A boring table for a Craftsman 12" lathe

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vtsteam:

I checked the threading tool against the compound slide's acme thread and the fit was really good. No play at all and the end of the cutter bottomed out perfectly in the thread. So the profile wasn't the problem.

I had a feeling that the thread wasn't deep enough -- even though I thought I was cutting to .520", maybe I wasn't

I decided to try one more scrap piece of aluminum, and this time not only cut a register in it, but also blued it so I could see for sure when the cutter touched the outer bore. This one took a lot longer to thread -- which was a hint that the others were indeed too shallow.

When it was done I also measured the inner bore -- I had bored .420, but when measured after threading, it was .410. I think the aluminum burred outwards -- I used a round file to bring it back to .420.

When I tried it, the scrap piece threaded on the acme screw -- finally! Well, most of the way. I think the thread was still a little shallow at one end. So I realized I probably needed to make a few more spring passes to clean up the end of the thread. Small holes like these necessitate slender boring tools, with a fair amount of spring. The fit was quite good otherwise -- no apparent backlash when wiggled. So I think I have the problems all figured out.

This would all be a lot easier if I'd had a piece of left hand acme rod to test the piece as I threaded it. I could just thread until I had a good fit, rather than watching a register. With the register method, you only have one shot to get it right, because you have to remove the nut from the chuck to try it on the lead screw. It can't be threaded any deeper on the lathe after that.

Anyway glad to have some answers to the problems.

vtsteam:
Before starting this morning, I thought I'd give myself some extra insurance by calculating what the compound slide should read when the thread is fully cut. Well, in an ideal world anyway.

Because I'm cutting this thread using the compound set at 14.5 degrees, rather than the straight in method, each division on the compound does not equal the actual distance cut straight in.

To calculate the difference, I figured it would be the inverse of the cosine of 14.5 degrees times the tooth depth I want to cut.

The inverse cosine of 14.5 degrees is 1.033 and the tooth depth is .05" so 1.033 x .05 = .0516". Round that to the nearest thousandth and it's .052" So as a check on the depth of cut, I should be turning the compound slide in a total of .052" on its scale. If I've done that, and I'm also starting to cut my register on the part, I should be at full depth of cut.

Fingers crossed!

vtsteam:

Finally!

It took one messed up hole when I got out of sync threading, but there was enough stock to make two. I'll cut the mistake end -- the square one -- off and fit the other to the boring table.

Man that was a lot of work for one nut! :Doh: Well at least I learned a lot.... :coffee:

I may try again to make a tap, as long as I have the lathe set up for threading.

awemawson:
Well done Steve. It all came right in the end due to doggedness on your part.

dsquire:
Steve

I knew that you were going to stick with it until you had it dancing your tune. Fine job. :D :D

Cheers :beer:

Don

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