Hi all,
I am rather new to this. I recently bought a Harbor Freight Sieg 7x12 and have done one small project on it. I would now like to do some threading, specifically for a hard-to-find watchmaking specific thread size (40tpi x .275).
I have read the Mini-lathe manual from Little Machine Shop, and some online documentation, but I am still a bit confused with threading procedures.
Here's how I have the cross slide and tool bit set up for threading. The tool bit is HSS.
And here are samples of a couple of threading attempts I made.
The bottom one is on aluminum, which came out OK, though still a bit rough. The top one is on annealed silver steel (I am attempting to make a tap) and it's just ugly (right end... don't worry about the left end). The threads end up very rough and subsequent passes at .005 still seem to strip off way too much metal.
I would have thought 40tpi would be an easy one to start with since the half-nuts can supposedly be engaged anywhere, but I am clearly doing at least something (if not everything) wrong.
FWIW, I went through today and adjusted the saddle thinking play there (which did exist and I did fix) might have been part of the problem. The attempts above, though, were after this adjustment. On a semi-related note, I noticed that there are two set screws visible from the top of the saddle (chuck end). The back one seems to be non-functional, as it goes into a blind hole. The front one I would have thought would adjust for front to back play on the saddle, but it doesn't really... I fixed this by making a brass plug with a 45 degree face to it and setting it under the front set screw. This allows me to put pressure on the 45 degree face of the ways and really cleans up the front/back lash of the saddle.
Any suggestions on the threading?
Thanks,
Paul