Confused by a magnet

[Robin GrahamParticipant @robingraham42208]

Posted by Michael Gilligan on 18/12/2022 08:09:14:

Thanks, John … but it appears to be a casing rather than just a plating-job

MichaelG.

I'm confused as well now – looking at the Zoro site I see:

"Manufactured from neodymium iron boron 'rare earth' material, this range of magnets offers superb hold due to its construction from the strongest magnet material available. With an impressive 80°C maximum operating temperature, each product is zinc plated and features a countersunk hole. […] "

My emphasis.

What I can say for sure is that zinc is diamagnetic and can't really play any significant role in 'completing the magnetic circuit'. It seems likely that it's there as an antidote to corrosion.

It's certainly true that rare earth magnets are sintered and very susceptible to corrosion creeping in through grain boundaries – that's why they are usually plated.

In my experience rare earth 'pot magnets' have a rare earth magnetic core surrounded by a more robust ferromagnetic case which serves to protect the rare earth magnet from shock and also , if the case extends beyond the face of the magnet, to somewhat 'focus' the magnetic field. That's good in some circumstances – it depends on the application – whether you're after holding or attracting perhaps.

Robin

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Robin Graham on 20/12/2022 01:03:25:

[…]

In my experience rare earth 'pot magnets' have a rare earth magnetic core surrounded by a more robust ferromagnetic case which serves to protect the rare earth magnet from shock and also , if the case extends beyond the face of the magnet, to somewhat 'focus' the magnetic field. That's good in some circumstances – it depends on the application – whether you're after holding or attracting perhaps.

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Thanks for your thoughts on this, Robin

Regarding your closing line … The truth is, I ordered Qty.3 from Zoro [on ebay] because they were relatively inexpensive and looked like they might ‘come in handy’

It will be interesting to see how they are packed for postage … My last Zoro order arrived in a vastly oversize plastic mailer, and I have visions of such being firmly attached to the van by 31.5Kg of magnetic attraction

The musings on this thread have been interesting, but would probably have been unnecessary if the Eclipse literature was more informative … The document kindly linked by Bill [Peak4] is little more than a ‘glossy brochure’ and, for this range of products in particular, the explanation of construction-and-use is sadly lacking. … They do offer one version in a range of pretty colours though !!

Happy Daze La-la-la

MichaelG.

[Martin WParticipant @martinw]

Michael

I don't think that this magnet is a potted variety. The magnetic material has been formed with a stepped rim to allow it to make a more effective contact with uneven surfaces and give clearance should the fixing screw head be slightly proud of the countersunk hole. If so then the description given by Eclipse is correct in so much that it just a rare earth magnet with zinc plating for protection.

It will be interesting to see what eventually you receive. I too have ordered rare earth magnets and they were packed wrapped in layers of bubble wrap in large boxes. If sent in thin wall packing I have visions of delivery company staff desperately trying to peel the package from machinery or the side of delivery vehicles, and god forbid that two such packages addressed to different recipients ever became attached to each other!

Martin

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Martin W on 20/12/2022 11:14:14:

Michael

I don't think that this magnet is a potted variety. The magnetic material has been formed with a stepped rim to allow it to make a more effective contact with uneven surfaces and give clearance should the fixing screw head be slightly proud of the countersunk hole. […]

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Agreed

But here is why I was less-than-impressed by the ‘technical’ details in the Eclipse document

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MichaelG.

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Edit: __ There is presumably an unmentioned distinction between ‘potted’ and ‘in a pot’

Edited By Michael Gilligan on 20/12/2022 11:38:27

[peak4Participant @peak4]

Posted by Michael Gilligan on 20/12/2022 11:25:34:

Posted by Martin W on 20/12/2022 11:14:14:

Michael

I don't think that this magnet is a potted variety. The magnetic material has been formed with a stepped rim to allow it to make a more effective contact with uneven surfaces and give clearance should the fixing screw head be slightly proud of the countersunk hole. […]

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Agreed

MichaelG.

Well, they are described as a "Shallow Pot" (with countersunk hole) on P 19 of the Eclipse catalogue, so I hope that's what you receive.
P17 lists plain "Neodymium Rings" (with a countersunk hole), which I assume to be the plain unpotted ones.I have some of the latter from a different source, but have found the holes to be a bit too shallow for most countersunk screws.
It looks to me as though the coloured pots at the foot of P19 are just as described; i.e. coloured pots containing a zinc plated countersunk button magnet.

Michael;
Looks like we were typing at the same time, your post wasn't there when I started typing mine, but i got disturbed by a coffee part way through.

Bill

Edited By peak4 on 20/12/2022 11:46:02

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, although mine is an earlier version of an Eclipse shallow pot magnet, which is a 828C in the Table of Dimensions below, it is of much the same design and has a keeper disc for when it isn't in use, and there is a photo, No.19, of one attached to a glove and some in photo 21, attached to the underside of a shelf for holding cooking pot lids, also below. The magnet is only slightly below the pot by a few thou, maybe about five at the most.

Regards Nick.

[Martin WParticipant @martinw]

Perhaps their understanding of the words are:

Pot; – Referring to shape of the base material.

Potted: – Being contained within an enclosure or part enclosure.

This seems logical to me but still could cause confusion if read in isolation

Martin

[Michael GilliganParticipant @michaelgilligan61133]

Indeed, Martin … and I would take the distinction a little further; in that this [on p25] is what I would consider ‘potted’ in the sense of being embedded in resin:

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The problem I have with Eclipse is that they don’t appear to explicitly tell us what they mean.

[ memories of Humpty Dumpty ]

MichaelG.

[peak4Participant @peak4]

Posted by Michael Gilligan on 20/12/2022 18:26:00:

Indeed, Martin … and I would take the distinction a little further; in that this [on p25] is what I would consider ‘potted’ in the sense of being embedded in resin:

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The problem I have with Eclipse is that they don’t appear to explicitly tell us what they mean.

[ memories of Humpty Dumpty ]

MichaelG.

As I read this, the difference is that this type above is described as BiPole pot; note that it is a brass case which won't form part of the magnetic circuit.; it's a button magnet in a brass pot, rather than a disc magnet in a steel/iron pot.
Half of the front face will be North, with the other half South poles, just like a button or horseshoe magnet.

This means that in one position, two magnets will be strongly attracted to each other, whereas if you twist one by 180° along the axis, they will repel each other. You could maybe use them for holding a door closed, but force it open when the handle is rotated 180°, (as well as its conventional use against a steel plate etc.)

I suspect potted magnets with an iron/steel pot have south in the centre, with north concentrically in the outer of the pot.
i.e. they are conventional disk magnets with the pot to complete the circuit and bring both poles to the front, but concentrically.

It could of course be the opposite polarity, depending on the maker/purpose.

I've just been out for a quick play in the workshop.
My countersunk, non-potted magnets have the south pole on the countersunk side, as evidenced by deflection of a conventional magnetic compass; this is just like a disc magnet

A magnetic car aerial base is effectively a larger potted magnet, with an air rather than resin/brass gap, which in the case of the two I tried had South in the middle, and North concentrically around the outside in the steel casing.

It's not helped that many sellers on eBay etc describe their disc/flat magnets, featuring one pole each side/end, as "Button" magnets, which should really present both poles on one face. (as per Page 11)

Addendum
After another workshop trip, this time with a small cylindrical magnet and an ex computer hard drive magnet.
The cylindrical one is really just like a very thick disc magnet, north pole on one flat end, south on the other.
The HDD magnet, whilst thin and flat is quite different to a round disk magnet.
It's a thin kidney shape, but in this case one lobe of the kidney is north and the other south, so not aligned front to back, but end to end.

Mind your fingers if you're playing with these, they bite particularly if you have a pair.
I was holding a small cylindrical magnet against the kidney shaped HDD one looking for attraction/repulsion, but the steel pliers were quite strongly attracted to the bigger magnet.
That attraction was greater than the much smaller cylinder, such that when I released my grip on the pliers a bit, the little one shot out of the jaws, and across the full length of the garage; still not found it yet.

Bill

Edited By peak4 on 20/12/2022 20:54:54

[Nicholas FarrParticipant @nicholasfarr14254]

Hi MichaelG, some disc magnets do have the north pole on half of the disc and the south pole on the other half, rather than the opposite faces. The disc magnet that I used in the compass I made Magnetic Compass has the poles split across it rather than the opposite faces.

If one end of a bar magnet is presented to the tail end of the pointer in the photo above, this being the active part in my compass, it will either stay where it is or it will rotate it so that the point is attracted to the bar magnet, reversing the bar magnet end for end will make the pointer turn the other way, the pointer itself is made of aluminium and is just glued to the magnet. This magnet was one of three from trimmers in association with the coils on the neck of a colour TV tube. There are no magnetic metals in my compass that would influence the rotation of the magnet.

Regards Nick.

[Michael GilliganParticipant @michaelgilligan61133]

For your continuing amusement, Bill … see if you can decipher the description of that Brass-cased one, here:

**LINK**

https://www.zoro.co.uk/shop/hand-tools/magnets/neodymium-pot-magnets/f/33650?brand=Eclipse%20Magnetics

MichaelG.

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P.S. __ I need to get an early night … B12 booster jab tomorrow morning.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Nicholas Farr on 20/12/2022 22:32:37:

Hi MichaelG, some disc magnets do have the north pole on half of the disc and the south pole on the other half, rather than the opposite faces. […]

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Thanks, Nick … yes, I know that, but it’s interesting to see your compass

MichaelG.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi MichaelG, apologies if I've misunderstood what your knowledge about disc magnets is. Thanks for finding my compass interesting.

Regards Nick.

[Michael GilliganParticipant @michaelgilligan61133]

No need for apology, Nick

… if anyone needs to apologise, it’s me [for being brusque]

Dashing off for my B12 jab now … back later

MichaelG.

[Anonymous]

Posted by Michael Gilligan on 21/12/2022 08:36:25:

Dashing off for my B12 jab now … back later

Lucky you … arm or stomach?

[Neil WyattModerator @neilwyatt]

Posted by Martin W on 20/12/2022 17:19:55:

Perhaps their understanding of the words are:

Pot; – Referring to shape of the base material.

Potted: – Being contained within an enclosure or part enclosure.

This seems logical to me but still could cause confusion if read in isolation

Martin

No… pot magnets are the ones used for storing saucepans…

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Peter Greene 🇨🇦 on 21/12/2022 18:21:38:

Posted by Michael Gilligan on 21/12/2022 08:36:25:

Dashing off for my B12 jab now … back later

Lucky you … arm or stomach?

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Top of left arm … thankfully

My ‘Tigger Bounce’ should be restored for a while

… next one is scheduled for the Ides of March [by which time, I will likely be fading again]

Meanwhile: The magnets have not yet arrived.

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Don’t hold your breath, chaps … message from ebay this morning informs me that my item “is being posted” today, and I should expect it by 04-Jan-2023

MichaelG.

[Ian ParkinParticipant @ianparkin39383]

Michael

i ordered some from zoro and had the email this morning saying its being posted and surprise Parcelforce has just turned up with the magnets

[Ian ParkinParticipant @ianparkin39383]

[Ian ParkinParticipant @ianparkin39383]

3 boxes of 10 arrived in a much oversized plastic bag

each magnet has a nylon washer between it and the keeper

[Michael GilliganParticipant @michaelgilligan61133]

Thanks for the info, Ian

… looks promising.

MichaelG.

[Neil WyattModerator @neilwyatt]

Posted by Michael Gilligan on 21/12/2022 18:56:05:

Posted by Peter Greene 🇨🇦 on 21/12/2022 18:21:38:

Posted by Michael Gilligan on 21/12/2022 08:36:25:

Dashing off for my B12 jab now … back later

Lucky you … arm or stomach?

.

Top of left arm … thankfully

My ‘Tigger Bounce’ should be restored for a while

… next one is scheduled for the Ides of March [by which time, I will likely be fading again]

Meanwhile: The magnets have not yet arrived.

MichaelG.

They do marvels for my dad. He missed them for over two years due to covid restrictions, but when he finally got a 'top up course' it worked wonders.

There's always intravenous Marmite as an option…

Neil

[Anonymous]

Posted by Neil Wyatt on 22/12/2022 11:34:48:

Posted by Michael Gilligan on 21/12/2022 18:56:05:

Posted by Peter Greene 🇨🇦 on 21/12/2022 18:21:38:

Posted by Michael Gilligan on 21/12/2022 08:36:25:

Dashing off for my B12 jab now … back later

Lucky you … arm or stomach?

They do marvels for my dad. He missed them for over two years due to covid restrictions, but when he finally got a 'top up course' it worked wonders.

Some years ago, I had B12 injections along with some other injection (don't recall what, except it was nominally very expensive but the health service picked up the tab) – in the stomach …. actually no worse than in the arm.

When various blood levels stabilised a bit, I was taken off those injections and switched to Revlamid (Thalidomide) instead (really, really expensive … ~$10,000 a month and highly controlled for obvious reasons).

Just a week ago, the Oncologist asked me if I was "still" taking the B12 tablets because some levels looked a bit iffy. "No" I said "no one ever said I should". I am now.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Michael Gilligan on 22/12/2022 11:24:07:

Thanks for the info, Ian

… looks promising.

MichaelG.

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Mine arrived today … in a small ziplock bag in the enormous mailer

Three magnets but only two nylon washers and keepers

They are much better finished than I expected, and it is now evident that the magnet is only perhaps 0.2mm below the rim of the pot … the appearance is deceptive, because the magnet does not sit concentric in the pot [the gap is zero at one location]

Pushing them around [all the same way up] on a melamine-faced board, they settle at about 40mm centres, and rotation has no effect.

With the rim down, they will just jump about 4mm to contact a steel plate

With the rim up, this increases to a much more dramatic leap of about 20mm

They don’t initially give the impression of being very strong … until they attach to a flat surface … and then it’s like a limpet !!

… I will try a weight-lifting test tomorrow

So far, I am quite impressed.

MichaelG.

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Note: All my ‘measurements’ are approximate … I’m just faffing about with them

Edited By Michael Gilligan on 23/12/2022 21:45:54

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