Turning

Subject:
Re: thread cutting with jigs
Response To:
thread cutting with jigs ()

John K Jordan
That's good information, thanks!

I noticed issues from the wood moving on my first try. Remembering what Raffan said about making boxes, on the second one I shaped the outside then the inside (where the threads would be) most of the way then let it sit overnight. This evidently allows any residual moisture that was inside the blank to escape through the thin walls. It also allows stresses to relax. Then I turned it round again the next day.

More than once once on "normal" boxes I noticed that the perfect turning from the day before had gone out of round overnight. On the second threaded box I made it round again on the inside and lightly sanded with 600 to smooth the transition. The thread cutter scratched all the way around on this one.

I wonder if relaxing the piece overnight might be a good reason to turn and thread the bottom, or larger section first before the smaller lid. I also partially hollowed the lid and let it rest but there was not nearly as much wood and it didn't move as much. (Maybe also because it was Gaboon Ebony.) Having enough chucks to keep each part chucked until finished is a big plus. The hard part was test fitting with both pieces still in the chuck.

BTW, at one place after making the .020 cut you mentioned that you might take of just another .050" and sneak up on the fit - I assume this should have been .005 instead of .050.

As for aligning the jig: The Baxter jig fits pretty well into the gap in the ways but there is a tiny bit of play. I didn't think of it until you mentioned it but I could easily machine a metal stop to fasten to the ways in front of the jig. Maybe hold it with magnetic clamps. Then I could slide the jig away from the cutter to more easily do a test fit then register it exactly into place for another cut.

I bought the jig to fit the Jet 1642. It sure is nice to have the second lathe set up! I turn the pieces on the PM and kept the jig set up on the Jet.

I have tried threading wood with a tap before and it was awful! The threads worked but looked horribly chipped and broken. I too don't like the flats on the top of the threads but they sure beat chips. I have three different books that discuss threading with a jig and all of them mention the flats can prevent chipping on some coarser or softer species.

Do you have guidelines for the height of the threaded tenon and the number of threads to shoot for? Do you tend to use the same number of threads on everything?

Oh, one more question - when you did the threaded box ornaments did you jam chuck 1/2 to turn the finials? I thought about turning a throw-away "threaded chuck" from scrap wood to screw on half to hold it for finish turning. Do you see any problems with this other than it being extra work? (I finish turned the lids this way, screwed on to the base still in the chuck.)

Thanks for writing this. When I get time, probably not until Saturday, I want to try a larger box about 2.5" diameter, also from B&W Ebony. I may have more questions!

JKJ

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