SJ wrote:

Hi and thanks for all your responses to my question yesterday about how to
cut a 4-start thread on a small lathe. I'm going to try the dog approach
since it seems the easiest to set up and probably gives good results.

My second question is about the other half of the equation: the nut that the
4-start 1/4"-20 screw uses needs to obviously have the same threaded type to
work properly. The nut is about 1/2" thick. Because the hole is small (for a
1/4"-20 thread), other than having a custom 4-start tap made (expensive?),
are there any tricks to cut this 1/2" long 4-start 1/4"-20 internal thread?
I know that my current internal threading tool for the lathe can't do a hole
this small.

Thanks again,
Sam




I have never tried it but I would try a tap standard 1/4 20 and grind
off all but one row of threads for clearance. Leave four full teeth on
the existing row and grind the rest off. Run the feed at 5 tpi. You
may need more relief because of the greater lead so you may have to
grind off the back side of the four teeth left to get the added
clearance needed.


John