Rebuilding Surface Grinder Chuck

I have a OS Walker chuck with a Minatron control that will not always release parts. I finished up a part the other day, had a really nice grind on both sides of a die detail, and it wouldn't let go. I wound up having to beat the thing off with a dead blow and scratched up my nice grind. That was AFTER turning it back on at 0.

To be completely honest, I do not know anything about electromagnetic chucks. I have always had a "mechanical" magnetic chuck in my shop, though I have used many surface grinders with electromagnets.... they always let go.

So where does one start?

I found several threads discussing WEAK magnets, which this is absolutely not.

One thread mentioned checking the connections. Will take it apart and check connections.

Control is 120v, 2amps, DC 0-115, 1.3amps

Sounds like you have an issue in the controler. When you turn the chuck off it should go through a demagnetize routine. It puts 60 cycle electricity through the chuck coils and demagnetizes the part so you can just pick it up.

There could be a fuse or relay blown in your controller.

When you demag put your volt meter on C1 and C2 wires, normally this is how they are marked.

Say you have a 120V chuck you will see it "step down" the voltage.

REMEMBER YOU ARE DEALING WITH DC VOLTAGE. BE CAREFUL WHEN DOING THESE CHECKS. DC DOES NOT LIKE TO LET GO OF YOU.

So for example.

120V- 0V

100V-0V

80V-0V

60V-0V

40V-0V

20V-0V

so this would have been 6 steps. the closer or more steps you get to 0V the more your parts will be demagnetized.

Took a couple pictures so you guys are guessing.

Chuck

Control


Opened up the control to take a look. First things first, I did check the fuse, and it looked NEW. I could not find wires marked C1 and C2, but looking at the control (upside down in the picture) the box with 6 terminals is the ON, OFF, RELEASE switch.

With the switch in the OFF position the terminals read 33vDC(ON), 0v(OFF), -64vDC(RELEASE)
With the switch in the ON position the terminals read 32vDC(ON), -62vDC(OFF), -62vDC(RELEASE)
With the switch in the RELEASE position the terminals read 33vAC(ON), 32vAC(OFF), -64vDC(RELEASE)

With the switch held in the release position the voltage across the three sets of terminals stays constant. Though I only held it for 8-10 seconds.

On many such control setting to release position only releases for a moment then re-holds the part..
It is not uncommon that you may have to switch to the release side for only a moment to release.
I hold the part with push pressure and bump the release side to feel the part let loose.

qT: Setting a part on copy paper can be a good idea for saving a chuck finish.

I don't think this is operating correctly. The electromagnetic chucks I have used at shops I worked at would do similar to what you are saying. Flip the release switch and apply upward pressure, after a brief time the part would release. If you didn't get the part off the chuck during that time though, you would need to hit the switch again.

I had my wife come out to toggle the switch while I picked up on the part. We tried several combinations including her holding the switch and could not get it to let go. I was picking up with all I could grip on the part, which was enough to start to pick the grinder table off the saddle.

I used to get made fun of at a shop I worked at for putting a piece of paper down to protect a ground surface on a chuck that had issues. My grandfather taught me that when I worked for him.

I used the IBM cards for under a part on the chuck.. you dont see them any more.
You might have to send the controller out..perhaps a local machine seller knows / has a guy.

Magnetic Chuck Services | Repair and Rebuild Magnetic Chucks and Controls

This shop north Of Detroit

I have an older Walker chuck with a Walker control... not sure if it's the same control. But what I find is if the part won't release I turn the reaostat down while holding the release toggle down normally does the trick. Or I reset the holding power real low then turn the control to release. Works for me.
Dennis