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.
The thread will come out exact, assuming the QC box has the right selection, since the metric way is thread pitch, while us imperial types do threads/unit of measure. But, you STILL have to back up without disengaging the half-nuts, because the leadscrew pitch doesn't repeat every inch.
Sorry, it is a lathe. Made in Slovakia, sometime in the '70s. I have access to the right cutter, I just wonder if it is possible to set this machine to cut 8 threads per inch without modifying it and if so how.