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Author Topic: Tweakie's De-Mag.  (Read 3653 times)

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Offline Tweakie.CNC

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Tweakie's De-Mag.
« on: May 27, 2012, 06:32:48 AM »
Another little project for a rainy day.

After trying one of Art’s ideas of wooden clock gearing using small magnets instead of teeth I encountered a problem. First, one of my small screwdrivers became magnetic then it spread, like a virus, to most of my other small bench tools and having used some steel wool (on a previous occasion) almost all my tools were picking up minute, unwanted steel whiskers.
Having seen a de-magnetizer project on eHow I set about making one and this is how I did it.

Taking an old, unwanted, mains power unit (from a long gone printer) I removed the transformer. The Mu laminations were carefully removed, the ‘I’ sections discarded (well some have been kept as lathe tool packing pieces) and the ‘E’ sections replaced, all in the same direction. The first ‘E’ is the hardest to remove but don’t worry if it is damaged or bent because on replacement they all fit back, except one, so the damaged one can be discarded.
It is only the mains, primary, winding that is used so the secondary windings are just left open circuit.
I fitted a small piece of iron onto the centre pole using epoxy then cut an appropriate sized hole in a project box and glued in the transformer again using epoxy.

When the transformer laminations layout is altered in this way, the whole flux pattern is changed and as a result it is necessary to limit the current flowing through the winding. This is best achieved by using a mains rated capacitor, connected in series (the larger the capacitance value the larger the current and visa versa). The original mains lead was re-used and the de-magnetizer was tested - it works just beautifully and removed all the residual magnetism from my small bench tools in just seconds.

The capacitor I used was a 2uF 400Volts starter capacitor and this is connected in series with the coil. Incidentally if the capacitor used does not already contain a shunt resistor then a 1 Megohm 5W resistor should be fitted across the capacitor to discharge it once power is disconnected.

Tweakie.
« Last Edit: May 27, 2012, 06:35:43 AM by Tweakie.CNC »
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline RICH

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Re: Tweakie's De-Mag.
« Reply #1 on: May 27, 2012, 07:10:10 AM »
Any insight on what to do if the mill table is becoming magnetized.
Interestingly a friend mentioned that after milling a lot of hardened material using a carbide fly cutter his table, vise etc has become magnetized.
I have seen this happen with the chips, but never the whole table.

Any thoughts on the matter??

RICH

Offline Tweakie.CNC

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Re: Tweakie's De-Mag.
« Reply #2 on: May 27, 2012, 08:41:44 AM »
Hi Rich,

In general de-magnetizers are something that are used infrequently but many machine shops have professional models (Eclipse) for de-mag'ing their cutters - I think these would work quite well, inverted and slid across the top of a machine table, and perhaps one could be borrowed or hired for the purpose.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline N4NV

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Re: Tweakie's De-Mag.
« Reply #3 on: May 27, 2012, 10:50:06 PM »
I have seen an entire airplane airframe demagnetized.  They wrapped a wire around the plane, about 50 turns for the length of the plane (a Mooney, a single engine small plane).  They then hooked the wire to a variable AC transformer with a resistor in line to limit the current and ran an AC current through the wire for about 5 minutes.  I imagine you could do the same thing for a mill table.

Vince

Offline Sam

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Re: Tweakie's De-Mag.
« Reply #4 on: May 27, 2012, 11:17:01 PM »
That's pretty nifty, Tweaks. The ideas never stop for you, do they. :)
"CONFIDENCE: it's the feeling you experience before you fully understand the situation."

Offline budman68

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Re: Tweakie's De-Mag.
« Reply #5 on: May 29, 2012, 05:14:05 AM »
Very nifty, tweaks, yet another cool useful project indeed.

Rich, that happens to us fairly often, and yes, we have a little 6 X 9 benchtop demag and we just drag it across large pieces of steel that we get shipped in as most "ground stock"  toolsteel is usually magnetic when we get it in.

Dave
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Offline RICH

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Re: Tweakie's De-Mag.
« Reply #6 on: May 29, 2012, 06:31:54 AM »
Thanks All,
Found an old bulk tape eraser. It's a transformer mounted in a metal box but the sides and top of the box is plastic. Has a momentary switch to turn on the
AC to the transformer. The transformer is different than a conventional one since the core is U shapped thus putting out a directional magnetic field / eddy current.  Not sure if it will be strong enough but worth a try.

Never throw out good junk............... :D
RICH