Stepper motor problem

Author	Message
Godoh Guru Joined: 26/09/2020 Location: Australia Posts: 677	Posted: 01:00am 16 May 2026       I recently fitted an electronic lead screw to my lathe. It came as a kit from China and works well. I had to change the gearing on the stepper motor that drives the lead screw as the controller would not allow me to adjust it accurately enough. I fitted a couple of the old gears that were in the back of the lathe to give me a 1.2 reduction from the motor to the lead screw. Now I have it adjusted so I can cut threads on the lathe. I couldn't do that before because i was given the lathe years ago and my friend had lost the back gears, so as a lathe it was good, but thread cutting was out. Since fitting the gears to the stepper motor and to the lead screw, i have cut some fine threads and it is working well. But if I try to set the thread to say a 12 tpi thread, the stepper motor goes mad and doesn't seem to know what to do, it makes a terrible noise and stops itself after a short time. I am wondering if it is picking up some stray signal that upsets it, it cuts fine threads perfectly but goes into freakout mode on coarse ones. I don't have access to the controllers programming except to change settings for the lead screw movement, the pulses from the controller and how many pulses the unit measures from the encoder. I am hoping that someone here can tell me what to do, the stepper motor ran fine on coarse thread settings when it had a toothed belt drive to the lead screw, on a 1:1 ratio. But now it has a step down 1.2:1 ratio it doesn't like it. Thanks Pete