Magnetic bases – stored on or off?

[Pete RimmerParticipant @peterimmer30576]

Several times I have posted a copy of the Eclipse handbook for magnetic chucks that says if you dismantle the chuck it will lose magnetic effort and require re-magnetising to restore it.

[Neil LickfoldParticipant @neillickfold44316]

With the eclipse magnetic chucks, when you take them apart, place a metal strap that covers all of the assembly on both side of the Bars. This will retain the magnetism of the assembly until you reassemble it again. It needs to have the plates applied as soon as possible. Not  hours later.

Neil

[Pete RimmerParticipant @peterimmer30576]

If anyone wants to read the very informative handbook on Eclipse magnetic chucks you can download the manual from my dropbox. The manual will tell you what type of magnets are used in their chucks, how to care for the chuck, how to grind the chuck, whether you can open them up without losing magnetism (you can’t, even momentarily according to Eclipse) and it even goes into detail as to why you can or cannot do these things.

If you own an Eclipse chuck, do yourself a favour and download the handbook from the link below and read it before attempting service or disassembly:

Eclipse permanent magnet chuck users handbook

 

[Michael GilliganParticipant @michaelgilligan61133]

Very noble of you, Pete

MichaelG.

[Steviegtr]

On Steviegtr Said:

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.

Steve’s post deserves more attention!  This type of magnetic base does not have a keeper, and I believe it’s the most common.   Unfortunately, I can’t prove it by taking mine apart – can’t see any screws, and suspect it’s a press-fit assembly.  I don’t want to break it.

HSMag’s description appears to be a shortened version of that on wonkydonkeytools, which has more diagrams.  This pair I think shows more clearly how moving the magnet magnetises the base, there is no keeper:

 

 

The absence of a keeper is counter to what I was taught at school, but in later life I found many examples of lessons that were too simplified, or out-of-date.

Early magnets weren’t made of the best possible materials because they hadn’t been discovered yet, and permanent magnets demagnetised.  Their decay was slowed by completing the magnetic circuit with a keeper.

Poor magnetic materials caused a lot of problems, such as failing magnetos,  so materials scientists have been looking for improvements for over a 150 years.  Very successfully, first with a basic AlNiCo, then a series of improvements, ending with today’s Rare Earth alloys.   Modern materials demagnetise very slowly, so the need for a keeper has diminished, perhaps to vanishing point.  However, the need for a keeper is embedded in folk-lore and it’s “not wrong”.

I don’t think there’s a black and white answer.  There’s a good reason for putting keepers on ancient magnet bases, and good reasons turning modern bases off, even though that means there’s no keeper.   It depends on what the magnet is made of and what the designer allowed for.

Moving on, I can’t find the internet explanation of why Eclipse magnetic gizmos self-destruct when opened.  However, if I remember correctly, grinding clamps are carefully engineered to maximise the magnet flux available for clamping.  Unfortunately, a side-effect is opening the box causes the magnet to demagnetise itself.  In this diagram, imagine the flux shown turning back on itself at the poles being strong enough to permanently wrench billions of atomic N-S alignments inside the magnet sideways, thus weakening it.   Rapidly apparently!

I expect the magnet self-destructs when opened by Eclipse, but they have the wherewithal to re-magnetise it.  We don’t!

It’s possible Eclipse changed what the magnet is made of.  An original AlNiCo magnet would demagnetise, whilst a rare earth substitute might not care.

Dave

 

[DiogenesParticipant @diogenes]

Re. “This type of magnetic base does not have a keeper” …

..this is what it looks like in the off position..

 

 

[john fletcher 1Participant @johnfletcher1]

If the magnetic base has lost its magnetism, how about contacting a magneto re magnetiser, their services are advertised in Motor Cycle Magazines such as Old Bike Mart. Not sure of the latest cost though. It used to be a quick job, On / Off.  John

[jamesp1Participant @jamesp1]

There is a keeper built in to rotary-switched magnetic bases. So you can leave them switched off in a box with no keeper, or standing on a piece of steel or iron switched on. Below diagram makes it a bit clearer how that works.

The push button ones work similarly, but axially rather than radially. The magnet is bobbin shaped. North and South poles are respectively each raised end of the bobbin. The brass separator plate is rotated 90 degrees to match. When you push the button so the two poles are either side of the off-centre brass separator, the magnet is “on”.  Push the button the other way to “Off” and both poles are on the same side of the brass separator, so the iron body acts as a keeper. Thus, like the rotary type, it can be stored switched “Off” , or stored stood on a steel plate and switched “On”.

 

 

[Michael GilliganParticipant @michaelgilligan61133]

Rather strangely … Google fails to find much about “remagnetizer” although this one is TradeMarked as such:

https://allmagnetics.com/education/magnetizer.htm

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

< deleted double post >

[Diogenes]

On Diogenes Said:

Re. “This type of magnetic base does not have a keeper” …

..this is what it looks like in the off position..

 

 

This cleary shows that there are TWO kepers, one each side. The null point is across the diameter of the cylindrical magnet. So in the off position it is shunted by the pole pieces on each side.

Robert.

[Michael Gilligan]

On Michael Gilligan Said:

Rather strangely … Google fails to find much about “remagnetizer” although this one is TradeMarked as such:

https://allmagnetics.com/education/magnetizer.htm

MichaelG.

That is because the web is saturated with ads for small screwdriver magnetisers based on permanent magnets.

Professionally most magnets are magnetised using a capacitive discharge unit like these:

https://www.magnetic-instrument.com/magnetizer-5.htm

Note the very high currents that enable high ampere-turns and thus field strengths.

I’ve used a smaller version with a switched capacitor bank and variable voltage to adjust the strength of magnets in various aircraft instruments. For example remote tachometer systems. These have two magnets that may need adjustment. The tachogenerator magnet is adjusted to get correct output voltage. The indicators are a drag cup design and their magnets need adjustment if the depth adjustment runs out of range.
You need a magnetising coil with pole pieces machined to match the poles of the instrument magnet. In production they pretty much know the setting to use. When adjusting an instrument that you may only do rarely it’s very much a matter of judgement, luck and repeated tries…

Robert.

[Robert Atkinson 2]

On Robert Atkinson 2 Said:

.. …This cleary shows that there are TWO kepers, one each side.. ..

👍

[Bernard WrightParticipant @bernardwright25932]

I’ve got 5 heavy duty Eclipse mag stands that live on the milling table, always on (the push button type).

Must have had them 35 years now, no apparent loss of grip, always need a good sideways yank to release them.

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