De-Magnatizing digital callipers

Hi all,

The jaws on my digital calipers have become Magnetic and they now pick up swarf that is annoying the heck out of me , Has anyone got a solution other than pegging them in the bin?

I was thinking of trying one of those De- Magnatizing tools used on screwdrivers.

Not sure if this has been asked before but I have such little confidence in searching the forum that I just can't bring myself to do it !

Ian.

Hi Ian,
Have a look at these two threads.

Demagnetiser
How do I demagnetise tools and parts of machines

I use a coil removed from a stepper motor that was removed from an old printer (Dec LA36) I feed this with 24 volts AC. To use a similar coil apply the power to the coil WHILE IT IS SOME DISTANCE FROM THE ITEM YOU WISH TO DEMAGNETISE move it close to the object and pass it all over the surface. (Pass the object through the coil if it will fit.) Move the coil slowly away from the object. ONLY WHEN IT IS SOME DISTANCE FROM THE OBJECT switch the power off.

Les.

Edited By Les Jones 1 on 03/07/2013 21:04:38

Certainly dont throw then away (if you meant that seriously) just make yourself a demagnetiser.

Mine is an old CH circulating pump, its the type with a flat thin SS sheet between the stator/windings etc and the rotor which is integral with the impellor. You just want the stator half and the copper rotor goes in the scrap bin.

Fit a suitable fuse, on/off switch, cable etc. Switch on before introducing parts to be treated then move them around a bit in the magnetic field before slowly withdrawing them, then switch off. Dont leave it powered up for too long as the windings overheat and unpleasant aromas abound before there is an escape of smoke.

Ian P

If you have one of those Weller instant soldering guns, pulling the trigger and sticking a magnetised object through the hairpin shaped element, then withdrawing it slowly and getting it a few inches away before releasing the trigger will demagnetise it. Caution - the element gets hot, so watch your fingers and the plastic bits of the caliper.

If you are happy working with mains electricity and have an old transformer, you can make a better demagnetiser, as in this LINK. Mine has 10W ceramic resistors (heatsinked) rather than a capacitor, in series with the 230V primary winding to limit the current. The low voltage secondary winding is still there, but disconnected. Again, the object needs to be passed slowly through the field (you will feel it vibrate) and away before switching off the current.

Andy

Hi I wonder what effect demagnetiser's may have on the elctronics in the caliper --if any? Anyone know the answer?

No effect on any of my calipers, John. They are all just as almost, but not quite, accurate as they were before treatment (most of them came from Aldi/Lidl, so have never quite agreed each other, or with my M&W mics).

If you can build a degausser, it really is a great help with HSS tooling, screwdrivers etc which have been turning into furry monsters when they get near swarf.

Andy.

Digital calipers are hardened stainless steel

It really shouldn't be possible to magnetise them

Any chance you can tell us how you managed to magnetise stainless steel?

Edited By Ady1 on 04/07/2013 00:45:13

Must be some different properties

http://en.wikipedia.org/wiki/Stainless_steel#Properties

(Even when I try to magnetise my calipers I get no luck)

Edited By Ady1 on 04/07/2013 01:12:02

Big myth: .... stainless steel is nonmagnetic ..... some alloys are, some aren't.

Ady1.. cut from Wikipedia:

Ferritic and Martensitic stainless steels are magnetic.

Austenitic stainless steels are non-magnetic.

Thanks all for the speedy replies and links .

I like the idea of using an old AC transformer then modifying the laminations and you get some usefull packers for the lathe as a by product !

I'm not sure if a degaussing wand for a tv would also work but they are only $40 and to build one from scratch would cost more unless one had the right parts in the junk box - i have everything here to make one .

Andy,
What sort of current have you limited the primary coil to ?
I have an old 230v/12v @ 1amp transformer and under load it draws about 150ma on the primary so i suppose if i stick close to this it would be ok.

Imagine the unit one could make from an old stick welder !

I'm not sure how they became magnetised all i know is it makes them unusable !

Ian

The tool magnetisation is with me an, On/ Off effect. I will be working away happily and then suddenly I pick up a tool and its all festooned with bits of swarf! I give it quick bang on something solid and it is OK again though I dont bang the calipers. It seems its a quite random effect being there one day but not the next. It only happens on the machines and not on the bench tools. Away from the Lathe and Mill the tools do not show the magnetism at all.

I wonder if a real earthing spike might help with a cable from all the machines taken to a copper spike in some damp soil. Is it static electricity doing it or actual contact magnetism? It is only recently that this has started to happen and have not come across it at work over the years.

Clive

Clive

I doubt the earthing spike would help, also static wont be the cause of your magnetised tools.

Did you fit a new machine or move some electric equipment at the same time as you started to see the problem? The switch on and switch off surge is probably the cause. To magnetise something it needs to be very close to some device generating the magnetic field (probably a motor). The effect is strongest (and probably the only place) is very close to the motor casing.

Ian P

Hello Ian, No, I have not fitted or moved anything and as I said it is just an intermittant problem and affects the Verniers and the spanners and the lathe tools periodically. It also happens half way through a job and suddenly all the tools on the Mill will have shards of metal sticking to them.

The Mill motor is DC so there is a strong field near it but I certainly dont wave tools around it. It just starts on the Mill table and on the Lathe it appears on the wooden tool tray just in front of the bed!

The next day there is no magnetic effect, very strange and puzzling indeed.

Clive

HI Ian,
I would suggest something larger than a 12 VA transformer. I would think you could get away with limiting the current to about twice the original design current as it will only be switched on for a few seconds at a time. (More current means stronger magnetic field.) One other source for an old transformer would be from a scrap microwave oven. IF YOU USE ONE OF THESE REMOVE THE SECONDRY WINDING BEFORE APPLYING POWER TO THE TRANSFORMER.

Les.

Edited By Les Jones 1 on 04/07/2013 08:34:14

Well that is weird, presumably you have ruled out a practical joker!

It point to a random magnetising pulse but I cannot imagine what could produce enough effect without being close to the spanners etc.

What you need is a magnetic anomoly detector, something like a compass that rings a bell if it gets a sudden deflection so you dont have to watch it all the time. Come to think of it why not just place a compass in different places and see what it does when you switch things on and off.

The point of the AC cycle that the contact actually makes or breaks affects the surge so you need to repeat the test a few times.

Ian P

I've got to do a week's worth of tidying up this morning, Ian, 'cos my cleaner is due and I pay her to clean, not to clear up the debris I leave lying around. I'll put the old Avo on it later and let you know. I recall that on full mains voltage, it heated up once the E laminations were all pointing the same way. I experimented with incandescent lamp bulbs of various wattage in series until it calmed down, using an ammeter to measure the current when the lamp was dimly lit., and then substituted ceramic resistors .

The chap on my earlier MadModder link stuck a piece of iron (probably cast iron so it wouldn't magnetise permanently) across the ends of his laminations, but I didn't bother and simply arranged things so they almost touched the underside of the earthed aluminium box which stops the electricity falling out.

I think one way of making a magnet is to hammer steel so that (in crude terms) its internal structure tends to arrange itself north-south along the Earth's field. Maybe the bumpy ride encountered in use by HSS tools might have the same effect? Again in crude terms, the 50Hz alternating field of a demagnetiser disarranges the structure, but as already said the item has to be moved reasonably slowly away.

I don't know how my screwdrivers and calipers get infected, though.

I wonder if you could get the same effect with a row of neobdymium magnets, and drawing the object along the row and slowly away, thus taking it through an alternating field.

Andy

Jason

I'm not sure the difference between para' and dia'magnetic is a simple as that, not that it makes any difference to Ian or Clive's problem.

Swarf made from ferrous metal will stick to a magnet, regardless. Its not likely that each bit of swarf will have a north and south pole, if it did it would just orientate itself on its way to the magnet.

Ian P

Edited By Ian Phillips on 04/07/2013 09:56:21

Interesting, was just yesterday musing about "self magnetization ? " I have bits all over 2 different sheds which sometimes are heavily covered with swarf and dust, sometimes clean. Sometimes disapears at random. Have never tried to demagnetize as usually gone next time. Hammering iron in the earths magnetic field used to be a way to make magnets, the most usual things to become magnetic, and lose it, are center punches and chisels. The odd thing is I've never noticed this effect in the house bit. My non tech theory is that it's got to do with the orientation of the item in the natural magnetic field.

In the second site indicated by Les I describe how I made my demagnetizer, using the primary coil (you could use the secondary) from a micro wave oven transformer. The power source is the transformer for a low voltage electric blanket, it has three voltages 6V 9V 12V, the low voltage is quite adiquate.

Ian S C