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Models for grinding HSS Lathe Tools
- Thread starter mikey
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As you know, the thing with stainless is that it hardens with heat. It likes slightly larger relief angles so it doesn't rub and build heat. Side rake channels the chips out of the cut and the more side rake you have, the faster the chips leave. Since most of the heat in a cutting operation is carried out by the chip, you want the side rake angle to be as efficient as possible. Leaving a land between the cutting edge and side rake angle will reduce the cutting action of the tool, slow the chip flow and you'll build heat faster and the part will harden.
My suggestion is to increase relief by a few degrees, boost side rake a few more degrees and make them meet at the edge. It has been shown that tool life increases as side rake increases so boost side rake and create a sharp cutting edge.
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Thank you for your kind words, Tom. It's exciting to me that you guys are taking mere words and pictures and turning them into tools that help you in your work. It will be interesting when you start to design your own tools so they work the way you need them to. When that happens then you know you have it.
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Thanks. I think it works for me at work with heavy cut and flood coolant. Definitely will try these adjustments on my Atlas in the garage.
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The Knife Tool
The knife tool is a simple facing tool and it does that job extremely well. I made one many years ago and thought I invented something but then I read an article by Ian Kirby of the UK and discovered that it had been in use for some time … nothing new under the sun, I guess.
It turns out that our British cousins use the knife tool for a lot more than just facing; they turn and finish with it, too. You need a larger nose radius to turn with this tool. To finish, a small (1/32”) flat across the nose will create a nice finish. I tried knife tools configured this way but I prefer the Square Tool myself. Try it and see how you like it.
The knife tool is really stiff but also has a rather delicate tip that allows it to get into a tight corner and face out. The tip also allows you to chamfer inside or outside corners and grooves. But what the knife tool excels at is facing. It has a long, sharp edge that allows you to skim cut a face and leave a beautiful finish, better than any other tool I’ve seen. All you need to do is get the cutting edge just off parallel with the work, come into contact and face out.
When I need the work piece to have a shoulder that is a precise distance from the end of the work, this is the tool I use to face the shoulder to give me that distance. It will take a 0.0002” depth of cut and actually cut it. Most facing jobs are not precise but when you need precision, this tool will work for you.
The geometry of this tool is really simple. It has a 15° side and end relief angle; this greatly reduces rubbing and allows the tool to cut with very low cutting forces. It has 15° of side rake to enhance chip clearance; I chose this so it would work well with most materials, including Stainless Steel, and it does. Back rake is only 10° because I wanted the cutting forces focused at the side cutting edge, up close to the tip. If you take a light turning cut with this tool, you will see the chip come off near the tip of the tool as intended.
The nose radius on my personal tool is really small; I can see it but only if I look hard. I wanted a small nose radius so I could cut a corner with the smallest radius I could manage and it works well for that. Another reason for a small nose radius is to reduce radial cutting forces so that I can take really tiny sizing cuts on a thin work piece. As we all know, thin work pieces tend to deflect due to radial forces and a small nose radius really helps to reduce those forces. With this tool, I can take cuts small enough that the chips float away when the wind from my fan hits them. Your tool must be very sharp to do this but when I have to size a really small work piece, the knife tool is what I use.
My knife tools are made from cobalt HSS because it retains an edge longer. The one described above is for most stuff and I have another one for harder stuff; that one has 13° of side and end relief and 18° of side rake and 10° of back rake. The difference is to allow it to cut harder stuff and clear the chips faster to reduce work hardening. It doesn’t get used often.
Take the time to hone this tool well initially, then do this after every use and it will be ready when you need it. My tool will slice curlicues in newsprint.
There isn’t much more to say about this tool. You can also make a traditional facing tool. If you look closely at the traditional shape it is almost exactly like a knife tool without the bulk. The knife tool is much easier to grind so try one and see how you like it.
The knife tool is a simple facing tool and it does that job extremely well. I made one many years ago and thought I invented something but then I read an article by Ian Kirby of the UK and discovered that it had been in use for some time … nothing new under the sun, I guess.
It turns out that our British cousins use the knife tool for a lot more than just facing; they turn and finish with it, too. You need a larger nose radius to turn with this tool. To finish, a small (1/32”) flat across the nose will create a nice finish. I tried knife tools configured this way but I prefer the Square Tool myself. Try it and see how you like it.
The knife tool is really stiff but also has a rather delicate tip that allows it to get into a tight corner and face out. The tip also allows you to chamfer inside or outside corners and grooves. But what the knife tool excels at is facing. It has a long, sharp edge that allows you to skim cut a face and leave a beautiful finish, better than any other tool I’ve seen. All you need to do is get the cutting edge just off parallel with the work, come into contact and face out.
When I need the work piece to have a shoulder that is a precise distance from the end of the work, this is the tool I use to face the shoulder to give me that distance. It will take a 0.0002” depth of cut and actually cut it. Most facing jobs are not precise but when you need precision, this tool will work for you.
The geometry of this tool is really simple. It has a 15° side and end relief angle; this greatly reduces rubbing and allows the tool to cut with very low cutting forces. It has 15° of side rake to enhance chip clearance; I chose this so it would work well with most materials, including Stainless Steel, and it does. Back rake is only 10° because I wanted the cutting forces focused at the side cutting edge, up close to the tip. If you take a light turning cut with this tool, you will see the chip come off near the tip of the tool as intended.
The nose radius on my personal tool is really small; I can see it but only if I look hard. I wanted a small nose radius so I could cut a corner with the smallest radius I could manage and it works well for that. Another reason for a small nose radius is to reduce radial cutting forces so that I can take really tiny sizing cuts on a thin work piece. As we all know, thin work pieces tend to deflect due to radial forces and a small nose radius really helps to reduce those forces. With this tool, I can take cuts small enough that the chips float away when the wind from my fan hits them. Your tool must be very sharp to do this but when I have to size a really small work piece, the knife tool is what I use.
My knife tools are made from cobalt HSS because it retains an edge longer. The one described above is for most stuff and I have another one for harder stuff; that one has 13° of side and end relief and 18° of side rake and 10° of back rake. The difference is to allow it to cut harder stuff and clear the chips faster to reduce work hardening. It doesn’t get used often.
Take the time to hone this tool well initially, then do this after every use and it will be ready when you need it. My tool will slice curlicues in newsprint.
There isn’t much more to say about this tool. You can also make a traditional facing tool. If you look closely at the traditional shape it is almost exactly like a knife tool without the bulk. The knife tool is much easier to grind so try one and see how you like it.
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- Dec 20, 2012
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60° Threading Tool
My personal threading tools, a 3/8" Super-Mo-Max tool for larger threads on the left, a Rex AAA tool for smaller threads on the right.
This is just a standard threading tool, ground to an accurate 60° included angle at the tip. As noted, the tip is moved over to the left of the blank to allow you to get closer to a shoulder or thread relief before the shank of the tool hits it. You can grind it even closer by making the left side angle smaller.
This tool has 15° relief angles. It isn’t that I have a love affair with 15°; I actually ground tools with different relief angles to find one that cut clean threads without leaving all sorts of burrs or defects in the threads; 15° just happened to be the best of the lot, that’s all. This is a zero-rake form tool (just a fancy way of saying the top is flat) so it cuts with higher cutting forces but since we cut threads at low speed, it isn’t a hindrance. I grind a 1/64” flat at the tip; this is to keep the tip from cracking right off, which it will do if you don’t include it. This also forms a flat at the bottom of the thread, which is desirable.
When you grind this tool, grind it precisely and hone it just as precisely. Don’t forget to hone the top, too. You will be amazed at how much better your threads will look when the tool is razor-sharp.
If you only cut threads with the compound and do not feed straight in with the cross slide then you can grind 5° of side rake into the tool and it will cut easier, clear chips better and will be just as accurate.
Not much more to say about this simple but essential tool.
My personal threading tools, a 3/8" Super-Mo-Max tool for larger threads on the left, a Rex AAA tool for smaller threads on the right.
This is just a standard threading tool, ground to an accurate 60° included angle at the tip. As noted, the tip is moved over to the left of the blank to allow you to get closer to a shoulder or thread relief before the shank of the tool hits it. You can grind it even closer by making the left side angle smaller.
This tool has 15° relief angles. It isn’t that I have a love affair with 15°; I actually ground tools with different relief angles to find one that cut clean threads without leaving all sorts of burrs or defects in the threads; 15° just happened to be the best of the lot, that’s all. This is a zero-rake form tool (just a fancy way of saying the top is flat) so it cuts with higher cutting forces but since we cut threads at low speed, it isn’t a hindrance. I grind a 1/64” flat at the tip; this is to keep the tip from cracking right off, which it will do if you don’t include it. This also forms a flat at the bottom of the thread, which is desirable.
When you grind this tool, grind it precisely and hone it just as precisely. Don’t forget to hone the top, too. You will be amazed at how much better your threads will look when the tool is razor-sharp.
If you only cut threads with the compound and do not feed straight in with the cross slide then you can grind 5° of side rake into the tool and it will cut easier, clear chips better and will be just as accurate.
Not much more to say about this simple but essential tool.
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- Mar 9, 2011
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- 190
- Joined
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Model Tools – End Notes
Guys, I’ve given you just about everything I know about tool grinding. I’m sure I didn’t catch it all so if I missed something, please tell me so I can fix it. Some of what is in this thread may differ from what I’ve written in the past; this is because like you, I am still learning and still trying to improve. What I posted in this thread is my current practice, for whatever that is worth.
I want to briefly mention the various kinds of tool blanks available. I’m including this because when I started, I had no idea what was what, which was better for a given application or if cheap Chinese stuff was okay.
My personal practice is to use 3/8” blanks for everything. Keep in mind that I only have a Sherline and an Emco 11” lathe. I would use 3/8” tools up to a 13” lathe, then step up to ½” tooling on larger lathes. This has less to do with stiffness; these tools are damned stiff. It has to do with grinding times. ½” tools take me twice as long to grind and they aren’t any better performance wise; call me lazy.
For a budding tool grinder, I believe the first and best steel to learn with is mild steel keystock from the hardware store that is cut to the length of a tool bit. It is going to take a while for your brain and hands to coordinate their efforts to produce a lathe tool shape that actually looks like a lathe tool. My advice is to stay with keystock until you are totally comfortable that you can grind the shape and angles you want without any problems, then move on to M2 HSS. HSS requires more pressure to grind, and cobalt or tungsten steels will be even harder so don’t be in a rush. Grinding keystock will pay dividends, believe me. Okay, let’s move on to HSS.
I think of HSS as M2 or cobalt. M2 is your basic HSS without cobalt in the alloy. It is the cheapest tool steel, easiest to find and to grind and is the most impact resistant of the tool steels. M2 will handle almost all the common materials we use in the hobby shop – mild and medium carbon steels, aluminum, brass, plastics or wood. It is fairly abrasion-resistant and holds a keen edge. This should be your daily driver unless you're working with hard stuff.
When working with higher carbon steels, semi-hardened steels, stainless steels and other more unusual materials (Titanium), cobalt or tungsten HSS may be a better choice. I say “may” because most of these harder turning materials are usually machined with deep cuts at higher speeds and feeds. While these alloyed steel tool bits retain their hardness and edges at the higher temperatures these cutting conditions impose, whether your small hobby lathe has the power or rigidity to make the cuts required is another thing. Moreover, the higher temperatures that result from machining these materials can, and often does, result in work hardening and this can make taking accurate sizing or finishing cuts a challenge. This is why inserted carbide tooling is usually chosen when working with harder materials. So, why not just use carbide tooling for these materials? You can, if you have the speed and rigidity those tools require.
This is where being able to grind a custom tool comes into play. If you run a small lathe, the cutting forces and cutting temperatures will be quite high when machining harder materials if you use standard tip geometry, but if you were to grind a tool that reduces those forces and temperatures then your lathe will often perform much better. So, when we think of working with harder materials we do need to think about which tool material to use but we must also attend to the tip geometry of that tool; the smaller the lathe, the more important this becomes. Moving on …
In the non-M2 class, we have the Tungsten steels (the T-series of HSS) and the Molybdenum steels (the M-series HSS). Note that beyond the M2 steels, cobalt is added to the M-series alloys to provide its heat and abrasion resistant properties, while Tungsten is the key alloying material in Tungsten bits (they also have cobalt in them). There are actually 7 tungsten steels and 17 molybdenum/cobalt steels but most of them are specialty steels that you won’t see in the form of a square lathe tool bit. Between the two, the M-series is far more available.
Tungsten
The common grades you will see will be T4, T8 and T15 but rather than the alloy, they are usually labelled with some catchy name. Crucible was the main supplier of Tungsten HSS:
· Rex AAA = T4
· Rex 95 = T8
· CPM Rex T15 = T15
· Teledyne used to make the Vasco Supreme = T15; this is an outstanding tool bit if you can find them.
· I’m sure there are others that I don’t know about.
Molybdenum and Cobalt
· Cleveland Mo-max = M2. This is the highest quality M2 tool bit I know of. Most are made in Mexico now but older stock was made in the US and can still be found on eBay. The country of origin is printed on these bits and both work well.
· ETM HSS – M2 of consistent high quality. One of my favorites.
· Armstrong, Morse, Chicago-Latrobe are all good M2 HSS.
· Cleveland Mo-max cobalt = M35 cobalt or 5% cobalt
· Cleveland Super-Mo-Max = M42 cobalt or 8% cobalt
Some generic bits will be labelled “HSS-Co”. I do not know the content of these bits but they contain cobalt; could be 5%, 8%, whatever. I have used all those mentioned above and all are high quality. If I had to choose only one, I would choose the USA-made Mo-max M2 HSS for its consistent quality. For cobalt bits, I prefer the Super-Mo-Max bits but also like the tungsten-bearing Vasco Supreme and anything from Crucible.
So, what about tool bits from China, India, Poland, Japan or Israel? I have used some very high quality bits from Japan and Israel (TTC, the house brand from Travers) and they work great. Chinese bits vary in quality and most of them are not labelled; this makes it difficult to assess them. However, if I was a budding tool modifying monster, I would use Chinese import bits until I hit on a winner design, then make it from a known high quality blank.
Honing
I suggest using diamond stones to hone your tools with. I prefer the mono-crystalline stones from DMT but the poly-crystalline stones from EZ-Lap are okay. For most honing, I use the credit card sized stones in coarse, fine and extra-fine grits. You can use water as a lubricant. I recently discovered the wetting agent from Accu-finish and it works really well and stays on the stone longer.
I hone my tools after every use and oil them before storing. Sharp is good for turning tools and its nice when I pull a tool out and know that is honed and ready to go. Treated this way, a good HSS tool will last for well over a decade.
Let me end this by saying that a well-ground HSS tool is a joy to use. However, it is not the only tool to use. There are times when a brazed or inserted carbide tool will be better and you need to find out when that is. I would encourage you to grind conventional tools and then compare it to your carbide tooling and your modified HSS tools to see which are better for your needs. Keep an open mind about tooling; all are useful but only one will be the best for the job at hand – use that one.
Thanks for following along. I hope the model tools and the information in this thread is useful to you. Please post to this thread about your models or your own tools and experiences. I, for one, would like to see them. Again, if I missed anything or glossed over something that needs clarification, please let me know.
EDIT: I forgot to mention that when stoning on your nose radius, be sure you maintain the angle of the tool at the front. Stone a flat from top to bottom, then carefully round and blend it into the side and end faces. For your threading tools, you only need a flat; you do not need to round it. When deciding on nose radii, it is better to go small unless you need a better surface finish; don't forget that the bigger the nose radius, the higher the radial forces and deflection will be. By small, I mean 1/64" to 1/32". Look at a radius gauge in these sizes to get an idea of what you need and then just estimate it as you stone it on. You do not need to be precise in this but try to get close.
Mike
Guys, I’ve given you just about everything I know about tool grinding. I’m sure I didn’t catch it all so if I missed something, please tell me so I can fix it. Some of what is in this thread may differ from what I’ve written in the past; this is because like you, I am still learning and still trying to improve. What I posted in this thread is my current practice, for whatever that is worth.
I want to briefly mention the various kinds of tool blanks available. I’m including this because when I started, I had no idea what was what, which was better for a given application or if cheap Chinese stuff was okay.
My personal practice is to use 3/8” blanks for everything. Keep in mind that I only have a Sherline and an Emco 11” lathe. I would use 3/8” tools up to a 13” lathe, then step up to ½” tooling on larger lathes. This has less to do with stiffness; these tools are damned stiff. It has to do with grinding times. ½” tools take me twice as long to grind and they aren’t any better performance wise; call me lazy.
For a budding tool grinder, I believe the first and best steel to learn with is mild steel keystock from the hardware store that is cut to the length of a tool bit. It is going to take a while for your brain and hands to coordinate their efforts to produce a lathe tool shape that actually looks like a lathe tool. My advice is to stay with keystock until you are totally comfortable that you can grind the shape and angles you want without any problems, then move on to M2 HSS. HSS requires more pressure to grind, and cobalt or tungsten steels will be even harder so don’t be in a rush. Grinding keystock will pay dividends, believe me. Okay, let’s move on to HSS.
I think of HSS as M2 or cobalt. M2 is your basic HSS without cobalt in the alloy. It is the cheapest tool steel, easiest to find and to grind and is the most impact resistant of the tool steels. M2 will handle almost all the common materials we use in the hobby shop – mild and medium carbon steels, aluminum, brass, plastics or wood. It is fairly abrasion-resistant and holds a keen edge. This should be your daily driver unless you're working with hard stuff.
When working with higher carbon steels, semi-hardened steels, stainless steels and other more unusual materials (Titanium), cobalt or tungsten HSS may be a better choice. I say “may” because most of these harder turning materials are usually machined with deep cuts at higher speeds and feeds. While these alloyed steel tool bits retain their hardness and edges at the higher temperatures these cutting conditions impose, whether your small hobby lathe has the power or rigidity to make the cuts required is another thing. Moreover, the higher temperatures that result from machining these materials can, and often does, result in work hardening and this can make taking accurate sizing or finishing cuts a challenge. This is why inserted carbide tooling is usually chosen when working with harder materials. So, why not just use carbide tooling for these materials? You can, if you have the speed and rigidity those tools require.
This is where being able to grind a custom tool comes into play. If you run a small lathe, the cutting forces and cutting temperatures will be quite high when machining harder materials if you use standard tip geometry, but if you were to grind a tool that reduces those forces and temperatures then your lathe will often perform much better. So, when we think of working with harder materials we do need to think about which tool material to use but we must also attend to the tip geometry of that tool; the smaller the lathe, the more important this becomes. Moving on …
In the non-M2 class, we have the Tungsten steels (the T-series of HSS) and the Molybdenum steels (the M-series HSS). Note that beyond the M2 steels, cobalt is added to the M-series alloys to provide its heat and abrasion resistant properties, while Tungsten is the key alloying material in Tungsten bits (they also have cobalt in them). There are actually 7 tungsten steels and 17 molybdenum/cobalt steels but most of them are specialty steels that you won’t see in the form of a square lathe tool bit. Between the two, the M-series is far more available.
Tungsten
The common grades you will see will be T4, T8 and T15 but rather than the alloy, they are usually labelled with some catchy name. Crucible was the main supplier of Tungsten HSS:
· Rex AAA = T4
· Rex 95 = T8
· CPM Rex T15 = T15
· Teledyne used to make the Vasco Supreme = T15; this is an outstanding tool bit if you can find them.
· I’m sure there are others that I don’t know about.
Molybdenum and Cobalt
· Cleveland Mo-max = M2. This is the highest quality M2 tool bit I know of. Most are made in Mexico now but older stock was made in the US and can still be found on eBay. The country of origin is printed on these bits and both work well.
· ETM HSS – M2 of consistent high quality. One of my favorites.
· Armstrong, Morse, Chicago-Latrobe are all good M2 HSS.
· Cleveland Mo-max cobalt = M35 cobalt or 5% cobalt
· Cleveland Super-Mo-Max = M42 cobalt or 8% cobalt
Some generic bits will be labelled “HSS-Co”. I do not know the content of these bits but they contain cobalt; could be 5%, 8%, whatever. I have used all those mentioned above and all are high quality. If I had to choose only one, I would choose the USA-made Mo-max M2 HSS for its consistent quality. For cobalt bits, I prefer the Super-Mo-Max bits but also like the tungsten-bearing Vasco Supreme and anything from Crucible.
So, what about tool bits from China, India, Poland, Japan or Israel? I have used some very high quality bits from Japan and Israel (TTC, the house brand from Travers) and they work great. Chinese bits vary in quality and most of them are not labelled; this makes it difficult to assess them. However, if I was a budding tool modifying monster, I would use Chinese import bits until I hit on a winner design, then make it from a known high quality blank.
Honing
I suggest using diamond stones to hone your tools with. I prefer the mono-crystalline stones from DMT but the poly-crystalline stones from EZ-Lap are okay. For most honing, I use the credit card sized stones in coarse, fine and extra-fine grits. You can use water as a lubricant. I recently discovered the wetting agent from Accu-finish and it works really well and stays on the stone longer.
I hone my tools after every use and oil them before storing. Sharp is good for turning tools and its nice when I pull a tool out and know that is honed and ready to go. Treated this way, a good HSS tool will last for well over a decade.
Let me end this by saying that a well-ground HSS tool is a joy to use. However, it is not the only tool to use. There are times when a brazed or inserted carbide tool will be better and you need to find out when that is. I would encourage you to grind conventional tools and then compare it to your carbide tooling and your modified HSS tools to see which are better for your needs. Keep an open mind about tooling; all are useful but only one will be the best for the job at hand – use that one.
Thanks for following along. I hope the model tools and the information in this thread is useful to you. Please post to this thread about your models or your own tools and experiences. I, for one, would like to see them. Again, if I missed anything or glossed over something that needs clarification, please let me know.
EDIT: I forgot to mention that when stoning on your nose radius, be sure you maintain the angle of the tool at the front. Stone a flat from top to bottom, then carefully round and blend it into the side and end faces. For your threading tools, you only need a flat; you do not need to round it. When deciding on nose radii, it is better to go small unless you need a better surface finish; don't forget that the bigger the nose radius, the higher the radial forces and deflection will be. By small, I mean 1/64" to 1/32". Look at a radius gauge in these sizes to get an idea of what you need and then just estimate it as you stone it on. You do not need to be precise in this but try to get close.
Mike
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I just thought of one more tool that may be of interest to others and my self. how about a tool for a fly cutter? While not necessarily a lathe bit it could be useful information in the hobby shop if you have any insights on one. Seems about all the info I find is just a hint to grind as a left turning tool, how about how to make it better? This whole thread has been awesome and hopefully will be made into a sticky on here somewhere.
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