A local machine tooling house recently had their yearly "garage sale". I picked up a damaged 8 in. dia. Chekoslovkian made Walker - Pilana permanent mag chuck really cheap. Asside from the fact that it had been stored for years w/o an antirust coating on chuck face, the detail that the on/off key fits into the chuck was sheared off. It appears that the shaft had a collar brazed onto the shaft where the square key fit into the collar to acuate the chuck. I need to dismantle the chuck to remove the shaft and TIG the collar back onto the shaft. Anything that I need to watch out for in dismantling and reassembling the chuck?
Your fingers! I did one a few years ago. There are alot of razor sharp edges, on the ground surfaces. One wrong move with your fingers in the wrong place, it will chop them off. Use lots of non-magnetic wedges, shims to split it apart. Think about every move you are going to make & where your fingers are. That little 1 lb. magnet becomes a 100 lb. very fast.
Others can give you more specific advice, which I would like to hear. I have one more that needs to be taken apart & fixed. I didn't damage myself or the chuck, only because I was very careful, but there were scarry moments. To be quite frank, I'm afraid of the thing.
|| || ||Aribert wrote: ||> A local machine tooling house recently had their yearly "garage sale". ||> I picked up a damaged 8 in. dia. Chekoslovkian made Walker - Pilana ||> permanent mag chuck really cheap. Asside from the fact that it had ||> been stored for years w/o an antirust coating on chuck face, the ||> detail that the on/off key fits into the chuck was sheared off. It ||> appears that the shaft had a collar brazed onto the shaft where the ||> square key fit into the collar to acuate the chuck. I need to ||> dismantle the chuck to remove the shaft and TIG the collar back onto ||> the shaft. Anything that I need to watch out for in dismantling and ||> reassembling the chuck? || ||Your fingers! ||I did one a few years ago. ||There are alot of razor sharp edges, on the ground surfaces. ||One wrong move with your fingers in the wrong place, it will ||chop them off. ||Use lots of non-magnetic wedges, shims to split it apart. ||Think about every move you are going to make & where your ||fingers are. That little 1 lb. magnet becomes a 100 lb. very fast. || ||Others can give you more specific advice, which I would like to hear. ||I have one more that needs to be taken apart & fixed. ||I didn't damage myself or the chuck, only because I was very ||careful, but there were scarry moments. ||To be quite frank, I'm afraid of the thing.
I'm not familiar with these chucks, but I can't imagine an 8" chuck being that dangerous. Very interesting. Texas Parts Guy
The ones that I have are 6x12 in. The round ones may be different. The pole piece is held on the base with allen screws & doweled. The danger comes from, no place to safely grab the pole piece to get it off of the dowels. The magnets want to hole it together. This is sort of the opposite of being "spring loaded in the pissed off position". :-)
I don't know anything about magnetic chucks, but a little about magnets. Anlico magnets can lose a significant portion of their strength if the magnetic circuit is "opened". If possible, try to keep the magnet shunted with a piece of steel when working with it.
If the magnets are ceramic or rare-earth magnets this is not an issue.
How to tell: ceramic magnets are usually black. Alnico looks like metal, usually has a ground finish. Rare-earth can be black or may be nickel-plated. Alnico magnets will generally be longer in the magnetic direction then in a cross-section while rare-earth magnets tend to have more area and less "magnetic length".
I'm glad I asked - I did not expect any safety type of issues. The other (quick and dirty) alternative is to place the round collar into its pocket (only about 0.25 inch deep, collae has an the internal square for the key) into position in the chuck body and TIG the inside of the collar to the shaft of the magnet. I was leary of doing this because I can see small ball bearings in a race within 0.13 inch of where I would be welding the collar to the shaft. Those bearings could get a bit toasty.
I just had another idea as I am typing this - if I drilled and tapped into the shaft that the collar attaches to and then locktite and thread in an extension to the shaft and then weld a lever onto the shaft extension. If I packed the end of the shaft w/ grease I think I could keep much of the drill swaft out of the bearings. I -think- that there would be enough diameter to the shaft that I could tap an M5 or maybe 1/4 inch thrd. How much torque is involved in activating a permanent magnet chuck? I seem to recall haven seen a welded up actuating lever at some auction that I have been to. So what do you think of either welding or drill and tap. If I destroy the chuck I will only be out about $10.50.
If the lever is broken off, there's probably a reason. :-( Mine were rusted inside, looked like they were towed by the boat from china. You may have to take apart anyway. I don't know how the magnets work in a round chuck, turn or slide. The rectangles slide. BTW, is it stuck in the on or off position. Bolt the base to something thats not going to move. (the table) Figure out how to grab the pole piece, so it won't slip. Maybe a sling, chain with bolts that will bind in the bolt holes of the pole piece. Use the quill as the lifting device. ( I don't like this, but it's the only thing I can think of ) It doesn't take much force to split it apart, taping with a plastic hammer. You're safe 'till it is split. Put as much distance, between the pole piece & base as possible. Cover the base with 2x4, & remove the pole piece. Move the base to someplace that is non-magnetic. (floor) When you remove the magnets, wear welding gloves. If you have to grab a magnet, grab it as if it weighs 50 lbs. Get as much distance, as fast as possible, between the magnet and and base.
Putting it back together, will be an experience. Just be careful. The parts will want to go everywhere, except where they should be, & you don't want your fingers there. I found using wood, cardboard, & plastic help. Use that stuff as shims, & push the magnets into place, then pull out the shims & the magnet snaps into place, hopefully somewhere close to where you wanted it. Push & slide parts as much as possible. (safer)
Let us know how this turns out. Maybe some pictures?
I don't want to be an alarmist, & scare the crap out of anyone. Magnetic chucks can be taken apart & fixed. I've done it, & I'm no expert.
I second the comment that if the lever is broken there's probably a good reason for it but, unless it's a modern chuck with ferrite (ceramic) magnets, opening the magnetic circuit (i.e removing the magnets) will partially demagnetise the magnets and they will lose about half their attractive force. This can only be recovered by remagnetising the assembled chuck using pretty special professional equipment.
Ferrite magnets can be recognised by their shape - roughly disk or plate shaped with the length between the two pole faces much shorter than the diameter of the disk or the widths of a plate. Pole faces will be smooth, other faces smooth or slightly rough.
Alnico class metal magnets have a longer aspect ratio with the distance between pole faces about equal to or a bit longer than the diameter/width dimensions. Pole faces will be smooth but the other faces are left rough cast.
If (as is probable) you have metal magnets try real hard to avoid removing the magnets from contact with the chuck body. Identify the direction that the operating lever moves the magnet assembly and use levers or a heavy lump hammer to directly shift the magnet assembly over it's operating range. Once you've freed it by these fairly brutal methods your jury rig fix of the operating lever should work fine.