# PM 932 mill power feed problem



## rherrell (Oct 7, 2017)

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 (Oct 7, 2017)

rherrell said:


> 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 (Oct 7, 2017)

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 (Oct 7, 2017)

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 (Oct 7, 2017)

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 (Oct 7, 2017)

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 (Oct 7, 2017)

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


----------



## Bob Korves (Oct 7, 2017)

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 (Oct 7, 2017)

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 (Oct 7, 2017)

mksj said:


> 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...


----------



## rherrell (Oct 8, 2017)

Bob Korves said:


> 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.


I didn't get any shims with it, it adjusts by moving the metal angle plate it's mounted to either up or down. I guess shims could be used to move it out but that appears to be a good fit.


----------



## rherrell (Oct 8, 2017)

mksj said:


> 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.


That's easy for YOU to say Mark!  My electronics skills are next to none so we'll save that as a last resort.


----------



## qualitymachinetools (Oct 8, 2017)

Check the motor brushes. We have spares if you need them, thats what it sounds like.

 Usually when it happens its gradual, so people think that its going full speed in rapid, but its actually a lot slower than it was at the beginning.      Just a guess, the others could be right with the speed pot, but the brushes are something to check


----------



## dlane (Oct 8, 2017)

On servo brand PFs the rapid is a separate circuit from the speed pot


----------



## mksj (Oct 8, 2017)

Rick,
After you check the brushes, if you still have a problem, I would suggest the following:
In the picture below, there is the speed pot on the left with 3 wires connected to it, yellow, white and blue.  These wires are connected to the control board with a 3 pin female socket which you should be able to carefully slip off the pins on the control board (Power disconnected). Once the socket is disconnected, use some thin bare wire or pins and stick them in the 3 socket holes to make connections. You can measure the total pot resistance using an ohmmeter between the wires/pins connected to the yellow and blue wires, white wire is attached to the wiper which adjusts the resistance. So use an ohmmeter attached to the yellow and white first and sweep the pot, the resistance should evenly change with no jumps or sudden changes. Repeat this between the white and blue leads. If the pot does need to be replaced, you need to measure the total resistance of the pot, and its basic dimensions. They tend to be fairly standard in size. Remove the old pot unsolder its wires and resolder to the new pot noting the same wire connections. If the pot checks out fine and the brushes look good, then it is probably a problem on the control board.


----------



## rherrell (Oct 9, 2017)

Deleted


----------



## rherrell (Oct 9, 2017)

I measured both sets of wires and got the same readings, 0.000-0.536. It seemed like it was smooth going up and down.






Does this mean the pot is good? There are no markings on the outside of the pot so I can't give you it's rating.


----------



## rherrell (Oct 9, 2017)

I just ran it with the case open and it will barely do anything. It runs fine in rapid traverse but almost nothing in regular mode. It almost feels like the switch in the handle is bad, if I play with the handle it seems like it wants to start but then it quits. I can't get it to run in regular mode for more than a second or two.


The brushes look fine to me...


----------



## rherrell (Oct 9, 2017)

OK, I just reassembled the unit and now the handle seems to work, the speed still oscillates up and down but at least the handle works!


----------



## rherrell (Oct 9, 2017)

Matt seems to think it could be the brushes, he's sending me some so I'll get back to you after I try them out.


----------



## mksj (Oct 9, 2017)

rherrell said:


> Does this mean the pot is good? There are no markings on the outside of the pot so I can't give you it's rating.


The pot is a 5K unit, they are often +/10%. Seems like the pot is OK if when you sweep up and down with one lead connected to the wiper and the ohms  evenly change without jumps or skips. Brushed do not look bad either. When you take the bushes out you might blow some air at light pressure in the brush holders to clear any dust from the bushes, sometimes I lightly sand the contacts with very fine sand paper or a contact file to clean any oxidation.  On my drive there are switches for each direction that kick in when the lever is switched into forward/reverse, but I would not expect both directions do go at the same time. That it is intermittent and getting worse, might be a component failure in the speed control circuity or an intermittent connection, could be the brushes but doesn't explain why it would work with the high speed button.


----------



## rherrell (Oct 9, 2017)

Matt said the brushes are .625" new, mine are .536", not bad but he's sending me some new ones to try. He said the spring could be weak and I agree, that was the first thing I noticed when I removed them. If the brushes don't fix the problem Matt said to send it to him and he will repair it, great CS...as always!!!!


----------



## 38Bill (Oct 13, 2017)

I had exactly the same thing happen on my 932. Matt suggested I check the brushes so I did. Didn't find any problem but the power feed has worked fine ever since??????


----------



## qualitymachinetools (Oct 17, 2017)

It wasn't the brushes, so just sent a new one, hope that takes care of it.


----------



## rherrell (Oct 19, 2017)

UPDATE......  Like Matt said, he sent a new power feed and everything is working fine again. THANK YOU Matt for all your help and the GREAT customer service!!!! Also, THANKS to all of you who commented, I love this forum!!!


----------

