Fadal VMC inconsistant spindle speed

[MadPickinSkills]

Hello,
Has anyone ever had an issue with the rpm on a Fadal VMC fluctuating at higher rpms? If I specify 7500 rpm and then start the spindle, it will fluctuate drastically. Anywhere from 3500rpm to 7500 rpm. I was told it could be an encoder issue, but I thought I would see if anyone else has any experience with the issue.

[Tedger]

We have a 1999 4020 that did the same thing.Thought it was the belts at first but ended up needing a new optical encoder on the spindle motor.The old one wasn't sealed very well and became very dirty.The new one was sealed much better.You should be able to get the part easy.I installed the new one myself with no trouble,but I didn't run the new wire in the exact location of the old one.
(It ran through the motor housing.)
Good luck

[alex gitzel]

yes you will definetly want to start with the encoder.If you want to check the control input go to the spindle drive and use a multimeter to test dc voltage on pins 4+6 on the 6 pin molex plug that has 6 wires in it(4+6 are the small gauge wires,test top+bottom ones/red+black)the voltage will be between 0-10vdc depending on programed speed,you are looking for the voltage to be stable and not bouncing around a lot.if the voltage is stable the output from the cnc control is good,you can also ohm the motor wires they should be around .6ohm to .05ohm leg to leg.and open to ground(or 0,o/l) if there is current to ground the motor needs rebuilding.but most likely it is the encoder.

[Antonio Arguijo]

Hi!,
We have a machine FADAL 906-1 4020HT
Serial 941164, but the RPM aren't the programed, that's means if I demand 1000 RPM the spindle rotates at 500 RPM (50%) less that the programmed.

do you think hat it's the same problem?

[alex gitzel]

is the spindle consistantly at 50% or does it vary? if it is always 50% look into the spindle override switch,maybe it is set at 50% or was set at 50% and did not go back to 100% when it was moved,possibly a bad switch.does the c axis on the control readout read 100% (some machines do not have this feature)?.If the encoder is bad usualy the load meter will bounce around along with the speed.another possiblity is a bad control card.