Magnetic Chuck - Testing and Troubleshooting Questions

[joe_m]

Life is about to get in the way of my hobbies again, so if anyone responds it will be a few days until I can get around to thanking you. Until then, I leave you with a couple of questions on magnetic chucks - specifically the ones where you throw a lever (manual?) to operate, not electronically charged.

Question 1: How strong should these things be?
A. They should hold a metal object but you can pull it off with just about as much force as it takes to remove a playschool letter magnet from the fridge. (M is for Machinist).
B. So strong that if you bend over to get a close look it will pull the metal plate in your head out through your nose.
C. Somewhere in between A and B.

Question 2 depends on the answer to Question 1.
If you answered A above - no problem, nothing to see here, move along.
If you answered B above - what are the usual suspects to check when it stops working correctly? (Short of mailing it off to a professional for rebuild).
If you answered C above - could you provide a criteria that is measurable using items commonly found in a hobbyist workshop devoid of thousand dollar nuclear, ultrasonic, magnetic microwave measuring devices.

Thanks in advance.
Joe

 

[Ray C]

The answer is C -kinda... If you have say a 3x3" piece of metal, you shouldn't be able to budge it.

I've rebuild many of these things and there's only a few ways they go bad and most can be repaired.

1) There's a cam, lever and pin in there to slide the internal plates together. Sometimes something wears out.
2) The lamination that holds the plates together has cracked. Sometimes it can be pinned back together -sometimes not.
3) Someone has demagnetized it with some other device. -It's a doorstop now.
4) The internal oil is contaminated with a huge amount of swarf and magnets won't align or the magnetic field is rerouted through it. -Just needs cleaning.
5) The top plate is very uneven and dinged and metal pieces can't be set flat on it. -Needs to be milled and reground.

And that's that!

Ray

Life is about to get in the way of my hobbies again, so if anyone responds it will be a few days until I can get around to thanking you. Until then, I leave you with a couple of questions on magnetic chucks - specifically the ones where you throw a lever (manual?) to operate, not electronically charged.

Question 1: How strong should these things be?
A. They should hold a metal object but you can pull it off with just about as much force as it takes to remove a playschool letter magnet from the fridge. (M is for Machinist).
B. So strong that if you bend over to get a close look it will pull the metal plate in your head out through your nose.
C. Somewhere in between A and B.

Question 2 depends on the answer to Question 1.
If you answered A above - no problem, nothing to see here, move along.
If you answered B above - what are the usual suspects to check when it stops working correctly? (Short of mailing it off to a professional for rebuild).
If you answered C above - could you provide a criteria that is measurable using items commonly found in a hobbyist workshop devoid of thousand dollar nuclear, ultrasonic, magnetic microwave measuring devices.

Thanks in advance.
Joe

 

[RWL]

Ray. I may be hijacking the thread. How do you open one of these up and how do you keep the magnets from losing their magnetism once you've got it open?

 

[Ray C]

All the ones I've encountered have about 8-10 socket screws on the bottom. Flip it over, remove the screws and separate the halves. Do the work inside of a big aluminum turkey basting pan or tray because they're filled with heavy weight oil. -And I guarantee it will be nasty and contaminated with swarf and coolant. Contaminants enter through the O-ring seal on the handle. It may take some jigging of the handle and sideways manipulation to get the handle actuating pin out of the internal cam/lever. There will be several leaf springs inside under low tension. Those only ensure the internal plate stays in-contact with the bottom of the top plate.

The internal plate is just a smaller version of the external top-plate. Each plate is a laminate of North/South permanent magnets. The internal plate just slides against the bottom of the top plate. In one position, the magnets align and cancel-out and the other position, they align the magnetism additively. Don't separate the two halves (it would be next to impossible) as there is no reason to.

Clean all the gunk out, wash everything in the parts cleaning tank, make or repair any worn cams or actuating levers etc. fill with NON-detergent heavy weight oil (Way oil, hydraulic oil etc) and reassemble. You want non-detergent oil because the laminated plates are pinned together and also have an epoxy sealer. Err on the side of caution and assume that detergent oil could break-down the epoxy. There's anywhere from a pint to a quart of oil depending on the geometry of the unit. I always re-bore the hole that the handle pivots through and I re-make the shaft that goes through. This usually involves remaking the cam or cutting off the shaft and TIGing a new shaft onto it. The passage way for the handle pivot is almost always beat-up marred and just putting a new seal in there is just cheating the customer since it wont last long.

BTW: For anyone who owns a mag chuck, it's not a half bad idea to flip it over on it's topside for just a few moments once every blue moon or so. This will ensure there's a film of heavy oil between the plates to ensure smooth operation.

If the bottom plate is cracked, they can be repaired (sometimes) by pinning an aluminum plate to hold the pieces together. Perfectly legitimate way to fix them. I had two this way and to be on the safe side, did not re-sell them. They are my shop chucks and work fine.


Oh, surface grinding the top and bottom... Just mill the bottom flat. Flip it face down on the table and activate the magnet. Take off as little as possible. Flip it over and true-up the top side with a GOOD face cutter. Use the inherent hold down clamps to hold it in place. Don't try to remove any dings that are too deep (judgement call). Throw it in the surface grinder and do the top only. It's not easy (and you'll find-out just how imperfect a mill cut really is). Do no more than a 0.010 step with no more than half thou downward. Takes 2 hours usually to do the top. Don't let anything get hot unless you're running coolant. If you feel heat, it will not be flat and square. The ones I've done came-out within a few tenths (measured on the granite and TDI) from corner to corner.

----More than you wanted to know but now you know it and can restore life to things... They look almost brand new when done.

Ray


EDIT: Hint. When you SG the top and if you dont run coolant (I don't), preheat the entire chuck to about 150degrees in an oven. This will keep your starting and terminal temps about the same; otherwise, you'll be chasing your tail to keep the tenths in line.

Ray. I may be hijacking the thread. How do you open one of these up and how do you keep the magnets from losing their magnetism once you've got it open?

 

[RWL]

Thanks for the description. There are a mixture of posts on the net about magnetic chuck repair, but nothing quite as specific as your description. If you happen to have one open at the moment, can you shoot a picture of what they look like inside? Mine is working, but getting harder and harder to turn the lever. The magnetism doesn't seem even over the entire top, and doesn't quite go away as much as I think it should would when it's in the off position. What I'm somewhat concerned about repairing is the actuating mechanism. My lever is at the long end rather than along the side, and I suspect it works on a helix in the shaft. Replacing that could be a problem. The chuck is by Magnetool of Hazel Park, MI. They're still in business, but whether parts are available is another question.

 

[Ray C]

Sorry to say, I don't have one open at this time and I'd prefer not to open one gratuitously since that would pretty-much blow the surface grinding job since the two halves wouldn't go back together exactly the same way. If another comes along, I'll take pictures. I got my hands on a bunch of abused ones for cheap and rebuilt them all. I'd never opened one prior to that so, I just had to figure it out. There is no rocket science at all.

They all suffer the same symptoms you describe but you won't know what's wrong until you see the guts.

I view your situation as win-win by taking it apart... At the moment, you have a dysfunctional device that's not safe to use for surface grinding -you can't make it much worse and only stand to possibly find something simple to fix. If things look really screwed-up, take pictures and post them and we can assess the problem. It's gotten to be common knowledge by now that folks often send me stuff to make and if it can be done with shop-drops, all I ask is that you pay postage both ways. If it's something I can make, I'll let you know.


Ray

Thanks for the description. There are a mixture of posts on the net about magnetic chuck repair, but nothing quite as specific as your description. If you happen to have one open at the moment, can you shoot a picture of what they look like inside? Mine is working, but getting harder and harder to turn the lever. The magnetism doesn't seem even over the entire top, and doesn't quite go away as much as I think it should would when it's in the off position. What I'm somewhat concerned about repairing is the actuating mechanism. My lever is at the long end rather than along the side, and I suspect it works on a helix in the shaft. Replacing that could be a problem. The chuck is by Magnetool of Hazel Park, MI. They're still in business, but whether parts are available is another question.

 

[RWL]

I'll take you up on your offer to trouble shoot photos. It may have to wait until this weekend. By the way - turn the magnets on or off before taking it apart? I've read that the two halves are joined tightly. What did you use to wedge them open a little - knife blade?

 

[Ray C]

Magnets disengaged for disassembly -or it will never come apart.

Don't bother separating the two halves. If the top plate is cracked, it's toast anyhow because you certainly cannot fix it from the exterior top side and it cannot be repaired on it's other side as the bottom plate needs to make flush contact. If the bottom plate is cracked, depending on where it's cracked and the space you have to do the repair, it can be done as an assembly. The residual magnetism holding the pieces together is considerable and you'll likely hurt yourself or break the epoxy getting them apart. I suspect it's done with a large sliding fixture of some sort with hydraulic or other mechanical means of leverage. When you see what's inside there, you'll see there's no reason for further disassembly -trust me on this...

You will need a parts cleaning tank with some light solvent cleaner or even some rubbing alcohol as well as compressed air to blow it all dry.

I had one where an area of the bottom plate where the pin that goes through a swivel-pinned lever was worn out. I just built it up with TIG, reformed the area and re-drilled the hole. I was in and out with the TIG in under 10 seconds and the heat never traveled. On that unit, I also had to re-make the cam that was worn to nothing. Good as new! I often wonder how many hundreds-of-thousands of times that was operated to wear it out so bad.


BTW: I'm reasonably well convinced that the reason these things break in the first place is because nobody every flips e'm over once in a great while to let the oil lubricate the upper half of the internals. -And that's why you want to use really heavy oil; so it sticks up there for a long time. -Just my theory from seeing the insides of about 7 of these things. I just took a gamble, bought a bunch of broken ones on the bet I could fix e'm and flip e'm and I came out with Aces.

Ray

I'll take you up on your offer to trouble shoot photos. It may have to wait until this weekend. By the way - turn the magnets on or off before taking it apart? I've read that the two halves are joined tightly. What did you use to wedge them open a little - knife blade?

 

[RWL]

I've got the chuck opened but how do I get the top disengaged from the linkage? I think that's what's holding it in place. The actuator is at one end of the chuck. I can lift the top / magnets up about 3/8" at the end opposite from the actuator, and only slightly at the actuator end. There is about 1/8" of space between the magnets and the sides of the case, except at the end with the actuator, where there is a little more space. Note again that the actuator is at the end, and not along one of the sides. Photos below. . In the last photo, the screwdriver is in the end opposite to the actuator.

 

[Ray C]

Look'n good so far. Yeah, they're reluctant to come apart. All the ones I've done had the handle on the side, not the end -and they had a cam with a pin on the end of the handle shaft. The pin fit into a lever. You had to move the base sideways to get the pin out of the lever hole. Sometimes the pin is worn and it forms a groove so it doesn't easily slide out of the lever hole.

Since yours is a little different, I'd have to see it. Look in there with a flashlight. Admittedly, the first time I did this, it had me scratching my head but once you've done it, the rest are a snap.

Was it filled with gunky oil?

Ray