# How to "De-Magnetise tools



## ddmunroe (May 31, 2014)

I've never really been able to solve this problem ... EG : My verniers at the measuring points touched a neodium magnet once and since then it pick's up all sorts of steel when placed anywhere. Always having to clean off fine bits before use now.
Same thing with allen keys these seem to be already magnetic.

My plight is how can I "demagnetise them.

I've done the usual google reasearch a while back and found articles about heating things on or past the "currie' point etc but in the case of my verniers I can't do that. I tried heating up the allen key in question but it made no difference.
The one thing I haven't tried is an actual demagnetiser, looks like a crack detection transformer type tool.

Has anyone had success in this area ?
Thank's
dd


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## JimDawson (May 31, 2014)

ddmunroe said:


> I've never really been able to solve this problem ... EG : My verniers at the measuring points touched a neodium magnet once and since then it pick's up all sorts of steel when placed anywhere. Always having to clean off fine bits before use now.
> Same thing with allen keys these seem to be already magnetic.
> 
> My plight is how can I "demagnetise them.
> ...



An actual demagnetizer will work fine.  I bought a nice, but really old (1930s maybe?),  tool room demagnetizer a while back for $50 and I don't know I lived with out it.  I hate magnetized tools.

I have heard that recording tape bulk demagnetizes will work, but I suspect they might be a little on the small side.

Also it might be possible to use an AC arc welder.  An old buzz box would be the best for this to get a nice clean sign wave output.  Wind the stinger cable around a piece of plastic pipe, connect the ground lead to the stinger, set about 80 amps, and turn on the welder.  Pass to tool through the pipe a few times.  It should be demagnetized.

I have used this trick to magnetize steel using DC from my Syncrowave, but have never tried to demagnetize.


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## Tony Wells (May 31, 2014)

Find an old CRT monitor and rob the degaussing coil out of it. Wire a momentary contact with of the proper rating and put the tool within the ring, hit the switch and slowly withdraw the tool. When it is a foot or more outside the coil, let go of the switch. Might take a pass or two, but will do it.


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## John Hasler (May 31, 2014)

Tony Wells said:


> Find an old CRT monitor and rob the degaussing coil out of it. Wire a momentary contact with of the proper rating and put the tool within the ring, hit the switch and slowly withdraw the tool. When it is a foot or more outside the coil, let go of the switch. Might take a pass or two, but will do it.



Or just salvage the PTC thermistor with the coil and use that.  The PTC has low resistance when power is applied and so initially alows lots of current to flow.  As it heats up its resistance rises so that the current exponentially decays to near zero.  As the current is AC the material in the coil is left with no residual magnetism.  That's how the degaussing coil removes magnetism from the shadow mask.

I've got some degaussing coils.  One of these days I'll get around to doing something with one of them.

You can also make a pretty powerful degausser from a junk induction motor.


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## mikey (May 31, 2014)

I use a tape demagnetizer, the kind they used for reel-to-reel players, and they work really well.


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## AlanR (May 31, 2014)

For small things I've just taken a coil of wire, like hook-up wire and wired it in series with an incandescent bulb, maybe 60 watts or so. That works fine.


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## TOOLMASTER (May 31, 2014)

mikey said:


> I use a tape demagnetizer, the kind they used for reel-to-reel players, and they work really well.


 x2
http://thumbs2.ebaystatic.com/d/l225/m/mlxHfDSUVGzAlBo4CDmE74g.jpg


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## JR49 (May 31, 2014)

If you have a gun style soldering iron, the kind that the soldering element has two prongs that connect to the gun. Pass the magnetized part in between the prongs of the soldering gun while its turned on , instant demagnetizer. Works great with anything small enough to fit between the prongs. take care, JR49


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## george wilson (May 31, 2014)

I have an old jeweler's demagnetizer that was used to demagnetize watches. Tony's suggestion is a good one if you can't find one of these. They aren't too common.


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## Tony Wells (May 31, 2014)

The PTC John is referring to above is a special kind of thermistor with a rather sharp cutoff, like a switch. Sure, you could do that, and it would work. I just prefer manual control, and like that rather than of a relatively rapid collapse of the field. Moving the item to be de-magged out of the field slowly seems to work better. But that's just me. His suggestion is sound.


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## John Hasler (May 31, 2014)

Tony Wells said:


> The PTC John is referring to above is a special kind of thermistor with a rather sharp cutoff, like a switch.



No, the whole point of the PTC is that it *doesn't* have a sharp cutoff.   The current and therefor the field decreases slowly as it heats up, just as it does when you move the tool being demagnetized away.  Otherwise it wouldn't effectively degauss the shadowmask in the crt.


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## Tony Wells (May 31, 2014)

That's not my understanding, John. Unlike most thermistors that are used to measure temperature, these used in degauss circuits act more as a switch. They are also used as thermal protection in some electric motors


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## John Hasler (May 31, 2014)

Tony Wells said:


> That's not my understanding, John. Unlike most thermistors that are used to measure temperature, these used in degauss circuits act more as a switch. They are also used as thermal protection in some electric motors



There are different types of PTC thermistors with different curves.

The PTC thermistor in a degaussing circuit is relatively large and has a low cold resistance.  When you first apply power it is cold and therefor allows lots of current to flow.  However, as its resistance is nonzero, it begins to heat up.  As it heats up its resistance rises and so the current decreases, eventually becoming too small to produce a significant field in the coil (but still large enough to keep the PTC hot).  Due to the thermal mass of the PTC the change is not instantaneous.  Thus the current ramps down over a period of a second or so.

http://en.wikipedia.org/wiki/Thermistor#Applications


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## Tony Wells (Jun 1, 2014)

PTC's used in degaussing circuits are capable of handling, in some cases,  30-35 amps initially, and some also contain an auxiliary heater. The standard rating time is 3 seconds for the cutoff, and the current flow at that point is only 200-300 ma. The idea is to pass the inrush current but then the resistance increased dropping the current. At only a few hundred ma, the coil only has a small field. Curve steepness is relative, and yes, I know there are many types of this thermistor, and consider a 3 second cutoff rather short. Not exactly fast switching as electronics go, but faster than a linear graduated thermistor as you be used to monitor temperature.

My only point was that I prefer to energize the coil for more than the typical 3 seconds, and withdraw the subject tool slowly from the field before the current is altered. Just a personal preference.


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## ddmunroe (Jun 2, 2014)

Can this coil be used as the demagnetiser. Ignore the smaller one it's just in the pic
What would the schematic look like ? AC power used I suspect.
What is going on in the "demagnetising" process
Thank you ... )
dd


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## John Hasler (Jun 2, 2014)

ddmunroe said:


> Can this coil be used as the demagnetiser.



No.  That's a toroidal transformer.  The magnetic field is all inside the donut.



> What is going on in the "demagnetising" process



The AC-driven coil produces a strong magnetic field that rapidly alternates direction and so causes the magnetization of the tool to alternate.  The alternating field is gradually reduced to zero leaving the tool unmagnetized.  Moving the tool away from the coil has the same effect as does gradually reducing the field.


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## ddmunroe (Jun 2, 2014)

John Hasler said:


> No.  That's a toroidal transformer.  The magnetic field is all inside the donut.
> 
> 
> 
> The AC-driven coil produces a strong magnetic field that rapidly alternates direction and so causes the magnetization of the tool to alternate.  The alternating field is gradually reduced to zero leaving the tool unmagnetized.  Moving the tool away from the coil has the same effect as does gradually reducing the field.



Thank's John Hasler
What would be the most effective build with regard to the AC coil demagnetiser / configuration EG : wire guage number of coils coiled over some thing maybe ?
dd


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## benmychree (Jun 2, 2014)

The shop that I apprenticed in had a big surface grinder (16 X 72) and we frequently ground hard steel, which takes on premanent magnetism from the magnetic chuck; to demagnetize, we flipped the reversing switch for the magnet and it would more or less cancel the magnetic charge so that work could be removed from the chuck, however this does not completely do the job, so we used a coil that was, I think taken from the generator end of a D.C. motor generator welding machine; the opening in the coil was about 4 X 5"; it was equipped with a cord to be plugged into a regular 110V outlet, and the part was passed through the coil several times and slowly withdrawn, and did a good job of degaussing the part.  Now, I have a B&S Micromaster 6 X 18 that has a electromagnetic chuck with a Neutrofier controll that offers both variable holding strength and the demagnetising feature that can be used to degauss nearly anything; I think it works by alternating the polarity of the current to the magnet and lessening the voltage at each reversal until it completes the cycle.  When I had the chance when the shop was finally shut down and sold off, I was able to make the demag coil my own ---


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## Localele (Jun 2, 2014)

Jump on flea-bay http://www.ebay.com/sch/i.html?_trksid=m570.l3201&_nkw=de-magnetiser&_sacat=0 and grab a De-magnetiser for screwdrivers and other small tools.These work and will handle your allen keys and probably the points of your verniers all for a few dollars.


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## ddmunroe (Jun 2, 2014)

Tony Wells said:


> Find an old CRT monitor and rob the degaussing coil out of it. Wire a momentary contact with of the proper rating and put the tool within the ring, hit the switch and slowly withdraw the tool. When it is a foot or more outside the coil, let go of the switch. Might take a pass or two, but will do it.



Hi Tony,
I now understand your post ... "CRT" was not in my abbreviation vocabulary. I'm not electronically inclined. 
Now I do have an old TV. I can take it apart to identify the degaussing coil and hook it up as you mentioned.
Will let you know how it works.
Thank's to everyone that posted I am considering everything you've said.
)dd


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## ddmunroe (Jun 3, 2014)

[h=3]Degaussing[edit][/h]If the shadow mask becomes magnetized, its magnetic field deflects the electron beams passing through it, causing color purity distortion as the beams bend through the mask holes and hit some phosphors of a color other than that which they are intended to strike; e.g. some electrons from the red beam may hit blue phosphors, giving pure red parts of the image a magenta tint. (Magenta is the additive combination of red and blue.) This effect is localized to a specific area of the screen if the magnetization of the shadow mask is localized. Therefore, it is important that the shadow mask is unmagnetized. (A magnetized aperture grille has a similar effect, and everything stated in this subsection about shadow masks applies as well to aperture grilles.)
Most color CRT displays, i.e. television sets and computer monitors, each have a built-in degaussing (demagnetizing) circuit, the primary component of which is a degaussing coil which is mounted around the perimeter of the CRT face inside the bezel. Upon power-up of the CRT display, the degaussing circuit produces a brief, alternating current through the degaussing coil which smoothly decays in strength (fades out) to zero over a period of a few seconds, producing a decaying alternating magnetic field from the coil. This degaussing field is strong enough to remove shadow mask magnetization in most cases.[SUP][21][/SUP] In unusual cases of strong magnetization where the internal degaussing field is not sufficient, the shadow mask may be degaussed externally with a stronger portable degausser or demagnetizer. However, an excessively strong magnetic field, whether alternating or constant, may mechanically deform (bend) the shadow mask, causing a permanent color distortion on the display which looks very similar to a magnetization effect.
The degaussing circuit is often built of a thermo-electric (not electronic) device containing a small ceramic heating element and a positive thermal coefficient (PTC)resistor, connected directly to the switched AC power line with the resistor in series with the degaussing coil. When the power is switched on, the heating element heats the PTC resistor, increasing its resistance to a point where degaussing current is minimal, but not actually zero. In older CRT displays, this low-level current (which produces no significant degaussing field) is sustained along with the action of the heating element as long as the display remains switched on. To repeat a degaussing cycle, the CRT display must be switched off and left off for at least several seconds to reset the degaussing circuit by allowing the PTC resistor to cool to the ambient temperature; switching the display off and immediately back on will result in a weak degaussing cycle or effectively no degaussing cycle.
This simple design is effective and cheap to build, but it wastes some power continuously. Later models, especially Energy Star rated ones, use a relay to switch the entire degaussing circuit on and off, so that the degaussing circuit uses energy only when it is functionally active and needed. The relay design also enables degaussing on user demand through the unit's front panel controls, without switching the unit off and on again. This relay can often be heard clicking off at the end of the degaussing cycle a few seconds after the monitor is turned on, and on and off during a manually initiated degaussing cycle.


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## Fabrickator (Jun 3, 2014)

I bought a "box" type demagnatizer from Enco and it works great.  No more problems!  They're really not that expensive with a 20% off coupon and free shipping they occasionally offer.  I keep it on my workbench. You can slide anything across the surface and also wave it along the tool post, bit or part while in your machine.

http://www.use-enco.com/CGI/INPDFF?PMPAGE=647&PARTPG=INLMK3&PMITEM=285-2505


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## Swarfmaster (Jun 3, 2014)

For most of the small stuff, i.e. screwdrivers, bits, tweezers, etc.,  my old Weller soldering gun always works great for demagnetizing.  Just pass the object thru the soldering loop and you are ready to go.    This actually does a better job than my old tape head demagnetizer for my reel to reel recorder.  good luck!


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## kd4gij (Jun 3, 2014)

Swarfmaster said:


> For most of the small stuff, i.e. screwdrivers, bits, tweezers, etc.,  my old Weller soldering gun always works great for demagnetizing.  Just pass the object thru the soldering loop and you are ready to go.    This actually does a better job than my old tape head demagnetizer for my reel to reel recorder.  good luck!









 For a little larger parts you can replace the tip with a loop of bare copper wire. I use 12 gage. You can also use that 12gag wire to solder with in a pinch


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## mws (Jun 4, 2014)

I used to service lots of Electron Microscopes and Nuclear Magnetic Resonance Spectrometers in another life.  All my tools had to be meticulously demagnetized (degaussed) or the results were disastrous and costly.  I still can't abide having stuff cling to my tools.  All the commercial degaussers I found were too costly, too small or had terrible duty cycles.

The best degausser I've found for shop use is an old fractional horsepower induction motor stator.  Remove the armature (obviously) and remove or open up the end bells to access the open stator ID.  Slip a piece of PVC pipe, or other non-metallic/conductive (not just non-magnetic) material to line the stator ID. This protects the windings from your tools and you from the windings. 

The current needs to be limited to about the normal operating load of the original motor. A big light bulb wired in series with the motor windings works well for this.  300~500 watt work lamps usually work quite well.   

Pass the tool to be degaussed SLOWLY through the motor frame (hold on tight) and continue to SLOWLY draw the tool away in a straight line until your about 2 -5 feet away before you turn off the power.  

Here's some background on the process.  Magnetization of any (ostensibly Ferrous) material is a realignment of the magnetic poles within it's structure.  The mechanical analogy is very much like bending a piece of ductile metal. You can bend any metal so far and it will return to zero. Exceed that degree of bend and it will take a set and remain bent, but not as far as you bent it.  To remove the bend it must also  be bent BEYOND the point where it is simply straight, so when it relaxes it is straight.  In magnetic parlance we call this hysteresis.  

If you've ever straightened a rod in the lathe by "leaning on it" with the tools post you know how it can be nicely centered when bending it over 360 degrees while turning and backing off while still turning.  The same principle is applied here by using AC current. Only AC fields can effectively demagnetize. The alternating field is "bending" or flipping the magnetic poles back and forth through 360 degrees repeatedly.  As the material is withdrawn from the field the peak to peak intensity reduces but zero is still zero. As the rotating field is reduced different poles are left in different states, or positions, as it were.  Hopefully, their positions will be evenly shuffled such that their sum magnetic field is zero.  Once you're far enough away from the field you should be left with just that, zero net magnetic polarization.  

Since induction motors have many poles, using an induction motor stator has the additional advantage of producing multiple loops of magnetic lines within it's core. This helps in getting all the parts more evenly demagnetized, especially good for odd shapes.  

Oh! And don't forget to leave your rings and watches, etcetera, somewhere else while playing with AC magnetic fields.    If your calipers have an electronic LCD readout I would remove it before degaussing. 

Hope this is helpful.  

Mark S.


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## ddmunroe (Jun 5, 2014)

Hi,
All of your replies have been very useful in helping me understand and solve my magnetic problem.
I've learned alot thank you.
Here is an interesting video, and you'll never guess where I found it ??? Right here in the video's section !
(Video showing what "MWS" was talking about in a simple form, "how to make your own demagnetiser")
Cheers dd :thumbzup:
[video]http://www.hobby-machinist.com/vbtube_show.php?tubeid=438&amp;sti=Homemade-Tool-Demagnetizer[/video]


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## Coomba (Jun 5, 2014)

Use the coil off of a solenoid valve.


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## mws (Jun 6, 2014)

Nicely done video. I use much bigger motor frames 1/2HP, 1/3HP, but the idea is the same. 

Solenoids without a core will definitely burn up in no time.  

Mark


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