How do I demagnetise tools and parts of machines

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How do I demagnetise tools and parts of machines

This topic has 12 replies, 9 voices, and was last updated 11 May 2010 at 20:39 by David Williams 6.

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7 May 2010 at 13:46 #51486
David Williams 6
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@davidwilliams6
A number of my engineering tools and parts of my machines have become magnetic. I bought the small demagneising box with the two holes but it is ineffective and anyway it cannot be used on the motor housing of my small Chester Mill etc. Would someone be kind enough to show me where I am going wrong with the small demagnetiser and if possible suggest a solution to bigger items. I am aware of the degaussing of ships to protect against magnetic mines, are there machines for this(?) as I cannot simple bash the motor housing with a large hammer or for that matter my engineering tools…… Any help gratefully received.
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7 May 2010 at 13:46 #5055
David Williams 6
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@davidwilliams6
7 May 2010 at 14:52 #51487
dcosta
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@dcosta
Hello David.

I’m Writing from Portugal.

A while ago I bought (I think from RDGTools) a demagnetizing table made by Vertex and with it I could demagnetize all the tools which were magnetized and even my precision

toolmaker’s vice was demagnetized. It was enough to slide the table on the vice or, as was the case with my twist drills, to slide them on the surface of the demagnetize. Before

writing this message I looked for the demagnetiser in the RDGTools site.

I can only say I’m happy with it.

Best regards

Dias Costa
7 May 2010 at 15:00 #51488
Ian S C
Participant
@iansc
As far as your mill goes I imagine that it has a DC motor and electronic speed control, it’s supposed to be magnetised. For small tools I built a demagnetizer. The coil is the primary coil from the HT transformer of a microwave oven, it is fed with AC current from a transfomer at about 12V (a little more or less won’t hurt just as long as it can be left on for a few minutes without getting too hot), I built a box around it leaving a hole about 2″x 2 1/2″ through which the object being demagnetized is passed, you have to move the object away from the magnetic field before switching off. In my early days in aircraft engineering we had a bigger version of this (ex RNZAF), we used it for magntizing steel parts for crack testing, then demagnetizing after the test was completed, the system seemed crude but it worked, and the powers that be thought it was OK. Someone else will have something more practical I’m sure. Ian S C
7 May 2010 at 18:25 #51495
Pierre EHLY
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@pierreehly19171
Hi David,

For tools demagnetisation use an magnetic field generated by an AC current.

Use the stator (fixed part) of an old AC (240Vac) motor. Connect a light bulb

(40 to 75w) in serie with the field winding an power it up with 240v.

Pass slowly the tool in the stator, thats all.

IMPORTANT:

Isolate all connections (240v may be lethal) & connect all metallics part to ground

Watch also the T° rise of the stator

For machine part , built a fixture to move the stator over the affected zone

2 or 3 time (distance varie with the power )

Select a bulb that give you the half of the normal motor current

pm
7 May 2010 at 20:54 #51499
Sub Mandrel
Participant
@submandrel
My Dad used to have a degaussing coil for TV tubes – It was about 10″ diameter on (IIRC) a tufnol frame and you demagnetised a tube by pressing a button on the (mains) coil and waving it around the tube then walking slowly away to, I think, about 10′ distance. I don’t know how many turns the coil had, but I can imagine it would work well for fair sized tools. Note it didn’t have a steel core – the steel core on a transformer traps the magnetic field. I’m sure demagnetising tables must have steel cores, but with open poles at the demagnetising areas.

When I had a blue spot on an old CUB computer monitor some ten years ago, I managed to demagnatise it by waving a ceramic speaker magnet at it – but it took a few goes! Not sure THAT would work for tools

Neil
7 May 2010 at 22:38 #51505
Steve Garnett
Participant
@stevegarnett62550
Following on from what Neil said, years ago I made a cheap, flat
demagnetiser like the Vertex one out of an old mains transformer, and I
can tell you what you need to do to get over the trapped field problem.
What you have to do is to knock out all of the E and I laminations,
which are normally interleaved, and put all the E ones back facing in
the same direction. This will give you two pole faces available, and
that’s essentially what you need to pass whatever you need to
demagnetise over.

As with Pierre’s motor
arrangement, a light bulb in series with the primary, which is still
mains-connected is a good idea, otherwise the whole thing will overheat
rather quickly. But for not too much effort, you can get a workable
result and it’s a damn sight cheaper than the Vertex one is. If you make
one, it’s generally a good idea to use a spring-loaded switch biased to
the off position, so that you have to hold it on to use it. That way,
it doesn’t get left on accidentally.
8 May 2010 at 08:51 #51506
john fletcher 1
Participant
@johnfletcher1
De-magetising.

I have a home made growler, which I use for simple testing of armatures,and for de-magnetising, growlers were found in most auto electrical shops in the days of dynamos. To make the growler I used a mains transformer 240/55 about 10amp rating with the secondary (55volts) coil removed,the core is best described as square 8 shape. I bound up the remaining coil to ensure no steel particles could get in whilst I milled away a vee in the top portion of the 8 shape, deep enough to lay an armature in. To de-magentise a piece of metal all I do is switch on and pass the tool,metal or what ever through or across the vee. My growler doesn’t over heat and it can be used to remagnetise small DC motors, like those found in childrens train set. Observing polarity place the complete motor in the vee connect the coil to a source of DC, switch on for a moment and the motor is like new. Alternativelydischarge a large capacitor across the coil and that has the same effect.Ted
8 May 2010 at 14:05 #51510
Geoff Theasby
Participant
@geofftheasby
I used to have a tape head demagnetiser for my reel-to-reel tape recorder. They may still be available.

It was a coil wound on a steel core and plugged in to the mains. The core was extended into a probe covered in plastic which was touched onto the tape head and then withdrawn to a few feet before being switched off.

I used it to demagnetise screwdrivers and other tools.

You can demagnetise screwdrivers and other small tools by stroking them with a small permanent magnet.

Regards

Geoff

Edited By Geoff Theasby on 08/05/2010 14:07:43
8 May 2010 at 15:50 #51511
V8Eng
Participant
@v8eng
I keep a couple of screwdrivers magnetised. They will hold small steel screws in line when working in difficult locations.

Certainly beats dropping the things.
9 May 2010 at 01:41 #51521
Ian S C
Participant
@iansc
Hi V8Eng,magnetised screw drivers are also handy for getting swarf out of difficult places on the mill and lathe.Ian S C
9 May 2010 at 16:10 #51545
V8Eng
Participant
@v8eng
Edited By V8Eng on 09/05/2010 16:16:14

Edited By V8Eng on 09/05/2010 16:17:07
11 May 2010 at 20:39 #51629
David Williams 6
Participant
@davidwilliams6
Dear All, May I say a really BIG THANKS to everyone who has been so believably helpful and I am now considering what to do next. I think that with all the options and help that has been posted, then unless anyone has anything really special/useful to add, I will call it a day and suggest we informally close the thread line. As I am sure you all realised, I really meant the motor fixings or vices or tables etc. rather than the actual motor itself. Not the best of examples to suggest – anyway it probably gave you a laugh. Many thanks again, David
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