Machinist's Magnetic Bases Query 2

[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 hold indicators in place. How do they work? Here are a few questions I have had:
1. What is the the composition of the material which rotates inside the assembly?
2. How do the constituent parts of the magnet operate to create a magnetic field that can esentially be turned "on" and "off"?
3. This is the crux of why I am writing -ahem- Once disassembled why is the previously strong magnetism totaly lost?
4. I know the assemblies can be re-magnetized; can this easily be done? What can be experimented with to do this on a small scale? (Using a mag-paricle inspection yoke maybe, or is more power needed?) Does anyone know of a good practical reference book on this subject?
Thanks--I'm real interested in any replies.

 

[metman]

I can only guess at one of questions whch is no. 2.

I suspect that the rotation device is a permanent magnet that simply aligns and misaligns its poles with surrounding ferromagnetic material so that the magnetic path is made continuous/discontinuous. The ferromagnetic material could very possibly be nearly pure Iron. and the magnet possibly magnetite (I have forgotten what this is but think it is a naturally occuring compound).

hope this helps Jesus is the WAY

 

Thanks, This is precisly what I thought, (else I would not have removed it), but consider this: When the "magnet" in the middle is taken out, all the magnetism of both parts disapears--does not reinstate itself when reassembled, this effecitvly ruins the magnet. But isn't the nature of a feromagnet to maintain its strength?
I suppose that the product could be magnetized as an assembly in the ON position, and I accept the proposition of the switch acting to align/cancel the poles. My guess is that the housing is iron. The part inside is dark grey and brittle-hard; maybe magnetite?
I have searched the net best I can, asked Mecahical engineers, still no answers to the 70 dollar question:
How can one remagnetize a magnetic base indicator holder?

 

[metman]

Is it Bermeer or Vermeer? make up my mind please.

Another thought occurred. Did yu by chance drop the permanent magnet while dissembled? A shock load or blow to a permanent magnet can dramatically reduce its magnetic strength.

Leonard Jesus is the WAY

 

[bvaandr]

Magnetite is a hard brittle material that does not easily lose it's magnetism, even when dropped. If you experience a loss of magnetic "power" in your base, most likely it is because you have put one of the magnetic elements in backward or upside down. One way you can check out this theory is to seen whether you can actually get the maget to turn off - if you can't, then it is certainly misallignment. Make sure that when the internal parts are rotated to "turn on" that all the magnets have their N and S poles pointed in the same direction. You can determine the polarity of the magnets very simply with a compass held near each element once you have dissasembled it. The compass' arrow indicator always points to the N pole (either the earth's or a nearby magnet's).

 

[Vermeer]

Back to Vermeer now. I wrote that last(long) post, and only at the end realized I had not signed in...another story. OK.

Three Things,
(Then I'm going to the Magicians Only Site--and starting the same thread
1. I suspect the material in the middle is magneite, but immediatly after pulling it out of the housing it has a nearly total loss of magnetic strength (as does the housing).
2. No shock. No heat. 50-80lb force prior-->5-8Lb after.
3. Never leave well enough alone/baffeled. Taking apart a second magnetic base the same loss of magnitism happened. I definatly reinserted the part in its original orientation.
There was no miraculous reinstatement of magnetism to the whole.
And I thought you were only a virgin Once!

 

[gphatch]

Please post if you are still interested in an answer to this "conundrum".

Thanks

Gareth Hatch
Dexter Magnetic Technologies Inc.

 

[metman]

gphatch,
You must be the magi. Com-on, out with it. Almost year is long enough to wait for the answer.

Sitting on pins and needles. Jesus is THE life,
Leonard

 

[gphatch]

Okay, to answer the original questions:

1. What is the the composition of the material which rotates inside the assembly?

This material is typically Alnico magnet material. It is an older magnet material type. it doesn't have particularly good resistance to demagnetization, which can occur if you do not remove such a magnet from its ferromagnetic surroundings in an "optimum" manner. For this reason, many assemblies containing Alnico magnets are magnetized AFTER assembly.

2. How do the constituent parts of the magnet operate to create a magnetic field that can esentially be turned "on" and "off"?

The "secret" here is that the bottom surface of the device is typically designed to concentrate the magnetic flux density generated by the magnet, into a small area of contact. It does this when the magnet is in the "on" position - the flux flows from one pole to the other, through the steel part it is resting on. The unit is designed so that when the magnet is in the "off position", when the magnet is physically rotated to a particular position, the flux prefers to loop inside the device from one pole to the other, rather than going externally through your piece.

3. This is the crux of why I am writing -ahem- Once disassembled why is the previously strong magnetism totaly lost?

This is a combination, perhaps, of the disassembly "knocking down" the magnet, and of the fact that the magnet, even in the fully magnetized condition, will not generate as strong a pull force as you would by concentrating the flux it generates through narrow pole pieces.

4. I know the assemblies can be re-magnetized; can this easily be done? What can be experimented with to do this on a small scale?

Typically you would need to re-magnetize such a magnet in a solenoid - on an industrial scale magnets are generally magnetized using such solenoids that are hooked up to capacitance-discharge machines, which pump a lot of current through the coil for a split second. You have to watch when doing this for Alnico magnets, as you can sometimes get a "back pulse" at the end of the pulsing cycle that will slightly demagnetize the magnet. So, you need specific equipment for Alnico. You could try using other stronger permanent magnets to re-mag it, but that would be difficult - and you still have the problem of re-assembling it properly.

Also remember that the magnet is probably not as strong as you think it would be, even when fully magged, for the reasons given above.

Hope that helps!

Gareth Hatch
Director of Technology
Dexter Magnetic Technologies Inc.

 

[gphatch]

One other point - there is a rule of thumb that the pull force a magnet or magnetic device exerts, is proportional to the area, multiplied by the square of the flux density at the pole faces. So although a reduced area would tend to lower this value, increasing the flux density by making pole pieces narrower [thus "squishing" more flux into a given area] more than compensates because of the squared effect.

Gareth Hatch
Director of Technology
Dexter Magnetic Technologies Inc.