PM 932 mill power feed problem

[rherrell]

The power feed on my X axis is acting up. It works fine in rapid traverse but it's real slow in the regular mode. If I turn it all the way up to 9 it runs about as fast as it used to go on 3. It also kind of surges a little, like I'm messing with the speed dial.
I backed the gib all the way off and it didn't help, I also checked the gears and everything is meshing fine. I'm no electronics expert but it sounds like maybe the speed pot is dying... any ideas?

 

[higgite]

I'm no electronics expert but it sounds like maybe the speed pot is dying... any ideas?

That would be a good guess. I had a mini lathe that acted that way, erratic speed control, would slow down and speed up on its own. I replaced the speed control pot and the problem disappeared. Before you change it out, though, you might want to try vigorously turning the knob back and forth a couple of dozen times with the machine turned off and then see if that helps. The problem could just be corrosion. If so, and if the pot isn't sealed, some aerosol contact cleaner might be an easy fix.

Tom

 

[Bob Korves]

It probably goes without saying, but make sure the table travel is not too tight for some reason -- lack of lube, gib adjustment, or lock engaged. Sometimes when people get a power feed, they forget they have handles as well...

 

[navav2002]

If it's an asong (or similar) here's a couple of links for parts (just in case):

http://www.cal-metrics.com/insulatorbrush.html

https://www.bestlinepro.com/power-feed-parts.asp

 

[rherrell]

I took it apart and inspected it, nothing jumped out at me but if it's an electronics problem I wouldn't see it. I sprayed it with some cleaner and put it back together and nothing changed.
I took some photos just in case maybe someone sees something I don't.

 

[higgite]

Does the handwheel turn and table move easily and smoothly with the power feed disconnected/disengaged so there is no drag from the power feed? That should at least tell you if it's in the PF or if the table is binding.

Tom

 

[rherrell]

The gib and the locks are all loose, the table slides easily by hand.

 

[Bob Korves]

Those drives have shim packs to adjust the motor gear with the lead screw bevel gear mesh. Is the motor also slow when removed from the machine? If not, then the shims may not be enough, causing binding. If you have that issue, I think I can supply you to a link for setting up Servo drives, which yours is likely mostly copied after.

 

[mksj]

Most likely a bad speed pot, if the wires disconnect you can check it with an ohmmeter and should be able to see an even change in the resistance. I would start with that first. This is very common in speed pots. I often use a wire wound pots, just find them to be more reliable in this setting.

 

[Bob Korves]

Most likely a bad speed pot, if the wires disconnect you can check it with an ohmmeter and should be able to see an even change in the resistance. I would start with that first. This is very common in speed pots. I often use a wire wound pots, just find them to be more reliable in this setting.

Yes, the OP did say it ran fine in rapid...