience. The grind looks OK at first glance, but often the clearance angles are not correct, making them rub on the work instead of cutting, especially in minimum diameter holes for the size of the bar. Those issues can be pretty easily corrected with a proper grind for the work at hand, but grinding and honing tools capable of handling carbide and leaving proper geometry and a nice sharp edge are needed, along with operator skill, to make them correct. Some of us don't want to mess with that, and want perfect tools out of the box, which is fine, but leads to throwing them away when dull, using them when dull, or regularly buying new ones, which can get pricey for quality bars. Which brings us back to the reason for this thread of 785 posts so far -- we need to know how to do it ourselves, and then we can simply (and proudly) do it ourselves!
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Well said, Bob, very well said.
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There are all kinds of boring bars, both commercial and shop-made. I've tried most kinds - brazed carbide, inserted carbide, cobalt, HSS, commercial cobalt, commercial HSS and home-ground HSS on both the lathe and in a boring head. After awhile, you sort of come to some personal conclusions for what works for you and what doesn't, and it won't necessarily agree with what others found for themselves.
When it comes to boring, I hate boring something twice. I want it on size with straight walls and a clean finish the first time. I find that I get these results on the lathe most easily and often when I use carbide shanked bars, either inserted tip for larger and deeper holes or solid carbide bars for smaller holes.
On the mill, them danged centripetal forces influence my tooling choices. I find that at the speeds I can run with the mills I have, carbide is not a good choice because I can't run slow enough and still get a really nice finish. If I run fast enough for a good finish, I get too much vibration. Cobalt bars, on the other hand, finish really nicely. They are very sharp and bore accurately at the low speeds I can run at so, for me, this works the best. There are work-arounds for dealing with centripetal forces; I just have to get off my lazy butt and do it. In the meantime, Borite cobalt bars work for me so I'm with @ttabbal on this one.
I do admit that those cheapy Chinese brazed carbide bars come in handy in a boring head or the lathe on occasion. If you get and keep them sharp as Bob said, they actually work rather well. They will not finish as well as a good bar but for rough work they actually do better than a $10.00 set has any business doing. If I was a new guy, I would buy a set of these tools and spend some time with a diamond stone to sharpen and hone them, then learn to bore with them. The shanks of these tools may be either too soft or too hard but they will still teach the fundamentals of boring quite well.
When it comes to boring, I hate boring something twice. I want it on size with straight walls and a clean finish the first time. I find that I get these results on the lathe most easily and often when I use carbide shanked bars, either inserted tip for larger and deeper holes or solid carbide bars for smaller holes.
On the mill, them danged centripetal forces influence my tooling choices. I find that at the speeds I can run with the mills I have, carbide is not a good choice because I can't run slow enough and still get a really nice finish. If I run fast enough for a good finish, I get too much vibration. Cobalt bars, on the other hand, finish really nicely. They are very sharp and bore accurately at the low speeds I can run at so, for me, this works the best. There are work-arounds for dealing with centripetal forces; I just have to get off my lazy butt and do it. In the meantime, Borite cobalt bars work for me so I'm with @ttabbal on this one.
I do admit that those cheapy Chinese brazed carbide bars come in handy in a boring head or the lathe on occasion. If you get and keep them sharp as Bob said, they actually work rather well. They will not finish as well as a good bar but for rough work they actually do better than a $10.00 set has any business doing. If I was a new guy, I would buy a set of these tools and spend some time with a diamond stone to sharpen and hone them, then learn to bore with them. The shanks of these tools may be either too soft or too hard but they will still teach the fundamentals of boring quite well.
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This thread is really great. The only problem is that it has become so large that it is unwieldy to use and hard to find stuff. One thing that I would find to be very usable is if there could be one place on the forum where the basic information in this thread could be presented. I am thinking of drawings, not pictures, of the different types of tool bits with the angles for the tool. My lathe came with a chart to be mounted on the wall for quick reference for the basic tool bits. It really helped me with grinding tool bits. I couldn't scan the entire chart do to it's size. A portion of the chart is attached.
I would be willing to do the drawings. I use google sketchup for drawing. Sketchup drawings are 3D that I would then convert into a jpg showing top, bottom, side and front views that could be uploaded to the forum.
No forum that I have been on allows sketchup drawings to be uploaded. If the actual sketchup drawing could be uploaded then the drawing could be viewed in sketchup where you could rotate and spin the drawing to whatever angle you wanted for viewing. Sketchup is a free program.
Just a suggestion.
I would be willing to do the drawings. I use google sketchup for drawing. Sketchup drawings are 3D that I would then convert into a jpg showing top, bottom, side and front views that could be uploaded to the forum.
No forum that I have been on allows sketchup drawings to be uploaded. If the actual sketchup drawing could be uploaded then the drawing could be viewed in sketchup where you could rotate and spin the drawing to whatever angle you wanted for viewing. Sketchup is a free program.
Just a suggestion.
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This thread has sort of taken on a life of its own and has become OUR thread, not MY thread. That has been really cool to watch and I couldn't be happier. However, it is huge and I agree that finding specific information can be tedious. Luckily, @DHarris did a Word Doc containing the gist of it. If you would like to compile a set of drawings that you can add here then that would make this thread a really nice resource. Or you can compile it and put it into the downloads section for guys to access. Either way, I think its a great idea and thank you for the offer!