A Couple of Simple Que's About Machinist Mag Bases 3

[Vermeer]

I am at a loss for the answer to something i feel I should already know. I am a machinist and regularly use switchable magnetic bases to solidly hold indicators in place, but I do not understand how they work. Could someone please explain?
1. What is the composition of the material inside the assembly?
2. How do the constituent parts of the magnet operate to create a magnetic field that essentially can be turned "on" and "off"?
3. (ahem-this is the crux of why I am writing), Once disassembled why is the magnetism of all parts totally lost?
4. I know that the assembly can be re-magnetized. Is this easily acomplished? (With a mag-paricle inspection yoke maybe, or is there some process that can be recomended to experiment with on a small scale?) What references on this subject could help? --Thanks

 

[EdStainless]

I have seen two types. Both use a permanent magnet and can be disassembled and put back together and work fine. They are built with ferrite (ceramic) magnets these days. Many of them used to use Alnico magnets.

One type uses iron pole pieces and a magnet between them. When the magnet is turned to have N on one side and S on the other the base is on. When you turn the magnet so that the poles are not in the magnetic circut it is off.

The other style has the magnet fixed between the pole pieces. In order to turn the base off a piece of iron is placed across the poles to shunt the field.

Corrosion never sleeps, but it can be slowed down.

 

[electricpete]

I have never pulled one apart but I suspect Ed has the idea.

One aspect is that a magnetic flux always travels in closed loops, and can travel much easier through steel than air.

If the loop is broken inside the unit, force will be much less.

One thing I can imagine is that there would be three pieces inside the magnet forming an inverted U. The top horizontal leg the inverted U would be the permanent magnet and the side vertical legs would be permeable steel. In this configuration it will attract to any permeable steel on the bottom. But if I separate the top permanent magnet leg from the two permeable steel legs, there is no more loop through an external piece of steel (flux has to go through air inside the unit).

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[elneilio]

I have come across your topic after much searching of the internet. I wonder, have you found any more on the subject of switchable permanent magnets? I would like to know how they work, how to make them, who manufactures them, anything?

Regards Neil

 

[UKpete]

elneilio, Eclipse are a major manufacturer of magnetic bases over here in the UK:

http://www.eclipse-magnetics.co.uk/

They also make the large magnetic chucks, e.g. as used on surface grinders.
If you want to see the principle of operation of the chucks:

http://eclipse.brclients.co.uk/Downloads/Chuck Handbook.pdf

 

[elneilio]

Thanks UKpete,

I found these links too.

http://www.freepatentsonline.com/4393363.html

http://eclipse.brclients.co.uk/Downloads/Chuck Handbook.pdf

 

[MJR2]

Vereer,
When disassembling a permanent magnet circuit you may demagnetize the magnets. This is particularly possible if your base was built with alnico magnets. There are magnetic circuits which are stable only if charged with the steel pole pieces. Separating them may result in a demagnetization of the PM's