Z-axis won't jog anymore

[Liv2fish2]

Hi there,

The other day I went to do some finish cutting on a part I had roughed out several days prior. When trying to jog my axes into the correct reference position, my z-axis would not move right away. Eventually it would move in extremely erratic "pulses" when trying continuous jogging. I can't even begin to imagine why this is now happening, unless the motor is going bad or possibly the ball screw is out of adjustment. I purchase this MBD-20 bench mill from CNC Tools & Automation out of Minnesota. I have not been successful in contacting anyone there for a week, so have begin troubleshooting for a fix on my own. (I'm very new to CNC milling and this is extremely frustrating!) My machine is based on a Rung Fu (sqaure column) and has been in use periodically for 2 months. It has Geck 320 drives, Reliance DC servo motors (1/2 hp for Z-axis), and uses a US Digital rotary encoder. Just for the heck of it, I switch to connections of the z-axis motor & the y-axis motor to determine if it was a bad control board or drive. The y-axis moved normal when plugged into the z-axis connection. The same was not true for the z-axis plugged into the y-connection. It still "pulsed" or moved very erratic. This leads me to believe that my control boards and gecko drives are fine. I have not received fault codes, and no fuses are blown. I would greatly appreciate any help on this. Thanks!!

[Al_The_Man]

The problem appears to be in either your motor or encoder.
You could try hooking the motor to a direct DC source such as aDC power supply or a auto battery to see if it runs ok in both directions. Check the brushes also, if they have worn down to the springs, this could be your problem.
If it checks out, try swopping the encoder with one of the other axis.
Al.

[Liv2fish2]

Thanks Al. I did check the motor for proper operation and it is fine. The brushes look new as well. No carbon build up either. I also disconnected the motor and pulley system and can move the mill head up and down by just turning on the the main drive pulley - no binding at all. I will try swapping out the encoder next. Hopefully that will be the issue. Those are only about $50 and should be under warranty.

[Liv2fish2]

Well, it appears that I got the problem taken care of. My rotary encoder's optical disk had some oil smudges on the disk, which I very carefully cleaned. I also found a loose set screw on my motor's drive pully which caused quite a bit of pulley movement. After cleaning the encoder and tightening the pulley, everything seems to work great. Amazing how the slightest bit of slop can throw off these digital encoders...

[Al_The_Man]

BTW. One of the best ways to clean Encoders and linear slides is with pure alcohol and lens tissue.
Al.

[Liv2fish2]

Yep. That's exactly what I used. Worked great. Although I think the motor pulley was the actual culprit. Thanks for the input.