Switchable Magnets.

[norman6538]

I remember playing with one of these magnetic welding clamps at a welding shop and I thought there was a lot of force required to turn it on and off. That would have to be measured to check for excess work. Then releasing something gains you nothing. Its the attraction where the work done counts and the problem with that is the further you are
away the weaker the force. That feature of magnets puts the potentential work done
on the low side.

But this was my first sight of a truely valid way to turn a magnets force on and off - actually diverting it so it seems it was turned on and off.

If you have one of these then get some measurements and then we'll know if its OU.
I'd really like to see it.

Norman

[Pirate88179]

Here is a very, very crude drawing of what the inside of one of those chucks looks like.
I hate trying to draw using my cheap mouse!

The handle simply moves the entire unit inside toward that empty space (Using a cam/dog attached to the handle shaft) and lines
up the magnets in the base with the steel strips on the top plate. Magnet is now on.

Cranking the handle in the other direction, of course, moves the unit inside so the magnets line up with the brass strips and...no
magnetic attraction any more.

The more I think about this, the more I remember the forces needed to slide that assembly inside, even on a new chuck.  (An older chuck gets much harder)

That handle on the 6" x 18" chuck is about 12" long so, I think it took about 35-40 foot pounds to move it.  We had several women machinists and, they always had to get one of the guys to move that handle for them as they could not do it.

Bill

[Spirit]

https://www.youtube.com/watch?v=cG-01vY36W0

[Pirate88179]

https://www.youtube.com/watch?v=cG-01vY36W0

Spirit:

Excellent find!  Now everyone can see how these are made and can forget my very poor drawing.  I actually have owned about 6 of those smaller Suburban Tool chucks.  Several of them were set up as a sine bar, for grinding angles.

35 pounds of holding power/sq. inch. so, an 8X18" chuck would have 5,040 pounds of holding power!  (I knew it was a lot!)  Our 12x36" chuck would have had 15,120 pounds of holding power!!!!

So now I see that, yes, it is very hard to turn these off/on but, with that many pounds of holding power, surely something could be mechanically or hydraulically worked out and you should have a lot left over to spare.

Spirit, thank you for finding this and posting it.

Bill

PS  I see they are now using stainless steel instead of brass for the dead zones for the flux.  Probably to save money.

[PIH123]

Hi Syncro,

I finally got around to making some measurements.
(promised in the other thread - An Ingenious Way to Turn Neodymium Permanent Magnets On and Off - Magswitch. . .)
I had a welding project going on and didn't want to disassemble the earth clamp.


Details.
Magswitch 300 amp ground clamp part no WG300MS

I used a spring balance to find the force (torque) required to open/close the magnet.

Max required (towards the end of the closing stroke)
5.4 lbs at 1.75 inc dia.
So about 0.4 lb ft.

Same for both Open/Close. (except that the max on open is near the beginning of the stroke)



Next, I mounted the MagSwich in my drill press.
This was so I could carefully position it near the workpiece using the vernier action of the (expensive) drill press.


1st, using a 1.04 lb wrench lying flat and unsecured on the drill press table,
the magswitch in the on position, needed to get to 0.23 inches before the wrench was lifted into contact.

2nd, using a 48 lb tractor (mild steel) tractor weight lying flat and unsecured on the drill press table,
the magswitch in the on position, needed to get to 0.05 inches before the weight was lifted into contact.



Are there any other tests you would like ?

Thanks

Pete