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

[Grindstone CowboyParticipant @grindstonecowboy]

Apologies for resurrecting my very old thread, but I recently became the owner of a very nice MItutoyo magnetic base, complete with instructions which emphatically state it should be stored “OFF”.

Rob

[SteviegtrParticipant @steviegtr]

Not sure about all this. At school we were were taught to always have a keeper on. A piece of magnetic steel across the north & south poles to keep the magnet in tip top condition. Or were the teachers wrong. Another thought was if a Motorcycle magneto lost its magnetism, Wack it with a hammer to bring it back. But I was always taught that hillting a magnet destroyed it force.

Steve.

[Robert Atkinson 2Participant @robertatkinson2]

The teachers were not wrong.

A switchable permanent magnet base or chuck places a shunt aka keeper across the poles in the OFF position.
You can leave it on with external keeper but unless it is a solid lump of steel, with a flat unpainted surface not a bit of sheet or plate less than 15mm thick, it is unlikely to provide as good a magnetic path as the internal one.
Most magnetic bases still use alloy steel magnets. The properties of rare earth and ferrite types don’t outweigh the cost. Steel ones can be machined to complex shapes and then magetised removing the need for separate pole pieces or supports.
Hitting a magnet can demanetise it but is not a reliable means of magnetising. It needs to be aligned with an external magnetic field.

Robert.

[Howard LewisParticipant @howardlewis46836]

My Magnetic bases have always been left in the OFF position; and are still functioning well after more than 30 years.

On the other hands, pot magnets (used to hold small guards on the machines), and the telescopic stick magnets (In a copper tube for swarf removal) are always stored with a washer or disc as a keeper, when not on use.

Howard

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, here’s my Eclipse No. 903, which is over 55 years old, which has been stored mostly with it switch off, as it tends to return to the off position when it isn’t attached to iron or steel, but it has also had some long periods switched on on steel. It’s holding just a little over 6 kg. Although the surface on the block is flat, it does have very shallow machine marks on it.

The big block weighs a little over 5 kg, and all the other weights sitting on it, add up to 1 kg, with the one on the left weighing 500 grams.

Regards Nick

[not done it yetParticipant @notdoneityet]

Lower the clamp stand a bit, Nick.  The base is most likely cast and may not like a 6kg lump falling on it from even at the height shown!

[Howard Lewis]

On Howard Lewis Said:

………

On the other hands, pot magnets (used to hold small guards on the machines), and the telescopic stick magnets (In a copper tube for swarf removal) are always stored with a washer or disc as a keeper, when not on use.

Howard

Yes, I got one of those at the same time as the Mitutoyo in a box of bits, and it is currently totally non-magnetic. I guess boring a recess and Aralditing a rare-earth magnet into it would be the easiest way to make it useful again?

Rob

[David George 1Participant @davidgeorge1]

I have had magnetic chucks etc re-magnetised by Eclipse. Just drop them in a their factory Sheffield near Meadowhall.

Arundel Business Park,

Claywheels Lane,

Sheffield

S6 1LZ

United Kingdom

 

[Grindstone Cowboy]

On Grindstone Cowboy Said:

On Howard Lewis Said:

………

On the other hands, pot magnets (used to hold small guards on the machines), and the telescopic stick magnets (In a copper tube for swarf removal) are always stored with a washer or disc as a keeper, when not on use.

Howard

Yes, I got one of those at the same time as the Mitutoyo in a box of bits, and it is currently totally non-magnetic. I guess boring a recess and Aralditing a rare-earth magnet into it would be the easiest way to make it useful again?

Rob

It depends on the pole arrangement of the origial magnet. You need to look at that and decide what flux arranemen will work with the new magnet. Pictures would help.

Robert.

[not done it yet]

On not done it yet Said:

Lower the clamp stand a bit, Nick.  The base is most likely cast and may not like a 6kg lump falling on it from even at the height shown!

Hi NDIY, well it didn’t drop off, and it takes just about all my effort to pull it off, which is much more than the 6 kg that is in the photo.

Regards Nick.

[David George 1]

On David George 1 Said:

I have had magnetic chucks etc re-magnetised by Eclipse. Just drop them in a their factory Sheffield near Meadowhall.

Arundel Business Park,

Claywheels Lane,

Sheffield

S6 1LZ

United Kingdom

 

How long ago was that?
They’ve moved now and are down Attercliffe
Atlas Way, Sheffield, S4 7QQ, UK
+44 (0) 114 225 0600
info@eclipsemagnetics.com

I spoke to them just after the first lockdown with a view to having a 10″ round fine pole one fettled, and had a verbal estimate of about £120-150

A few weeks ago I enquired again, to arrange to drop it off  as I was visiting a friend around the corner, but apparently they rarely take on jobs for private customers now, though their answer was friendly and helpful.
I could drop it off, but it might be several weeks before investigation, with a price of £80 + vat to look at and re-certify it.
It’s obvious it would fail, as it’s very weak, but they couldn’t promise to improve the magnetism, and gave no maximum estimate of costs.

Does anyone know how to dismantle one of these; there’s a couple of Youtube videos, but none I could find applicable to this style/make.
Bill

 

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