Magnetic bases – stored on or off?

[Grindstone CowboyParticipant @grindstonecowboy]

Whilst musing in the workshop, it struck me that I've never been told the best way to store a magnetic base – should it be switched on or off to maintain optimum power over the years? Or does it not matter a bit?

Another thing I just noticed is that passwords used to log into this forum are not case-sensitive…

Rob

[Grindstone CowboyParticipant @grindstonecowboy]

Should they be switched on or off for storage?

[Martin KyteParticipant @martinkyte99762]

I would say Off on the basis that the keeps are in place in that state. I'm open to correction if anyone knows better.

regards Martin

[old martParticipant @oldmart]

If you wanted to, you could have a piece of 1/8" mild steel on the bottom and leave them on. The ceramic magnets used in modern rotary switch types are likely to retain their magnetism better than the magnets used in the push on and off types. Mine are all left on stuck on the nearest steel to the mills.

Edited By old mart on 03/04/2021 19:40:19

Edited By old mart on 03/04/2021 19:42:15

[SteviegtrParticipant @steviegtr]

I would have thought in the on position. Look at the diagram. When it is off the magnet is not doing anything. So when on the metal it is adhered to becomes the keeper.

Steve.

[Dave HalfordParticipant @davehalford22513]

I've always left my Eclipse one off – 30 years and counting so far.

[Tony Pratt 1Participant @tonypratt1]

It doesn't matter!

Tony

[Steve NeighbourParticipant @steveneighbour43428]

When mine arrived from the supplier, they were in the OFF state, and one assumes they had been in that condition since manufacture

On that basis, I would vote for keeping OFF when not being used !

Steve

[not done it yetParticipant @notdoneityet]

On that basis, I would vote for keeping OFF when not being used !

Agreed, but as mine are, like old marts, left on the nearest ferrous surface, mine are always on when not in use and on when in use! That way, my expensive dial gauges/dti’s are stored more safely.🙂

[Robert Atkinson 2Participant @robertatkinson2]

If not stuck to something ferrous they should be OFF. This 1/ preserves the magnetisim (less important with modern magnets but who knows what is inside a given base), 2/ It stops the base picking up stray bits of swarf etc.

Likewise magnetic chucks should always be off when not in use. A third reason applies to chucks, safety. They are powerfull enough to cause injury if they "grab" a tool or workpiece with your hand between them.

Robert G8RPI

[Neil WyattModerator @neilwyatt]

Mine came with instructions that said turn it 'off' (when not attached to anything) as this places a keeper across the magnets (and this is why it doesn't stick).

If left attached to a machine bed etc. then you can leave it 'on'.

[Simon Williams 3Participant @simonwilliams3]

+1 for Robert's explanation above.

As far as I can see, no-one has explained that the function of the on/off switch is to short-circuit the magnetic flux in the OFF position, and to remove that short circuit in the ON position. So the "switch" function is analagous to that of a parallel shunt in an electric current circuit. The magnetic flux never goes away, the off position of the "switch" just routes it internally so it doesn't pass through an external object. The switch routes the flux internally in the off position, and routes it externally via the pole pieces in the on position.

Of course the statement that the flux never goes away is a bit of an assumption, and this goes to the heart of the original question. Magnets not made with rare-earth compounds are prone to losing their flux intensity (de-magnetising) if they are left open circuit ("ON" in this application) and without a keeper (Old Mart's bit of steel stanchion). But that goes back to the dark ages, and any magnetic stand made in the last (say) 60 years is not going to be made of materials with such a significant design weakness.

And Robert is also right about the safety aspect of this. Getting your finger pinched in the (reducing) gap between the magnet and its attraction hurts. A lot. With modern rare earth magnets the attraction force at close range can be more than your skin can support, at which point it becomes an amputation. Ouch!

The mathematics of this are simple. For a simple magnetic circuit, the closing force (force of attraction) rises as the inverse cube of the separation. So magnetism is a short range force, and the cartoon characters being sucked onto a magnet over inter-stellar distances weren't paying attention in school physics lessons.

Rgds to all

Simon

Edit – to be fair to Neil his post (while I was typing mine) introduces the magnetic "shortcircuit" concept, so my apologies for saying no-one had explained… etc.  As ever, someone was typing a more succinct and elegant answer while I was still en route.

 

Edited By Simon Williams 3 on 04/04/2021 00:25:59

[Grindstone CowboyParticipant @grindstonecowboy]

Thanks everyone, I shall turn mine OFF from now on.

(I keep it in its nice wooden box)

Rob

Edited By Grindstone Cowboy on 04/04/2021 00:31:47

[Mark RandParticipant @markrand96270]

Posted by Simon Williams 3 on 04/04/2021 00:02:35:Magnets not made with rare-earth compounds are prone to losing their flux intensity (de-magnetising) if they are left open circuit ("ON" in this application) and without a keeper (Old Mart's bit of steel stanchion). But that goes back to the dark ages, and any magnetic stand made in the last (say) 60 years is not going to be made of materials with such a significant design weakness.

 

 

Actually, the situation isn't as good as that. I've got a very good Eclipse magnetic square that's not particularly magnetic at all. The AlNiCo magnet in it has lost most of its strength. It's on the to-do list with a selection of suitably sized NiB magnets and a block of aluminium for a carrier to re-power it. I have a number of other magnetic indicator stands that could probably benefit from the same treatment.

Basically NiB or samarium cobalt magnets will survive anything except being in a fire. Ferrite magnets (the dark grey ones), often used in welding clamps, aren't as strong, but will survive anything but shatter when dropped. AlNiCo can be as strong as the rare earth magnets, but have a low remmnance, and loose much of their strength the second that they are 'open circuited'. There are still quite a few mag bases etc. on the market with the latter magnets inside them.

Edited By Mark Rand on 04/04/2021 21:16:51

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