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Models for grinding HSS Lathe Tools

Z2V

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Hey Guys
I just went in the garage and made a tool based off what Mike has already posted and I can say this tool cuts better than anything I have used on my little Craftsman lathe. I was able to make deeper cuts than before and with a much better finish. And this was my first try at doing it Mikes way!! I might try his knife tool latter this evening also.
Thanks Mike!!
 

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mikey

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Hey Guys
I just went in the garage and made a tool based off what Mike has already posted and I can say this tool cuts better than anything I have used on my little Craftsman lathe. I was able to make deeper cuts than before and with a much better finish. And this was my first try at doing it Mikes way!! I might try his knife tool latter this evening also.
Thanks Mike!!
Impressive, Jeff! Most guys have trouble grinding rake angles but you did it perfectly. I wonder if I could have done a better job myself!

Glad the tool works for you. Interesting what a few more degrees of angle can do, eh?
 

Aaron_W

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Good question, Aaron. Just scale it down proportionally. The side and end cutting edge angles do not need to be precise. When I grind tools, I don't measure anything or use lines. I used them here so other folks are able to reproduce the models. It isn't that shape is not important; it is. But you do not need to be precise about the shape. The angles are another thing and that you do need to get right.
Thank you, it just had me wondering since the pre-made tools I have don't go much beyond 1/4" of cut away except for the boring bar.

Trying to absorb your instructions, there is a lot there. You are doing a good job explaining though, I think when I finally have the chance to try this myself in a month or two it will make even more sense to me.
 

Metal

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3dp examples came out good, they aren't 100% accurate but the labels turned out readable and give a good idea of what the finished product should look like

well they would be at least if I didnt print them in black, hah.
 

Z2V

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I was able to make the knife tool tonight and I can say it delivered as promised. These tools have both been really easy to grind. Following Mikes directions, I don't see how I could screw it up. I wanted to make the threading tool also but just as I was finishing the knife tool a bearing in my bench grinder started raising all kinds of hell. I'll fix that Monday.
I'm supposed to be selling my lathe in the morning and was wanting to provide the new owner with a set of these tools. I guess two out of three will have to work for him.
I've tried a few times to grind tools freehand with miserable results. I made myself a good adjustable tool rest for my grinder and that made all the difference.
 

mikey

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I was able to make the knife tool tonight and I can say it delivered as promised. These tools have both been really easy to grind. Following Mikes directions, I don't see how I could screw it up. I wanted to make the threading tool also but just as I was finishing the knife tool a bearing in my bench grinder started raising all kinds of hell. I'll fix that Monday.
I'm supposed to be selling my lathe in the morning and was wanting to provide the new owner with a set of these tools. I guess two out of three will have to work for him.
I've tried a few times to grind tools freehand with miserable results. I made myself a good adjustable tool rest for my grinder and that made all the difference.
Jeff, I have to show Bonehead your post. He told me that, "... suck is contagious, you know ..." but now I have proof that isn't! Glad it worked out.

Please keep us posted.
 

Aukai

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Jeff, I have to show Bonehead your post. He told me that, "... suck is contagious, you know ..." but now I have proof that isn't! Glad it worked out.

Please keep us posted.
Good job, hope to be able to do as well. Yeah, yeah, OK what else is on the lift, besides the tool?:encourage::D
 

Z2V

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14 CTS-V on top and 13 ATS on bottom. Only way I can get two cars in a less than two car garage with a beer box, tool box, knee mill, lathe, 7-1/2 hp/ 80 gal air comp.,water softener, treadmill transformed into metal buffing/grinding table, lawn mower, etc, every square foot has purpose .
The tools are EASY to grind, get the angles right and just take it slow and easy. The suggested wood stick works well also. I used a piece of plywood I had close but I will dig around in my pile and find some oak when I have time.
 

mikey

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General Purpose Turning Tool

I’ve already discussed what this tool does and pretty much how to grind it. With all we’ve discussed and my other articles, grinding a tool should be pretty old hat by now. In deference to Tweinke, I will just show how a left hand turning tool would be laid out. The grinding is the same – just grind to the lines. The rake angles would be the same but ground on the other side of the belt or wheel vs a RH tool. So, a mirror image of a RH tool.

IMG_5655.jpg

Before I can explain why the Square Tool is ground the way it is, I have to briefly discuss cutting forces and how an angle table is used so that it makes sense.

Cutting Forces
There are actually three cutting forces in play whenever a tool comes in contact with a work piece. They are Tangential forces, Radial forces and Axial or Feed forces. I blatantly stole an image off the net because I’m too lazy to draw my own:

Screen Shot 09-20-17 at 05.05 PM.PNG


Tangential
forces (Fc in the pic) push down on your lathe tool when the tool is buried in the cut. They comprise about 75% of the sum of all the forces your tool experiences so anything that reduces or mitigates this force is a good thing.

Radial forces (Fr in the pic) push the tool out of the cut at a 90° angle. They are about 1/3 – ¼ the magnitude of Tangential forces but they matter because this is what causes deflection. Since the turning tool is somewhat rigidly mounted and is mostly non-compressible, Radial forces will cause the work piece to flex away from the tool instead. Our goal is to reduce this force to the extent we can to improve accuracy.

Axial forces are feed forces (Ft in the pic). In general, axial forces do not directly affect the cut. As the tool moves toward the chuck, the forces it encounters are these feed forces.

Each cutting force can actually be measured with strain gauges attached to the tool but I don’t own any. When I experimented with this stuff over 20 years ago, all I had was an ammeter hooked up to the motor of my lathe. My theory was that as I altered each angle of a turning tool, it would alter the cumulative cutting forces and I would be able to see a change in the motor load. I admit this is a really crude and insensitive set up but it was all I had at the time. Sadly, I lost the numerical data but I remember the results and here is what I think I know:
  • Cutting conditions matter. Assuming that motor load implies a change in cutting forces, as depth of cut and feed rate increase, cutting forces go up. As cutting speed increases, forces actually go down.
  • Increasing the relief angles reduces cutting forces. The more relief angles increase, the lower the forces. However, this also weakens the cutting edge so changes here must be conservative.
  • Increasing side rake reduces cutting forces more than increasing relief angles does. [It does this by shortening the Shear Plane length. The Shear Plane is an actual plane that extends at a 90° angle from the cutting tip through the thickness of the chip. As the Shear Plane length gets shorter, cutting forces go down, and vice versa.]
  • Increasing back rake reduces cutting forces (same Shear Plane nonsense) but less than increasing side rake does.
    o Back rake has more of an impact than you might think. If you look at the tool from the front you can see that the included angle at the side cutting edge is comprised of the side relief and the side rake angles. If you look at the tool from side you can see that the end relief and the back rake form another cutting edge, the end cutting edge. Alterations to either rake angle alters Shear Plane length so both impact on cutting forces.
    o Back rake also shifts the focus of cutting force concentration. In general, cutting forces will run perpendicular to the side cutting edge. This is reflected by the direction of chip flow. If you look at a tool ground with relief and side rake angles only, the chips will flow perpendicular to the side cutting edge. Now, when you add back rake you are adding that second included angle at the front end of the tool and that changes the focus of the forces. Now the chip flow direction is no longer perpendicular to the side cutting edge; it angles down and away from the tip of the tool. As back rake increases, the point where the chip leaves the work piece shifts closer and closer to the tip of the tool and when that happens the finish improves. Moreover, if you look carefully, you’ll see that chip flow rate actually increases and the chip thins out.
So, let’s summarize this into something useful:
1. Increasing the relief angles reduces cutting forces. It also improves finishes because it reduces rubbing under the side cutting edge. Increasing relief angles removes support under the cutting edge; use restraint when the tool will see high cutting loads.

2. Increasing side rake reduces cutting forces more than increasing relief angles. As side rake increases, chip flow accelerates. Since much of the heat in a cutting operation is retained in the chip, increasing side rake also reduces cutting temperatures.

3. Increasing back rake reduces cutting forces but less than changes in side rake does. It accelerates chip flow so it also contributes to cutting temperature reduction. It also changes the focus of cutting force concentration and improves finishes.

4. As cutting speed increases, cutting force magnitude decreases. This is useful, especially in harder materials. When you’re trying to come in on size, take a lighter depth of cut and increase speed and this will reduce Radial forces so there is less deflection. The tool cuts with greater ease and more accuracy.

You can use this information to modify any turning tool should you decide to do so. I’ll show you how to apply it shortly.

The Angle Table
In general, what defines the function of a lathe tool is its shape. How well it works and the material it works with is dependent on the angles the tool is ground with. If you look at a lathe tool angle table, you will see that the angles are material-specific.

angle table.png

The table angles define the tip geometry of a conventional lathe tool. You would choose a shape for your tool and then set your tool rest to grind the side and end (front) relief, then re-set the table for your side rake and angle the tool at your back rake angle and then grind both features at the same time. Each angle would change as you grind tools for each material type. The table is simple and easy to use.

When these tools are used on a larger lathe as they were intended, they work well. Unfortunately, when the same tool is used on a smaller, lighter, less rigid and less powerful lathe, they can produce cutting forces that may be excessive. If this is an issue for you then you might consider altering the geometry of your tools.

There is nothing sacred about these tables and there are no rules or laws that say you must grind your tools to these parameters. I don’t, and I don’t think you have to, either. However, the table is still useful because it gives us baseline values that we can modify to create a tip geometry that is more useful to us. We’ll get to this shortly but let me explain why the Square Tool is designed the way it is.

The design of the Square Tool is a compromise that allows it to work with multiple materials and with the lowest cutting force production I could manage. If you look at the angle table above, you will see that, on average, side relief is around 10-12°, end relief is 8-10° but the rake angles are all over the place. In order to reduce cutting forces, I increased the side and end relief angles to 15°; this is enough to lower forces but not enough to significantly reduce edge life. I settled on 15° of side rake because my tests showed that it resulted in a significant reduction in cutting forces but going beyond 20° seemed to increase edge wear more than I wanted, especially in medium carbon steels. I settled on 15° of back rake because this also reduced forces but more importantly, it shifted those forces just to the left of the tool tip. If you take a big cut with this tool, you’ll see the chip curling just to the left of the nose radius. This matters because this tool must be able to rough well but the tool also finishes pretty nicely. Placing the cutting force focus near the tip also allows the tool to face well because this is where a facing tool cuts.

Fooled you, eh? I bet you thought the 15° angle thing was just so I could give it a snazzy name like Square Tool – nope, not the case. It does work well with most common shop materials, so much so that I use it for most things except harder materials and stainless steel. This tool reduces cutting forces enough to enable my little Sherline lathe to at least double its depth of cut when compared to a conventionally ground tool so it does what it is designed to do. If you choose to reproduce it, I hope it works as well for you.

Modifying Your Tools

I’ve already written most of this stuff elsewhere but I’ll try to solidify it with a few examples. Say we want a general purpose turning tool for stainless steel. Whenever you need to cut something, you have to know the general machining properties of that something because this influences your tool angles. There are many formulations of stainless steel and I’ve only worked with 303, 304, 316L and 416. None of these is especially hard as supplied but they do work harden readily; dwell in a cut for too long and it gets hard enough to make you wish you were using a carbide tool.

Let’s decide that we’ll use our general purpose shape and that we want to accomplish two major things with our angles. First, we want to reduce cutting forces so that the tool cuts more freely, and secondly we want to prioritize cutting temperature reduction. Both goals are aimed at minimizing work hardening so we can come in on size. Having a nice finish would be nice as well.

The standard relief angle for SS is 10° but 12-13° would reduce cutting forces without affecting edge life too much. Standard side rake is 15-20° but I would take it up to 25° to reduce cutting forces, improve chip evacuation and keep cutting temps low. Standard back rake is 8° and here we need to make a choice. If we leave back rake at baseline then the tool will focus the cut at the side cutting edge. If we increase it, the tool will cut more freely and may finish better but may not be able to rough as well. In cases where I need to push the tool fairly hard, I try not to boost back rake too much so I would opt to increase back rake only a few degrees – maybe 10° max. You might think this won’t do anything but remember that the effect of these angle changes is cumulative; it will make a difference.

I would also keep the nose radius on the smaller side – 1/64” or so. The reason is to minimize radial forces. Why is it important for this tool? Because high radial forces will increase deflection and when the tool deflects it doesn’t cut and when it doesn’t cut, it builds heat.

You should know that the nose radius on any cutting tool has a big influence on radial forces; the larger the radius, the larger the radial forces. In general, radial forces will increase until the depth of cut exceeds the nose radius. Once the nose is buried in the cut where it is fully supported then radial forces tend to stabilize. It follows that the smaller the nose radius, the sooner it gets buried and supported so try to keep your nose radii on the smaller side when cutting hard stuff or stuff that work hardens.

This is getting to be a long post but let’s quickly look at a general purpose tool for aluminum. The Square Tool will work but not as well as a tool optimized for the material.

We can see that standard relief angles are 12 and 8 for the side and end. Since aluminum is fairly soft, we can easily increase both to 15° without endangering the edges. Side rake is already at 18°, which is a pretty healthy amount so I would leave it as is and boost back rake. Standard back rake is already huge at 35° but by increasing it to 40° we do several things: we reduce cutting forces, we focus all the cutting at the very tip of the tool to enhance finishes and we greatly accelerate chip flow to reduce cutting temperatures (because aluminum gets gummy when it heats up). Nose radius can be a bit larger, no more than 1/32”, and it will finish very well.

I have a tool ground exactly like this, with the same reasoning, and it will easily take a 0.25” deep cut on my 11” lathe. I know for sure it will go a lot deeper but I haven’t needed to waste material or prove the tool; it works for me. It has never developed a built up edge if I use WD-40 to lube the cut and the chips flow right off the tip as you would expect. It produces a near mirror finish when roughing and a mirror finish when finishing. It cuts with very little radial deflection so what you dial in is usually what you get. If you must take a lot off the diameter of a work piece, dial in a heavy cut and increase feed. This tool will create chips, not stringers, under those conditions and the tool will cut with minimal effort. You might give this one a try.

Okay, so that is the “how” of tool mods. Learn about your material then choose which angles to change to accommodate it. How much to change an angle is a guess but I try to keep them conservative, about 25-40% more than the baseline angle. In most cases, this only amounts to between 2-5° per angle but the changes are cumulative and a little bit can go a long way. You need to try this process to get a feel for it.

How do you tell if your geometry changes actually do something? What I do is grind a tool to the standard angles and see how it works. Then I grind a second tool to standard angles and then I modify one angle and assess. Then I change another angle and reassess. I keep this up until I’ve modified all the angles I want and then I focus on optimizing the amount of angle change. Maybe a degree more side rake will help, or a bit more back rake may improve the finish. The only way to know is to try it and see. When I have the tool cutting exactly the way I want it, I grind a keeper from a blank I trust.

This is already incredibly long and I’m repeating what I’ve said elsewhere but of all the tools you will grind, your general purpose tools will be the most useful. Now you know how to grind it, how to modify it, how much to change it and how to assess it.

You can take it from here.











 

Fallriverbryan

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One of my concern is where our relief angles meet. Actually, I have started using Fusion 360 so hopefully I will be able to include a diagram to illustrate my point but I will try and explain. I work with stainless, I grind to hold the edge, I don't grind my side rake all the way to the cutting edge. I leave 1/32 inch of 0 degree side rake angle. Is that the proper way or is that a mistake?

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T Bredehoft

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I just went in the garage and made a tool based off what Mike has already posted and I can say this tool cuts better than anything I have used on my little Craftsman lathe. I was able to make deeper cuts than before and with a much better finish. And this was my first try at doing it Mikes way!! I might try his knife tool latter this evening also.
Thanks Mike!!
Jeff, and Mike, I had exactly the same experience. I worked as a tool & die maker for 29 years, always used carbide tooling. Mike's explanations are the first real inkling I had as to tool geometry.
Thanks, Mike for the lessons, thank's Jeff for sharing your experience with us.
 

mikey

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One of my concern is where our relief angles meet. Actually, I have started using Fusion 360 so hopefully I will be able to include a diagram to illustrate my point but I will try and explain. I work with stainless, I grind to hold the edge, I don't grind my side rake all the way to the cutting edge. I leave 1/32 inch of 0 degree side rake angle. Is that the proper way or is that a mistake?

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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.
 

mikey

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Jeff, and Mike, I had exactly the same experience. I worked as a tool & die maker for 29 years, always used carbide tooling. Mike's explanations are the first real inkling I had as to tool geometry.
Thanks, Mike for the lessons, thank's Jeff for sharing your experience with us.
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.
 

Fallriverbryan

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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.
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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mikey

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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.
 

mikey

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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.

IMG_5656.jpg

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.
 

Rockytime

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You can see my grinder and tool rest here: http://www.machinistblog.com/modifying-a-craftsman-2-x-42-inch-belt-sander-for-tool-grinding/#more-5349.

Hi Mikey, FYI I just purchased the Craftsman 6" disk and 1x72 belt 1/2 hp sander. I think I paid a little more than I should have on fleabay but it is certainly sturdy and runs well. Only modification will be a new table. I grind nothing over 1/4" and quire a bit smaller. Wood gouges sharpen on a 4" sander. Now for new belts. Thanks for showing your mods.

Regards, Les
 

mikey

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Awesome, Les! The 1/2hp models are rare, even the 1" belt models. I hope it works as well for you as mine does for me. Keep us posted!
 

mikey

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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
 
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tweinke

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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.
 

mikey

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I don't know what the other guys think but I can give you my take on a flycutter tool. I used to grind a left hand roughing shape with a fairly generous nose radius - slightly larger than 1/32". I wasn't too deep into tool modifying back then but I wasn't too thrilled about tool life, although the finish was really good. When doing harder materials, I could go through three tool bits just squaring a work piece made of stainless steel. Then I discovered Sherline's inserted carbide flycutter that had a much longer work life and never looked back.

Knowing what I know now, here is what I would try if I were to grind a flycutter bit:
  • Almost every cut will be an interrupted cut so I would only use M2 HSS; cheaper, more impact-resistant, fast to grind.
  • For a shape, I would grind a roughing tool shape or possibly a general purpose shape like our square tool. Depending on depth of cut, cutting loads may be very high.
  • Flycutters run at high speed, which lowers cutting forces so we can afford to keep relief angles near baseline levels for strength.
  • Since the relief angles are stronger, we could afford to increase side rake to boost chip clearance and lower forces more so I would go maybe 4 degrees above baseline.
  • Almost all cutting is at the tip so I would boost back rake by 5 degrees and this will put all the cutting action at the tip.
  • Then I would grind a nose radius just a tad bigger than 1/32".
I'm pretty convinced that a LH Square tool would work pretty good if you gave it a slightly larger nose radius. The only way to know is to try it. Of course, you would change the side cutting edge angle of the tool to be sure the nose was the contact point but that's pretty simple to do.

Dunno' ... what do you think? Why not make a LH square tool and try it, then report back and we can brainstorm on it.
 

tweinke

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Next time I'm in the shop with a fly cutting tool job I will definitely give that a try!
 

IanT

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Hi Mikey,

A very interesting set of posts but I do have a question about 'relief' angles (I tend to call them clearance). My understanding has always been that the relief angles are exactly that - they provide sufficient 'clearance' to stop the tool rubbing on the work. I also understand that if the relief angle is increased the 'lip' angle is decreased and the cutting edge thereby weakened. But I'm not sure how changing the relief angle improves the 'sharpness' of the tool - that to my mind is a matter of the amount of rake applied (be that side and/or back).

I routinely use the wheel periphery to give clearance to my tools - and the slight curve imparted also helps when stoning the top edge. I do vary the rake(s) used, dependant on material to be cut but not the clearances. I have a mental picture of how this all works but cannot quite see how more relief makes for better cutting? Surely there is either sufficient clearance or there is not?

Regards,

IanT
 

mikey

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Hi Mikey,

A very interesting set of posts but I do have a question about 'relief' angles (I tend to call them clearance). My understanding has always been that the relief angles are exactly that - they provide sufficient 'clearance' to stop the tool rubbing on the work. I also understand that if the relief angle is increased the 'lip' angle is decreased and the cutting edge thereby weakened. But I'm not sure how changing the relief angle improves the 'sharpness' of the tool - that to my mind is a matter of the amount of rake applied (be that side and/or back).

I routinely use the wheel periphery to give clearance to my tools - and the slight curve imparted also helps when stoning the top edge. I do vary the rake(s) used, dependant on material to be cut but not the clearances. I have a mental picture of how this all works but cannot quite see how more relief makes for better cutting? Surely there is either sufficient clearance or there is not?

Regards,

IanT
The side cutting edge is an intersection between two planes, the relief angle and the side rake angle. This forms an included angle defined by those two planes, right? You can reduce the included angle by increasing either the rake or relief angles and the result would be the same; I assume this is what you mean by "sharpness". The downside to increasing the relief angles is that you lose some support under the cutting edge so tool life tends to go down but a little bit goes a long way.

But here's the thing. I used to think that once you have clearance then you have it. That was until I measured motor load and varied the relief angles and found a reduction in motor load as the relief angles increased. This can be due to a reduction in cutting forces (can't tell without a strain gauge) or that there is more rubbing than the published angles would lead us to believe or both. Regardless of which it is, a small increase in relief angle does reduce motor load and, by inference, cutting forces.

Hope that helps.
 

mikey

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Wanted to post a follow up on the ceramic belts that ate my keystock. They are excellent for grinding HSS and cobalt HSS. I used a 35 grit ceramic belt that shaped a tool about twice as fast as an Aluminum Oxide 24 grit belt. It also cuts much cooler. Normally, an AO belt turns the HSS a straw color due to the heat but the ceramic belt cut it faster and with no color change to the steel. The ceramic is a finer grit so I expected it to grind with finer grind marks but it is much finer than I thought it would be.

The 80 grit ceramic belt cuts much faster than its AO counterpart but cooler and faster, too.

Bottom line - I found a new kind of belt. Bye bye, AO! Amazon carries them for a good price.
 

Fallriverbryan

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Wanted to post a follow up on the ceramic belts that ate my keystock. They are excellent for grinding HSS and cobalt HSS. I used a 35 grit ceramic belt that shaped a tool about twice as fast as an Aluminum Oxide 24 grit belt. It also cuts much cooler. Normally, an AO belt turns the HSS a straw color due to the heat but the ceramic belt cut it faster and with no color change to the steel. The ceramic is a finer grit so I expected it to grind with finer grind marks but it is much finer than I thought it would be.

The 80 grit ceramic belt cuts much faster than its AO counterpart but cooler and faster, too.

Bottom line - I found a new kind of belt. Bye bye, AO! Amazon carries them for a good price.
Hey Mikey
I have a medium coarse diamond wheel for sharpening carbide. Have you even used one to sharpen HSS? I've heard it is not advisable but I have done it while applying coolant during the sharpening process.

Sent from my SM-G950U using Tapatalk
 

mikey

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Hey Mikey
I have a medium coarse diamond wheel for sharpening carbide. Have you even used one to sharpen HSS? I've heard it is not advisable but I have done it while applying coolant during the sharpening process.

Sent from my SM-G950U using Tapatalk
No, I don't have any experience with that kind of wheel. I do have an Accu-finish that turns at 300 rpm and at that speed, finish grinding HSS is no problem. Using diamonds for steel is only an issue at high speeds; my limited understanding is that the heat can weaken the bonding agent that holds the diamonds on. I guess using coolant like you're doing would keep the heat down nicely, Bryan, so I'm not surprised it works.
 

mikey

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I forgot to mention that these ceramic belts seem to last longer than the AO belts. I ground 9 model tools, a HSS tool and two Rex AAA (5% cobalt) and the belt seems to be as sharp after all of that as it was in the beginning. It took me just a few seconds longer to grind each face of a cobalt tool than it did to grind them on mild steel keystock.

I am really impressed with these belts!
 

ttabbal

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3dp examples came out good, they aren't 100% accurate but the labels turned out readable and give a good idea of what the finished product should look like

well they would be at least if I didnt print them in black, hah.

That's great! I have a 3D printer and would be willing to print some up for group members when the models are ready.

Been on vacation and catching up with the thread. Great stuff mikey! Thanks! Now I need to come up with something to grind them with.
 

DHarris

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OK all, I just received Mikey's model tool in the mail (Monday @ 12:00 noon Calif. time). Started to run right out to the garage when wife grabbed me by the ear and said "eat lunch first because I know I won't see you till after dinner time". So, dutifully obeying - I choked down lunch and THEN ran out to the garage!

Note - I'm a complete newbie on lathe tool grinding!

First thing I did was to cut and pasted all of Mikey's write-ups into one single MS Word document (all 23 pages of write ups! Hell of a task and job well done by Mikey, I might add!). Printed it out and into the garage I went. Started with the basic RH cutting tool. Followed the instructions step - by - step and compared my tool to the Sample Tool. It was amazing, even on my old rickety belt sander it took less than 20 minutes to grind. And, this is with me going from 36 grit, to polish with 80, and then just for S%its & Giggle's 220 grit. finished off with honing it. IT CAME OUT GREAT!!!!! and the bloody thing is SHARP!

Apparently, for me at least, what has been missing was a simple step - by - step walk thru to make it clear and easy to do!

Other things i discovered while grinding the 3 sample tools - -
1) the platen on my belt grinder is not rigid enough.
2) Belt grinder motor is a wimp - it's 30 years old & from harbor freight
3) Table is definitely not rigid enough - flexes down from left to right under pressure (is
only held on left side by one bolt.
4) No easy, accurate & repeatable way to place angles on table

So, basically, belt sander is crap - - good for general roughing & / or wood sanding in garage. OH BOY, VALID EXCUSE TO BUY A NEW TOOL!!

Attached is a photo of the tool model (bright shiny tool on right) and my grind (dull color on left). Note: I had not put the slight rounding of the nose on my tool when this photo was taken.

IMG_20170925_135356400.jpg

A final note - - after grinding the 3 samples tools in key stock - I duplicated this RH tool in a cheap Chicom metal HSS tool blank I had laying around. Put it in the tool holder in my Sherline lathe & started making cuts I never would have thought possible on this small lathe.

THANK YOU MIKEY FOR TAKING THE TIME & PUTTING IN THE EFFORT TO HELP US NEWBIE'S LEARN & GROW IN THIS HOBBY! (and yes, I did blame you for needing the new belt sander when I told the wife!)

Dave Harris

ps, It's now 2:30 Calif. time & I'm prepping the 3 sample tools to send up to Canada tomorrow! So, in roughly 2 hours I cut the 3 sample tools, one HSS tool and made some cuts!
 
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