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Your hands, and fingers are getting used to the orientation needed, which makes your confidence go up too. I am still not 100% comfortable with the lapping plates, and the flatness needed for a good hone. Good job. 
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Models for grinding HSS Lathe Tools
- Thread starter mikey
- Start date
It's funny. I'm actually MORE likely to grind facets into the tools with the belt grinder than the diamond plates. Just goes to show that everyone is different. 
Nice to see more people being successful grinding tools. It's a very useful skill even if you use a lot of inserts.
Nice to see more people being successful grinding tools. It's a very useful skill even if you use a lot of inserts.
- Joined
- Dec 18, 2019
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Yesterday I ground a LH knife tool. It's not pretty by any means. I had a lot of trouble putting in the top face due to the limitations of my belt grinder. I really find it hard to do the honing. First it's the patience to go through all the grits. Definitely getting better at that. Fine grit will not remove gouges, only the coarser (coarsest) will do that. So get it flat with the coarsest grit possible! If that is done, going through the grits is easy. Don't use a lot of pressure, let the grit do the work. Just work on the mechanical movement of your hand to make it as robotically smooth as possible. That helps immensely. If you can only take 1 inch strokes but they are flat, you will eventually get there.
The tool did the job that I needed it to do. I had to remove 0.004" from the bottom of the head of a shoulder washer. There's a lot of freedom when one can grind one's one lathe tools..
Bushing (shoulder washer) is under the leftmost screw. I had to remove 0.004" from the bottom side of the flange, which made the distance between the plates 0.004" wider. This prevents the center arm from binding on the outer plates.
The tool did the job that I needed it to do. I had to remove 0.004" from the bottom of the head of a shoulder washer. There's a lot of freedom when one can grind one's one lathe tools..
Bushing (shoulder washer) is under the leftmost screw. I had to remove 0.004" from the bottom side of the flange, which made the distance between the plates 0.004" wider. This prevents the center arm from binding on the outer plates.
I was reading through this tome again a week or so ago, and came across a comment of Mikey's that he would make a roughing square with fewer compromises than an all purpose square tool, with 15 deg SRA, 12 deg ERA, 24 deg side rake and 15 deg back rake. So I tried one... actually forgot to change the table from 15 to 12 for the end cut so both are 15. That 24 degree side rake was a bear to grind, and it's cobalt!
But it cut really well. The final picture shows a .020 cut @780 rpm and .004 feed, the thicker portion on the left, polished a little with emery. I need to make the nose radius a bit more even. Also, it's not flat since I'm using a 6" bench grinder, not a belt.
Thanks for looking!
Tim
But it cut really well. The final picture shows a .020 cut @780 rpm and .004 feed, the thicker portion on the left, polished a little with emery. I need to make the nose radius a bit more even. Also, it's not flat since I'm using a 6" bench grinder, not a belt.
Thanks for looking!
Tim
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About a week ago, I finally finished a square tool in cobalt steel. I must be doing something wrong as the tool lasted maybe 5-10 minutes before the tip breaking. I had made a flat on the edge and attempted to radius it. This isn't the first time I've "accomplished" this. It's getting frustrating putting in so much work honing only to have the tip break off. All 4 of my square tools, be they HSS or cobalt have done this. Clearly something isn't right.
So, perhaps only for my review, how should the tool be used? Wrong angle with respect to the workpiece? Asking myself if it's tool abuse, junk metal, or bad grinds or what? My carbide tips TCGT don't last as long as I'd like either. They are delicate and I tend to chip them, even when it's not an interrupted cut. I store the tools in their OXA holders in red plastic Schaller bins. I'm not purposely jostling them together. If there's two in a bin I face them so the dovetails overlap and the points are far from each other.
I'll get pictures when I get back to the shop.
So, perhaps only for my review, how should the tool be used? Wrong angle with respect to the workpiece? Asking myself if it's tool abuse, junk metal, or bad grinds or what? My carbide tips TCGT don't last as long as I'd like either. They are delicate and I tend to chip them, even when it's not an interrupted cut. I store the tools in their OXA holders in red plastic Schaller bins. I'm not purposely jostling them together. If there's two in a bin I face them so the dovetails overlap and the points are far from each other.
I'll get pictures when I get back to the shop.
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Mostly easy stuff, 12L14, 6061. I have done O-1, but not much. It's all manual right now, slow feeds. No tach, but relatively low speeds based on the rheostat. But maybe the SFM is off. I need to be more careful about that. You guessed right. Mini-lathe.
If I set it up to feed, it's too fast, due to how the mini-lathes are geared. So I get a better finish with a manual feed. (Backwards, right?) One day I'll make a bigger gear to reduce the feed rate. The breakages have been primarily on steel.
Odd that the feed is so far off. I would think they would include a gear that could get you down to 0.005"/rev or less. That's what I usually do for roughing.
Nothing against mini lathes, beats no lathe. just helps to have an idea of ridigity available. What depth are you trying to cut?
No tach... You should consider adding one or even just a standalone tach gun. They are inexpensive and help a lot. If you are wearing carbide tips quickly, it makes me think that you are running faster than you might expect. And if the speed is enough to wear carbide, it's likely to burn HSS pretty quickly. For now, if your machine has belts to adjust speed ranges, make sure you are in low range. Then turn it down and use a smallish diameter workpiece. Perhaps 1" or less aluminum. Just to get a feel for what's happening. Take a pass and look at the finish, chips, and heat levels of the material and the tool. Those can tell you a lot about the forces on the tool. On steel, do you have the chips changing color?
Can you post a pic of the tool angles you have?
Nothing against mini lathes, beats no lathe.
just helps to have an idea of ridigity available. What depth are you trying to cut? No tach... You should consider adding one or even just a standalone tach gun. They are inexpensive and help a lot. If you are wearing carbide tips quickly, it makes me think that you are running faster than you might expect. And if the speed is enough to wear carbide, it's likely to burn HSS pretty quickly. For now, if your machine has belts to adjust speed ranges, make sure you are in low range. Then turn it down and use a smallish diameter workpiece. Perhaps 1" or less aluminum. Just to get a feel for what's happening. Take a pass and look at the finish, chips, and heat levels of the material and the tool. Those can tell you a lot about the forces on the tool. On steel, do you have the chips changing color?
Can you post a pic of the tool angles you have?
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Max RPM is 2300 on my mini-lathe. I don't run it that fast cutting! Mini-lathe just isn't rigid enough for that. The speed is electronically controlled, there are no belt positions to shift. I'm usually running near 650 RPM, but that all depends on lots of stuff, like diameter, and if there's chatter. If there's chatter then I back off. Got to confess, I tend to forget running the SFM calculation, but it's rare that I'm machining poor machining steel. There's allegedly a tach output connector on the lathe, but the display was wildly overpriced a year ago. Maybe I can make an Arduino read out the pulses and display it for a lot less.
DOC's are very modest only 0.010 to 0.015. I let the lathe tell me what it can do, so I don't push it beyond what it can do. This makes lathework kind of slow, but, that's what one gets with that entry price point. Gibs are adjusted to be relatively tight to minimize lifting and to maximize rigidity for the platform.
I seem not to be wearing carbide, it's more chipping. It could be a function of the quality of the inserts and the type. But this thread is about grinding tooling, so let's focus on that. More specifically the square tool. I haven't had an issue with my knife tools, left or right hand. Maybe that's because I only use them to shave off a thousandth or two. I have yet to crack the tip on the knife.
What do you mean by tool angles? The grinds themselves or the angle of the tool when on the lathe?
Here is a square tool that is in process, it's not completely finished. It's in HSS. I have not put a flat on the edge, nor radiused the edge. Honing is not complete, especially the small flat in the third picture.. The shape is representative of my other square tools. I will bring up the chipped cobalt one and photograph it as well. In my mind, thought the cobalt one came out better, but the photos will be the judge of that.
DOC's are very modest only 0.010 to 0.015. I let the lathe tell me what it can do, so I don't push it beyond what it can do. This makes lathework kind of slow, but, that's what one gets with that entry price point. Gibs are adjusted to be relatively tight to minimize lifting and to maximize rigidity for the platform.
I seem not to be wearing carbide, it's more chipping. It could be a function of the quality of the inserts and the type. But this thread is about grinding tooling, so let's focus on that. More specifically the square tool. I haven't had an issue with my knife tools, left or right hand. Maybe that's because I only use them to shave off a thousandth or two. I have yet to crack the tip on the knife.
What do you mean by tool angles? The grinds themselves or the angle of the tool when on the lathe?
Here is a square tool that is in process, it's not completely finished. It's in HSS. I have not put a flat on the edge, nor radiused the edge. Honing is not complete, especially the small flat in the third picture.. The shape is representative of my other square tools. I will bring up the chipped cobalt one and photograph it as well. In my mind, thought the cobalt one came out better, but the photos will be the judge of that.
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If your mini-lathe is similar to mine, the feed rate is 1/256 of the spindle speed. That is about 0.004"/rev. This is calculated as (20/80) * (20/80) * (1/16) = 1/256. The 20/80 reduction is from the gear train and the 1/16 is from the lead screw pitch. Beware that this is for my Micro-Mark Tru-Inch mini-lathe, yours might be slightly different. But, you can do the same calculation.
I converted to Clough42's ELS system. Now, I can dial in 0.001"/rev up to 0.040"/rev. The ELS gives you RPMs as well. You might want to consider doing this conversion as you can change the feed rate as you are turning. This makes it easy to turn to a shoulder by slowing the feed rate as the cut nears the end. Also, you get metric threading for free!
I'm still learning to grind my HSS lathe bits. I found the belt grinder orders of magnitude easier than a bench grinder. It's vastly faster and cooler and you get flat faces. My turning improved a lot by getting and keeping the faces polished by honing. It's makes a big difference. I can take take 0.040" DOC in steel now. Before I was taking between 0.005" and 0.010" DOC.
I converted to Clough42's ELS system. Now, I can dial in 0.001"/rev up to 0.040"/rev. The ELS gives you RPMs as well. You might want to consider doing this conversion as you can change the feed rate as you are turning. This makes it easy to turn to a shoulder by slowing the feed rate as the cut nears the end. Also, you get metric threading for free!
I'm still learning to grind my HSS lathe bits. I found the belt grinder orders of magnitude easier than a bench grinder. It's vastly faster and cooler and you get flat faces. My turning improved a lot by getting and keeping the faces polished by honing. It's makes a big difference. I can take take 0.040" DOC in steel now. Before I was taking between 0.005" and 0.010" DOC.