Lathe Machine Query

To cut parallel threads on a lathe, the lead screw only needs to be advanced in synchronism with the rotation of the workpiece. Advance of the feed screw would only be required for cutting a tapered thread.

https://www.rg-group.com/resources/blog/whats-the-difference-between-parallel-vs-tapered-threads#:~:text=Tapered%20threads%20utilize%20a%20metal,increasingly%20interfering%20with%20mating%20threads.

A lathe cuts threads. When the half nut is engaged to the lead screw, it cuts a very coarse thread, something like 4 - 80 threads per inch or so.

When the half nut is disengaged, it cuts a much finer thread, hundreds of threads per inch. The finished piece looks and feels relatively smooth, but it's actually a thread. If a large radius cutting tip is used, the resulting surface is even smoother.

Hope this is what you're looking for.

Unless You have a jewelers lathe 4-80 is considered a fine thread. To single point a thread any smaller would require a very small tool and a precision lathe.

oilcan13

Simply yes.

On the less expensive lathes, it is common practice for the lead screw to provide power for both feeding and screw cutting. In those examples feed power is provided by the keyway on the lead screw, not the screw threads. It is a either/or choice made within the apron by a select lever.

Back in the dark ages I learnt to use the lathes at TAFE and in the workshop of the employer and they were old British lathes driven by a flat belt.

To cut a thread the the correct gearing was chosen from a lookup table having regard to the number of threads per inch on the leadscrew. We were taught to set the top slide over so that the tool advanced on an angle so the front face always did the cutting.

If the tool was kept parallel to the workpiece then the cut is across the whole of the tool front and added more load as the cut became deeper. Small threads were not a problem but start cutting deep threads with less TPI and the load can become very large. Threads on a lathe are cut by the rotation of the leadscrew.

Taper threads can be achieved by disconnecting the cross slide screw and attaching a taper turning attachment to the rear of the cross slide and turning the taper first before threading.

The second method

All lathes I have seen have no option to use power feed and thread cutting simultaneously. It's either power feed or thread cutting, but not both. The gearing mechanism in the saddle of the lathe is built to prevent simultaneous engagement.

For tapered threads you would need to have a taper attachment as shown in one of the other posts.