Lathe keeps cutting away threads. All appears fine, but wont thread. Been working with distributor tech support for over a month to resolve. No help. Lathe is tight and in good shape. Will not thread even if you leave half-nut engaged and use lead screw left-right transmission. But it appears to hold true if I leave lead screw trans engaged AND half-nut engaged and use on Motor fwd/rev. Cant thread that way, but it is information. Also discovered this am that my thread dial that has 6 number marks onlyand no half marks, checks out showing each number mark moves the carriage .551 per mark?? Lead screw itself and gear inspect as clean and proper. Half-nut looks ok as well. Anybody have any ideas?
Thanks,
KCL
NEW INFO!
On viewing another post, I found an individual who describes my exact issue. He stated the problem is in the fact that his thread dial is 6 position marks as is mine and has 17 teeth, as is mine. Apparently some threads have to be calculated to allow many full rotations of the lead screw before re-engagement to cut some threads.
Quote:
Hi,
I finally figured out why cutting 8 TPI on the Craftex CT089 lathe was not working. Specifically, closing the half nut using the suggested thread dial indicator reading of "2" kept overcutting the previous thread. I finally decided to explore the math of the problem and here is what I found:
For 8 TPI, the chuck rotates 8 times while the carriage advances 1.000 inches. The leadscrew is 5 TPI so one turn of the chuck turns the leadscrew 5/8 turn and advances the carriage 1/8 inch. The thread dial indicator has 17 teeth and 6 marks, so 17 turns of the leadscrew will turn the TDI one revolution and advance the carriage 3.4 inches which would cut 27.2 threads. This is the problem; it is not possible to use this TDI to measure 8 TPI because there is no integer number of threads from one revolution of the TDI. There would need to be five turns of the TDI to get an integer number of threads, i.e. 5x17 turns of the leadscrew which is 17 inches of carriage movement or 136 threads.
Putting this to practice, it worked! It's a bit of a wait for the TDI to rotate five times before engaging the half nut, but it did work.
Ideally, I'd like to change the TDI gear to 20 teeth then the half nut could be engaged on the whole turn of half marks. Not sure why 17 teeth was chosen for the TDI gear.
Hope this helps!
Cheers,
Thanks,
KCL
NEW INFO!
On viewing another post, I found an individual who describes my exact issue. He stated the problem is in the fact that his thread dial is 6 position marks as is mine and has 17 teeth, as is mine. Apparently some threads have to be calculated to allow many full rotations of the lead screw before re-engagement to cut some threads.
Quote:
Hi,
I finally figured out why cutting 8 TPI on the Craftex CT089 lathe was not working. Specifically, closing the half nut using the suggested thread dial indicator reading of "2" kept overcutting the previous thread. I finally decided to explore the math of the problem and here is what I found:
For 8 TPI, the chuck rotates 8 times while the carriage advances 1.000 inches. The leadscrew is 5 TPI so one turn of the chuck turns the leadscrew 5/8 turn and advances the carriage 1/8 inch. The thread dial indicator has 17 teeth and 6 marks, so 17 turns of the leadscrew will turn the TDI one revolution and advance the carriage 3.4 inches which would cut 27.2 threads. This is the problem; it is not possible to use this TDI to measure 8 TPI because there is no integer number of threads from one revolution of the TDI. There would need to be five turns of the TDI to get an integer number of threads, i.e. 5x17 turns of the leadscrew which is 17 inches of carriage movement or 136 threads.
Putting this to practice, it worked! It's a bit of a wait for the TDI to rotate five times before engaging the half nut, but it did work.
Ideally, I'd like to change the TDI gear to 20 teeth then the half nut could be engaged on the whole turn of half marks. Not sure why 17 teeth was chosen for the TDI gear.
Hope this helps!
Cheers,
Last edited:
