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Cutting threads with no index plate


Active Member
Found a mention of cutting threads on gear change lathes when indexing plate is missing/unreadable. This applys to inch lead screws.
Multiply number of threads per inch on lead screw and the number of threads to be cut by a common number that will give a result for the gears with the lathe. Eg. want to cut 10 threads per inch, and have an 8 thread lead screw.
4x10threads to be cut = 40
4x8 thread of lead screw = 32
Gears to use, 40 and 32 tooth gears. If the thread to be cut is a finer thread then the lead screw, the smaller gear goes on the spindle stud, larger one on the lead screw. Other way if thread being cut is courser then lead screw.
If 40 tooth and or 32 are not in supply, multiply by another number, 5,6,7 or.
Check thread pitch with first light cut.
I don't remember this from school, but that was some sleeps ago. Not sure if commonly known or not. There maybe the same for metric, no idea. And I can't try it out as my geared lathe is in Saskabush country with a son.
Hope this may help someone.