[Mhook]

hi everyone
in my vmc4020 spindle motor , i have
increasing and decreasing rpm!
in low speed gear only
I don't have a problem when the spindle turns on at a speed higher than 2500, but this problem occurs when the speed is lower than 2500 when the spindle motor has more torque and speed.
And the current protector shows that the motor is use too much current
i checked vfd and swap with other vmc 4020 and i check encoder
spindle rotates very smoothly
i checked 3 wires and 2 ohm resistant together and 2 megaohm to motor body

[cncmakers001]

If the motor is use too much current we can check below:

1. Poor spindle lubrication

2. Spindle bearing damage

3. Spindle motor failure

4. The spindle workload is too heavy

[rwskinner]

That display looks pretty strange! I had something sort of like that where my low gear was bogging down and using lots of torque and surging. Mine ended up being the gear change cylinders weren't fully releasing keeping both speeds partially engaged. IOW, one of the belts was only partially releasing and causing drag on the motor. I bled the cylinder and it worked for a while then I finally just replaced both cylinders. I have no clue if yours is the same problem but might want to make sure that is working ok.

[Mhook]

That display looks pretty strange! I had something sort of like that where my low gear was bogging down and using lots of torque and surging. Mine ended up being the gear change cylinders weren't fully releasing keeping both speeds partially engaged. IOW, one of the belts was only partially releasing and causing drag on the motor. I bled the cylinder and it worked for a while then I finally just replaced both cylinders. I have no clue if yours is the same problem but might want to make sure that is working ok.

thx for reply

I checked the both of cylinders and I think they are working properly, the spindle rotates easily
The problem shows itself in 1500 to 2500 rpm

[rwskinner]

On some Fadals, theres a delta / wye relay that controls which mode the motor is in depending on RPM. Maybe it has a bad set of contacts?

[Mhook]

On some Fadals, theres a delta / wye relay that controls which mode the motor is in depending on RPM. Maybe it has a bad set of contacts?

This machine only has an overload relay motor( allen bradly), which may not have worked when drag high current and the motor winding burn out

I looked inside the motor with a flashlight, apparently some of the wires turned black and burned

[rwskinner]

Well, there's your sign! Doesn't sound good.

[Mhook]

Well, there's your sign! Doesn't sound good.

TNX for the info

[Mhook]

Well, there's your sign! Doesn't sound good.

I found the problem, deassembly spindle motor with great effort and checked that all the wiring and bearings worked without problems ! I diassembly encoder and install again the encoder, the error increased tremendously, the pulse disk of the encoder was warped and scratched, which caused the pulse output to be wrong and the spindle driver vfd to be confused because of that! and sent a lot of current to the motor, according to the nxgenparts website, and then I replacing the encoder, the problem was solved

[rwskinner]

I wasn't trying to be a smart ars if that's how you took it. I figured what you were describing was a cooked motor winding when you were talking about black, burnt wires. I'm glad you were able to fix it. The encoder was way cheaper than a new spindle motor.

[Mhook]

I wasn't trying to be a smart ars if that's how you took it. I figured what you were describing was a cooked motor winding when you were talking about black, burnt wires. I'm glad you were able to fix it. The encoder was way cheaper than a new spindle motor.

Thank you for your advice