- Joined
- Nov 11, 2013
- Messages
- 7
I recently purchased a used PM1127VF lathe. The lathe came with 14 change gears for cutting threads. The manual lists the gear settings to do 21 inch threads and 8 metric threads. Wanting to learn more about threading and change gears I did some searching on the web. I came across this post by jimbojones132. http://www.hobby-machinist.com/threads/cx701-change-gears-oem-gear-list-and-additional-threading-options.40649/. Jim wrote a program to calculate the pitches for all the different gear combinations. Intrigued, I decided to write a program for the PM1127 and the gears I have.
The results were very interesting. Given my set of gears I can produce most any thread in many ways. For example there are 71 gear combinations which produce 14 TPI threads exactly. Plus there are another 119 gear combinations which get within 1%. Need 18.4 TPI? There are four gear combinations which are off by mere 0.049% and 233 others that are within 1%.
Now my question. Are some gear combinations better to use than others? Are there rules about what to do and not to do? For example never have a small gear drive a gear more than twice its size or always put a big gear on the lead screw. Or should I always put a small gear on the lead screw. That sort of stuff.
The book “Screwcutting in the Lathe” by Martin Cleeve hints that there are rules but never explains this fully (at least in the parts I have read). I was hoping people on this forum can help me out.
If my question is not clear, I can add more details.
Thanks for reading.
The results were very interesting. Given my set of gears I can produce most any thread in many ways. For example there are 71 gear combinations which produce 14 TPI threads exactly. Plus there are another 119 gear combinations which get within 1%. Need 18.4 TPI? There are four gear combinations which are off by mere 0.049% and 233 others that are within 1%.
Now my question. Are some gear combinations better to use than others? Are there rules about what to do and not to do? For example never have a small gear drive a gear more than twice its size or always put a big gear on the lead screw. Or should I always put a small gear on the lead screw. That sort of stuff.
The book “Screwcutting in the Lathe” by Martin Cleeve hints that there are rules but never explains this fully (at least in the parts I have read). I was hoping people on this forum can help me out.
If my question is not clear, I can add more details.
Thanks for reading.