Gallery, Projects and General > How to's
How to make a internal/external threading tool on your lathe
fatal-exception:
--- Quote from: AdeV on August 25, 2010, 04:21:42 AM ---Does it matter how far over-center you go when doing the milling operation?
--- End quote ---
Yes, but only really for how much clearance angle there is VS how much meat is left at the cutting edge. The drawing shows how much to mill off. (I've posted the link in the original post)
As far as tempering, yes, if you feel so inclined you can polish the top then gently heat it up till the polished area is anywhere between straw yellow and light blue. Straw yellow will yield the hardest temper with the least ductility, light blue will be the softest but the toughest. If you are going to be threading on an interrupted bar, then go for tough. Personally, I leave the tool full hard as I never take interrupted cuts while threading. Also, the hardness gradient is very short, going from glass hard at the cutting edge to full soft somewhere along the shoulder. Keeping it full hard keeps a keen edge for a long time.
Thanks for the comments.
Paul
andreas:
Brilliant idea!!!! Well done Paul!! :headbang: :headbang: :headbang:
crabsign69:
that was a great write up i put it in pdf if its ok with you :beer: :mmr:
thanks for the write up and all that very good
Dean W:
Nice write up, Paul! I do have a question and comment.
For brass and aluminum, leaving this dead hard is probably just fine. I think for threading steel, folks
would be happier if they temper it, as it will be less prone to cracking in the harder metals.
I wonder if the top cutting surface should be more on center. I mean, mill away less from the finished
end of the cutter, so it ends up closer to centerline on the lathe. Obviously, if a guy is cutting internal
threads, the "round" part on the end has to fit the hole, so as long as the end of the cutter is a radius
less than the part you are threading, you should have bottom clearance.
It would leave the shaft part of the cutter that is directly behind the sharp edge a bit larger in diameter,
making it stronger.
I think it's a dandy tool, and next time I need to grind a HSS bit for small inside threads, I'll try this instead!
Oh, by the way, old dog food tins make better quench cans than the ever popular pistachio can. The tools
come out better, and you don't get the munchies while toolmaking. This comes from many years of experience
and testing quench cans while making my own tools. Wash the can first, or you'll have dogs sniffing around the
shop from the smell of 'boiling dog food soup' ; )
Thanks again for the how-to. Great job on the pics and text.
Dean
andyf:
--- Quote from: Dean W on August 25, 2010, 06:14:37 PM ---Nice write up, Paul! I do have a question and comment.
For brass and aluminum, leaving this dead hard is probably just fine. I think for threading steel, folks
would be happier if they temper it, as it will be less prone to cracking in the harder metals.
I wonder if the top cutting surface should be more on center. I mean, mill away less from the finished
end of the cutter, so it ends up closer to centerline on the lathe. Obviously, if a guy is cutting internal
threads, the "round" part on the end has to fit the hole, so as long as the end of the cutter is a radius
less than the part you are threading, you should have bottom clearance.
It would leave the shaft part of the cutter that is directly behind the sharp edge a bit larger in diameter,
making it stronger.
--- End quote ---
Dean, though I agree with you about tempering to make it less brittle, I reckon Paul got it right by milling down to its centre-line. Anything above or below would reduce the tip angle, when viewed from above, to something less than 60o.
This could be compensated by a more obtuse angle, but the :smart: would be beyond me. I suppose too much resharpening by stoning down the flat top would eventually reduce the angle by an unacceptable amount.
Like Paul said, a purist might argue that such a tool would have zero relief for a tiny distance under the tip when used on the lathe's centre-line. But it works for him, so there's no reason why the copy I'm going to make shouldn't work for me.
The method could be adapted to make boring bars, too, where angles aren't so critical.
Andy
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