[How do I?] Demagnetize a mill vise

[Friendly non murdering Sword]

So I bought a new mill vise from a friend:



I'm very happy with the condition and the pricepoint I got it at. I placed the vise on my mill and wanted to do the first testrun when I noticed... the darn thing is magnetized. Mainly the fixed jaw where for example a thin piece of sheet metal or parallels would stick to and me having to pull them off. The base is magnetized, too but much less so.

I don't own any demagnetizers because I have never run into this problem. So how do I best demagnetize a 5,9" x 20,5" vise?

 

[JimDawson]

If you have an AC welder, the old transformer type, wrap a couple of turns of the welding cable around the vice and do a little practice welding, at high current, on some scrap for a few seconds. Repeat if needed.

 

[Friendly non murdering Sword]

If you have an AC welder, the old transformer type, wrap a couple of turns of the welding cable around the vice and do a little practice welding, at high current, on some scrap for a few seconds. Repeat if needed.

Unfortunately I only have an Inverter type TIG welder, with HF mind you but no AC for aluminium.

 

[JimDawson]

Maybe you have a friend with an old AC welder? I don't know how else to do it with normal shop equipment.

 

[homebrewed]

Some have made demagnetizers using rotating magnets arranged in an alternating N-S pattern. A drill or lathe can be used to spin the assembly whle you bring the piece up close and then slowly pullt it away. That woiuld be very similar to the AC-based demagnetizers.

Iron and steel items will be attracted the assembly no matter what so it will be necessary to keep a good grip on your part while you do this.

The idea is siilar to the AC-based units. I bought one of that type a number of years ago so I could demagnetize tools when working on machines that are senstive to magnetic fields, like scanning electron microscopes. I don't use it often but it's nice to have around.

For smaller items like screwdrivers you can use a transformer-based soldering gun, in much the same way as using an AC welder.

Another DIY approach woulld be to find an old microwave oven transformer (MOT) and separate its primary and secondary halves. Plug the primary circuit into an AC line and pass the transformer poles over the item you want to demagnetize. This is pretty much the same thing as commercial AC demagnetizers.

The coil part of a 110V solenoid also might serve the purpose. If you choose to wind your own coil you probably will need a way to limit the current so it doesn't burn up, or figure out how many turns you need to get enough inductance to limit the current. If that sounds mysterious, you probably don't want to go down that path.

It should go without saying, but any circuit using 110VAC or higher can be danerous to operate unless you know what you're doing and take appropriate precautions.

 

[Bi11Hudson]

Expanding on the microwave transformer a little, the idea is to get a very powerful current flow at a low voltage. There are dozens of videos on the web of "jerry rigged" welders, both stick and spot welders. I have one I set up for resistance soldering. Any of these would serve the purpose.

On mine, I removed the high voltage winding, a given for any such project. Be careful not to nick the primary, a piece of flashing tin will suffice if you're easy with the hacksaw. Once the upper half of the case is clear, use a piece of automotive starter cable or something about three eighths inch diameter over the insulation. Copper is preferable but aluminium wire will work. Three or four passes of the cable through the frame will suffice for a demagnetizer. The output voltage is very low, far below six (6) volts. On mine it is around 2.5 volts. . .

I highly recommend some sort of case, but the big issue is to protect the line coltage taps. Shrink sleeving or at least tape them well. A third wire for the ground plug is a safety issue. Hopefully you'll never need it, but if you do you can thank God you went to the trouble. Any point on the frame will suffice. . .

The "degaussing" coil can be more of the same wire as what was used on the transformer. I have leads made from AWG-6 cable, type "SO" I think. Make a couple of turns, more if you have the extra cable. There is no need at that low a voltage for short circuit protection. Just make the wraps and tape them together so it can be handled. Power on the transformer and slowly remove the coil from the device. Or the other way around if your setup is that way. Five feet or so should be sufficient clearance. It may take several attempts for results, the amount of magnetism and the reluctance of the steel can will affect the degaussing. Some steels (iron content) have higher or lower reluctance.

The effect is the same as using a soldering gun (I use a Weller D-550) to demagnetize a screwdriver. Just a bigger chunk of iron. The contraption will serve quite well without a case but if you intend to keep it handy for welding or soldering, it really should have a case. For consideration, mine outputs several hundred amps at full line voltage. I use a "Variac" on the input to control the heat. The Variac is limited to 7 amps, I just kept adding turns until a "bolted short" approached that limit. I used an analog "Amprobe" to measure the current as I worked. (I'm old school and don't like digital instruments.)

The theory is the same as for an "old timey" color TV with a CRT. It often was a practice to use a majical coil in front of the screen to true up the color projection. That coil was a smaller version of what is suggested here.

.

 

[homebrewed]

Ebay has plate demagnetizers starting at about $45, not including shipping. For comparison purposes, you can get a suitable MOT for about half that, or even for free if you scrounge around. It has to be one of the older types with nothing but iron and copper in it. Newer microwaves use switching power supplies that aren't so easy to repurpose. Even if you rewire the transformer, the output would be high frequency AC. You might end up with an induction furnace instead of a demagnetizer!

If you have one, or know someone who does, or find one on Craigslist or the like, the old Harbor Freight flux-core wire welders were (are?) AC output type welders so also would be a good starting point.