Magnetised digital calipers

I have a rather nice TESA IP65 digital calipers that lives in the workshop. Its body is a magnetic stainless steel and is slowly becoming magnetised. Wiping steel dust off it has become a pain.

I have a good demagnetiser. If I used it on the calipers will I destroy the electronics?

JA

Not to my knowledge I demag my mitutoyo fairly regularly

You can also try duct tape, it gets tiny chips off even strong magnets quite effectively.

You could try one of the little wands used to degauss the heads in cassette recorders.

BluTac provides a consumable method of removing swarf.

But passing through a weak AC field should do the trick.

A passive method, but probably slow, would be store the calliper on an East West meridian, so that the magnetism gradually decays.

Howard

Demagnetising requires a decaying AC flux initially larger than the remanent flux in the job, a weak field may not do anything. I'm not sure why storing it on an EW meridian would do anything at all, it probably got magnetised either from magnetic tools or being in the field of a motor.

John,

Storing a ferrous object on a North - South meridian will eventually magnetise it, so an East - West should reverse the process, but not not necessarily quickly. The same applies if hammered on those axes, but not recommended for a measuring instrument!

As you say, the secret is a decaying AC magnetic field. Passing the callipers through a coil carrying AC will provide the decaying flux as the calliper enters and leaves a field the strength of which decreases according to the inverse square law. So as the object recedes from the coil, the field deceases rapidly.

We used to demagnetise crankshafts after crack detection, by pushing them along a roller track, through a coil connected to the AC mains.

Howard

I don't really see why that should follow,Howard. I would have thought that E-W would simply do nothing.

If anything storing it N-S with field reversed might do something but admittedly outside my pay grade

My memory about magnetism was that you demagnetised an object using an alternating and weakening magnetic field as John stated. You could magnetise an object by using a no-alternating magnetic field, by holding the object, a steel rod say, north-south at an angle of 70 degrees, in the UK, to the Earth's surface and hammering it or by wiping it with another magnet. I think things become magnetised in the workshop by the last mechanism.

My worry is what would a strong alternating magnetic field do to the electronics of the calipers. If I had a cheap digital calipers I would do as Bernard suggests as a trial but I don't.

Perhaps I should put the whole workshop through such an alternating magnetic field.

JA

I saw a quick tip somewhere for making a de mag tool using piece of wood,plastic or anything to hand about 40 dia with a shaft through it into which embed 4 Neodymium Magnets two with north facing out two with south facing out and alternating. Pop it in the drill press and turn on offer whatever you want to de mag just under the rotating magnets then slowly move away, so when I do my caliper I just offer the jaws under then as I previously said just slowly move away.

H

I had the same issue with a cheap caliper. It was a pain to clean so I decided to de-magnetise it. I thought if it works great, if not then I will get a new one. That was two years ago and it is still working fine.

John.

Curiously, I just bought a magnetiser / demagnetiser from Aldi for £2.99 (I mean, why not?).

It has 2 holes and you pull a screwdriver through one to magnetise it and the other to demagnetise it.

It *seems* to work - at least on an old phillips screwdriver. I've no idea how.

It won't do for calipers mind you - the hole's too small.

Iain

I managed to magnetise my Mitutoyo digital calipers by (clearly without thinking first!) using them to measure a neodymium magnet!

I demagnetised them on my Eclipse demagentiser after first taking the battery out (not sure if that's necessary, but figured it couldn't hurt...) and they've been fine ever since.

Jez.

I bought one of those things, not from Aldi and costing more than £3. I found it very good at magnetising things but useless at demagnetising.

JA

JA I got the same result with one from Aldi 

Edited By roy entwistle on 26/07/2020 14:14:32

This afternoon I took a good look at the calipers and found that the reader (the electronics) could easily be detached from the two slides. So I unscrewed the screws, removed the reader, demagnetised the slides and then reassembled everything. And it works.

JA