Jon wrote:

Please help!

I need to know how to make 8 threads per inch on a tos trencin type sv18ra.
Nobody in the shop can figure it out. I have looked all over for reference
material that would help, with no luck. Any help would be greatly
appreciated.



Does it have a metric or imperial leadscrew? Most imperial leadscrews on
larger lathes are 8 TPI, so all you need is a 1:1 ratio between the
spindle and
the leadscrew. That should be easy to accomplish.

If the leadscrew is metric, only, then it gets more difficult. Some
lathes have
transposing gear sets that can be inserted in the gear train to make an
approximate
conversion between metric and imperial threads. But, because it is an
approximation, and the basic leadscrew thread is the wrong pitch, you
have to back up the lathe to wind the carriage back to the starting point.
You cannot disengage the half nuts until you are done with the thread.

Jon