Models for grinding HSS Lathe Tools

tmenyc said:
Looks good!

Mikey,
I know you told me way back, but I can't find it, about what angles to use for acetyl and ebonite (also known as vulcanite, it's compressed organic hard rubber, still used for smoking pipes and saxophone/clarinet mouthpieces and, for me, replacing vintage fountain pen parts with original materials). I know you said that anything I use for aluminum would work, but now that I'm able to grind much more easily, I could make a tool and dedicate it to the softer stuff. What do you recommend?

Many thanks,
Tim
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Having zero experience turning this stuff, I don't know what would work best. This will be trial and error but I have a good idea of what would be needed. However, rather than just coming out with it, this might be a good exercise in designing a tool.

Vulcanite/Ebonite, from what I can find on the web, is a hard sulfurized rubber formed under high pressure with a softening temp of only about 160 deg F. That means that we have to keep the cutting temps really, really low. That suggests you need to turn this stuff at low speeds and somewhat higher feeds and that your tool MUST be optimized for lowering cutting temps. It must also be very sharp and you have to keep the tool moving when you turn the work to reduce temps. A stream of low pressure compressed air at the point of cut might also be helpful to keep temps low.

Rather than me telling you what I would do, why don't you guys tell me what YOU would do to meet the needs of the material? The shape of the tool can be a general purpose shape but what do you do with the relief and rake angles? More importantly, WHY are you choosing the angles you're choosing?
 
Mikey,
I love it ! And yes on the low pressure compressed air, have that already. I generally push around 20psi at the point of cut.
I guess I would want to maximize clearance to keep it cool and clear the work away, and to raise back rake. Maybe 20 deg side and end relief and 40 deg rake?

Tim
 
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Tim, our focus should be on lowering cutting temperatures; increasing side rake will do that most effectively. Increasing back rake will also lower cutting temps by accelerating chip flow and thinning the chip thickness. Leaving side and end relief at about 15 degrees will work fine. I would boost side rake to about 20 degrees and use a back rake of about 15-18 degrees. This amounts to an aggressive amount of rake and will definitely improve chip flow. Since most of the heat from the cut will go out with the chip, this should work well. I would keep the nose radius around 1/64".

Give it a try and remember to use your edges for finishing. The area just behind the nose radius on either the side or end will shear a really nice finish.
 
Interesting, so not based on the aluminum-use tool with severe back rake. I'll try it!
Many thanks.
Tim
 
I suggest you try this first and see how it works. If it cuts too hot then use more rake.
 
For a parting tool does any of the turning tool angles matter? I know you want to have a end cut angle so you can hopefully have a clean part on the back with no tit but is there anything else like the end relief?
 
I suggest a relief angle of 7 deg under the cutting edge. Hone the top flat.
 
Ok would a 2 degree end cutting angle be fine to get the **** cut off hopefully? Thickness be an 1/8" be ok most likely?
 
I would grind the end straight across. I've tried them all and a straight tip works best for me. The way to tell what works best for you is to try it and see.

I highly recommend you consider a P1-N or P1 blade. When rigidly held, they will cut almost anything your lathe could possibly hold. I use a P1-N almost exclusively on my Sherline lathe to cut up to 2" dia. work pieces. Keep in mind that parting tools are actually form tools; the wider the blade is, the higher the cutting forces will be. The key, of course, is to mount the blade in a rigid holder.

If you can rig it, mount it upside down and in the rear of the work piece. I can almost guarantee this configuration will make parting a breeze.
 
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