A boring table for a Craftsman 12" lathe

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vtsteam:
I also milled off some of the excess at the back side of the cutter:

vtsteam:
After milling. There is still too much material on the end. Additional relief needs to me removed under the cutting edges because the relief angle is too shallow.

vtsteam:
I blued the cutter edge and gradually filed it away, watching the blue mark:

vtsteam:
When I got close to no more blue, I switched to a bench stone and took the last of it off. Then it was time to harden the cutter. This went without a hitch with REAL drill rod, and a file couldn't scratch it. I left it full hard, as none of my earlier trials yielded a broken cutter -- screw cutting happens at slow speed with light cuts and they aren't interrupted. Maintaining the keenest possible edge is important, so that was my choice.

I left cutting edges at both sides of the tool for the time being, since I though I'd try cutting a tap with the outside facing lip. After that I planned to grind it off so the cutter could fit the bore when internal threading.

Cutting a tap proved impractical with this tool. The boring tool holder was in the way of either the chuck or the tailstock since this is a tool designed to be aligned parallel with the bed. 1/2" tap stock had too long an overhang to be solid enough on my lathe without support by the tail center.

Low speed chatter was the result when trying to thread drill rod. It left a horrible finish. Much better would be a conventional lathe tool, ground to do a 29 degree thread. You would have a shorter tool extension, plus support by lathe centers. So after fooling around for an hour or so I finally gave up and ground off the extra lip.

I did a practice piece in both aluminum and brass, left hand internal threads, and finally chucked up in the 4 jaw the stock I intend to use for the actual leadscrew nut. A old scrap block of either brass or bronze, I'm not sure yet what it is. I'm thinking bronze -- need to clean it up more to see the true color. It's acting like bronze -- maybe even aluminum bronze as it was quite tough to drill.

I figure I've got two chances with this block -- the hole I drilled is near one end. If I screw up screwing, I could try again at the other end -- it's long enough to cut off the mistake and try again.

By the time I had the first hole drilled it was supper time -- time flies. I'll have to bore to ,420" tomorrow, and then cross fingers it'll thread right this time.....

The cutter after hardening:

Ready for tomorrow:

vtsteam:
The day's about half over and I still haven't cut that nut. A bit frustrated. I tried one more test piece -- seemed perfectly cut, no mistakes, put a bore on the end to tell when cut to proper depth, reverse thread 14-1/2" degree grind, new cutter, etc. But it wouldn't screw onto the cross slide lead screw.

I decided I wanted to measure that screw, but it's well buried in the cross ways. I tried removing it but it's trapped by the the drive gears, and to fully remove It I'd have to loosen what appears to be a 1-5/16" hex on the support spigot. I don't have a wrench that size.

Then an Idea! What about the compound slide screw -- could that also be a 1/2" 10 TPI acme? Yes indeed! And I can get it out much more easily. Finally I have it, and measure the OD which is a thou under 0.5" -- that's okay. And the thread depth which was about 0.407" also good. I was cutting the thread to .420 and .520.

So I tried the nut. Weird-- it cocked sideways and wouldn't screw on. Eventually dawned on me that the compound slide has a right hand thread, and the nut was left hand to suit the cross slide :doh:

So the lathe has a left hand thread on the cross slide and a right hand screw on the compound slide. No wonder I sometimes get mixed up turning dials. Well, then, I thought, you did make a right hand nut by mistake yesterday, try that on the compound screw.

But no, something is wrong, and so far I'm not sure what. But finally I have a sample of the acme thread that I can check the cutter profile against. I can also use it to make a conventional lathe tool in case I finally have to resort to making a tap.

Man what a time waster this has been! :bang:

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