Author Topic: Tweakie's De-Mag.  (Read 6145 times)

Offline Tweakie

  • Jr. Member
  • **
  • Posts: 40
  • Country: gb
  • Super Kitty.
    • Tweakie.CNC
Tweakie's De-Mag.
« on: May 29, 2012, 11:00:13 AM »
A little project for a rainy day, all made with re-cycled items that would otherwise be consigned to landfill.

After some experimentation of wooden clock gearing using small neodymium 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 the way 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 dont 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 (basically from a transformer into a choke) 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. You could be fussy and include an on/off switch or really fussy and add a series connected switch (with a mains rated diode connected across the switch) - when closed it would de-magnetize and when open it would magnetize items.

I hope this little project may be of interest to others.

Tweakie.

Online philf

  • Hero Member
  • *****
  • Posts: 984
  • Country: gb
Re: Tweakie's De-Mag.
« Reply #1 on: May 29, 2012, 12:36:41 PM »
Hi Tweakie,

I like your demagnetiser - much simpler than mine.  :thumbup:

I made a demagnetiser some years ago but used a coil wound on a 50mm ID Tufnol tube. I used a transformer to power the coil. A push button switches the coil.



It is important not to switch the coil off until the screwdriver (or whatever) is some distance from the coil. If you switch off when the voltage is still on a high portion of the cycle the tool will be magnetised. Degaussing circuits in TVs and Monitors reduce the amplitude of the applied voltage slowly to avoid the problem.

I'm interested in your magnetic escapement - did you get it to work? Are you going to post any details?

I have a couple of battery powered tuning fork clocks with magnetic escapements but have always fancied making a pendulum version.

 :beer:

Phil.
« Last Edit: July 13, 2017, 02:37:10 PM by philf »
Phil Fern
Location: Marple, Cheshire

Offline David Jupp

  • Sr. Member
  • ****
  • Posts: 304
  • Country: gb
  • Teesside - UK
Re: Tweakie's De-Mag.
« Reply #2 on: May 29, 2012, 01:17:17 PM »
I did something similar a few years back, but only got round to trying it out recently (on a magnetised Torx key) - the really amazing bit is just how undramatic, yet effective it is.

I understand the theory of how it works, but it's still impressive that it does.

Offline Tweakie

  • Jr. Member
  • **
  • Posts: 40
  • Country: gb
  • Super Kitty.
    • Tweakie.CNC
Re: Tweakie's De-Mag.
« Reply #3 on: May 30, 2012, 01:30:38 AM »
Quote
I'm interested in your magnetic escapement - did you get it to work? Are you going to post any details?

Hi Phil,

When I get a bit further down the line I will post the details.

btw. neat bit of coil winding you have done and a very nice de-mag.

Quote
I did something similar a few years back, but only got round to trying it out recently

Hi David,

I think you are right - they are a tool that needs to be used so infrequently but when you need it - so nice to have.

Tweakie.

Tweakie.

Offline Fergus OMore

  • Hero Member
  • *****
  • Posts: 1012
  • Country: england
Re: Tweakie's De-Mag.
« Reply #4 on: May 30, 2012, 03:09:44 AM »
I might be going off at a tangent but excuse me if I have :doh:

I have a watch maker's demagetiser but it is often too small. Years ago, I saw a bigger machine made from a central heating pump. All that I can recall is that the guy removed part to add a flat plate to slide  magnetised parts across.

Can anyone throw some light on this please?

Thanks

Norman

Offline David Jupp

  • Sr. Member
  • ****
  • Posts: 304
  • Country: gb
  • Teesside - UK
Re: Tweakie's De-Mag.
« Reply #5 on: May 30, 2012, 04:51:57 AM »
More or less any AC fed coil should work - so yes a motor stator would work.  It is the slow removal of the magnetised item from a reversing magnetic field that 'does the trick'.