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Discussion Starter · #1 ·
My cnc has a problem with the "z" axis. When I try to page up or page down to move the spindle, I hear a "brrr" sound and the spindle makes a shaking movement but moves up or down a minute amount.

I am using Mach 3 and previously had all axises moving the correct amount and speed. I went to config and motor tuning and the numbers seemed to be ok. I tried lowering them some on velocity and acceleration but this did not improve the problem. When the power is off, one can use the knob on the stepper motor and move the spindle up and down. I looked at the connect between the stepper motor and the ball screw and it seems to be ok and also, this connector does not turn when you hit page up or page down. Just vibrates a little.

Does anyone have any suggestions? A friend did tell me possibly there is a short on the wires going to the stepper.
 

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I would say your friend may be correct, could also be a broken wire or loose connection. Are their connectors at each end (near stepper and electronic box)? If so, I would try disconnecting the cable at each end and check for connectivity on each wire using an ohm meter. Depending on the stepper and driver, there could be 4, 6, or 8 wires in the cable.

If the cable is ok, next thing upstream to check is power feed to the stepper driver from power supply.

What stepper driver is being used. There are certain stepper drivers that are frequently used on Chinese CNCs that are notorious for going bad.
 

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David - Machinist in wood
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Charles, is the X axis cabling close enough to swap connectors with Z? If that's the case you can swap cables and try to jog both. If the problem now moves to X then it's likely your Z controller. If the problem stays with Z then it's likely the stepper motor.

David
 

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Charles, is the X axis cabling close enough to swap connectors with Z? If that's the case you can swap cables and try to jog both. If the problem now moves to X then it's likely your Z controller. If the problem stays with Z then it's likely the stepper motor.
David
If you can swap cables that is easiest. From experience it could be a cold or open solder joint at the connector. That is why you should "disconnecting the cable at each end and check for connectivity on each wire using an ohm meter". Don't assume broken wire, but consider poor solder connection.

Steve.
 

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Discussion Starter · #7 ·
I checked for connectivity on the 4 wires connecting motor to the power box. They are all good. I do not know what stepper driver is being used. Guess I could remove the panel and look to see if there is a name.
 

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Discussion Starter · #8 ·
I took the z cable, after checking for connectivity, and moved it to the y position on the controller. The motor will still not move the fixture up or down. I am thinking it is the stepper motor.

The motor is a 57 two phase, 3A 150N.cm and has 4 wires. I could not find one on Ebay.

Any suggestions for a source for this motor? The company I purchased the cnc is less than helpful for stuff like this.
 
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