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New lathe is possessed
- Thread starter cannibal
- Start date
- Joined
- Jul 28, 2017
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- 2,574
The problem with your speed control issue probably is caused by a bad speed feedback loop, not a problem with the potentiometer. If you can find a schematic for your motor controller you might be able to troubleshoot the problem. Lacking a schematic you'd be looking at reverse-engineering the controller. If it uses a multi-layer board that can be really difficult. If Vevor is using a third party motor controller don't bother going to Vevor, go to the manufacturer of the controller.
Sometimes a manufacturing problem can be found by carefully inspecting the board. Look for cold solder joints, solder dross shorting component leads, and so on. PWM-style motor controllers use a current sensing resistor in the feedback loop so problems with the resistor, which typically is a higher wattage resistor, can cause problems. They can burn out, the connections become resistive because the resistor is running hot, and so on.
But in your case with a new lathe I'd concentrate on looking for manufacturing defects.
One diagnostic to check for a feedback loop problem is to see how the speed regulation works under load. Chuck something up and try making some cuts. If the motor significantly slows down the feedback loop isn't working.
Sometimes a manufacturing problem can be found by carefully inspecting the board. Look for cold solder joints, solder dross shorting component leads, and so on. PWM-style motor controllers use a current sensing resistor in the feedback loop so problems with the resistor, which typically is a higher wattage resistor, can cause problems. They can burn out, the connections become resistive because the resistor is running hot, and so on.
But in your case with a new lathe I'd concentrate on looking for manufacturing defects.
One diagnostic to check for a feedback loop problem is to see how the speed regulation works under load. Chuck something up and try making some cuts. If the motor significantly slows down the feedback loop isn't working.
I got an amazon 8x16 super generic. Its an e feedscrew. Same issues.
To solve them, so far.
The directional switch is wired before the on/off. I rewired it so power goes to the on/off, which has a relay built in so make sure it has power between line and N. I split the output of that to the directional switch and the e feedscrew, so the controller is active and can move. This will solve your idle problem. I use the directional switch to run the spindle only now
Next is the spindle speed.
My e leadscrew control has the rpm and degree count. The encoder from the spindle is a 3m belt with 75teeth on spindle and 20 on encoder. Thats a 3.5 to one ratio with the encoder saying its 1k pulse per rev. If you hold the controller function button, or something, it pulls a set up menu. I can adjust the encoder p/rev. It only goes to 3k. So no matter what, is not able to count rpm correctly. I ordered a 30 tooth, 6mm bore, 3m pitch pulley and new belt to correct this. I can then set my ppr correctly. The pulley hasn't arrived yet, but changing the ppr does move the rpm and degree as expected. Your rpm is messed up because the motor driver thinks it going faster than it is.
Also, for other other e leadscrew guys, the settings seems off. My tpi or more correctly mm, was off from the factory setting. The stepper output counter seems correct, adjusting the tpi can help dial in the actual carriage travel, vs a caliper. I have a 2mm screw but i set my controller to 1.95 or something.
The lathe seems pretty nice, its my first precision fab tool, im a jack of many trades. If you are willing to learn a little of basic electrical and basic encoder ideas, you should be fine.
To solve them, so far.
The directional switch is wired before the on/off. I rewired it so power goes to the on/off, which has a relay built in so make sure it has power between line and N. I split the output of that to the directional switch and the e feedscrew, so the controller is active and can move. This will solve your idle problem. I use the directional switch to run the spindle only now
Next is the spindle speed.
My e leadscrew control has the rpm and degree count. The encoder from the spindle is a 3m belt with 75teeth on spindle and 20 on encoder. Thats a 3.5 to one ratio with the encoder saying its 1k pulse per rev. If you hold the controller function button, or something, it pulls a set up menu. I can adjust the encoder p/rev. It only goes to 3k. So no matter what, is not able to count rpm correctly. I ordered a 30 tooth, 6mm bore, 3m pitch pulley and new belt to correct this. I can then set my ppr correctly. The pulley hasn't arrived yet, but changing the ppr does move the rpm and degree as expected. Your rpm is messed up because the motor driver thinks it going faster than it is.
Also, for other other e leadscrew guys, the settings seems off. My tpi or more correctly mm, was off from the factory setting. The stepper output counter seems correct, adjusting the tpi can help dial in the actual carriage travel, vs a caliper. I have a 2mm screw but i set my controller to 1.95 or something.
The lathe seems pretty nice, its my first precision fab tool, im a jack of many trades. If you are willing to learn a little of basic electrical and basic encoder ideas, you should be fine.
- Joined
- Apr 30, 2015
- Messages
- 12,313
Somebody give this man a cad program! 
- Joined
- Apr 30, 2015
- Messages
- 12,313
I just looked at the video in post #1 again and the motor control is clearly faulty- the spindle speed should not be rising and falling like that-
Completely unusable in that condition- I would send the machine back
Completely unusable in that condition- I would send the machine back
Haha. I just got a 3d printer too. So ill have to learn cad sooner than later. I always just fabbed stuff with my tig or mig, vise, hammer, and a grinder. Finally learning the finer tools of fab. Im more amazed with this 3d printer than the lathe, but the lathe seems much more fun. Throwing cad at me is too many new skills at once.
I did draw that at the airport while drinking a beer.
My direct drive motor does surge when its initially loaded, but once its loaded seems to adjust well as torque is needed. Id say better than an untuned vfd with no feedback (like my drill press is) i think its vectoring, and has to be better than a dc motor controlled by only voltage, maybe they have feedback controllers too, but i doubt it.
I did draw that at the airport while drinking a beer.
My direct drive motor does surge when its initially loaded, but once its loaded seems to adjust well as torque is needed. Id say better than an untuned vfd with no feedback (like my drill press is) i think its vectoring, and has to be better than a dc motor controlled by only voltage, maybe they have feedback controllers too, but i doubt it.
- Joined
- Apr 30, 2015
- Messages
- 12,313
The dc drives do have feedback- both current and voltage at least on the KB units I've used
- Joined
- Dec 18, 2022
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ChazzC is 100% correct, If it is new and you already have issues don't start fixing it, just return it. You are with us now and there are a great number of the members here who use that size lathe and would be happy to provide you information on the different brands so you can locate a good machine in your price range. It is a hobby and modifications are part of it but it really should work and provide you with some confidence and experience before you need or, in many cases, chose to work on it.....
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