Help, my knife's gone magnetic

G

Grapevine

Joined
Mar 5, 2002
Messages
1,470
I just found out that one of my larger knives is magnetic. I don't know if it was this way when I got it or if it turned this way, probably the former.

Are there any inherent drawbacks to having a blade that's a magnet at the same time? I'm thinking that during sharpening it might hold on to all the steel dust that's scraped off of it...or would it actually repel the dust (reverse polarity and all)?

How do I de-magnetize it? I have this small magnetizer/de-magnetizer from the hardware store that works on screwdrivers, but it didn't work on the knife. Actually, after I couldn't de-mag with it, I tried putting the knife through its magnetizing area to see if there's any effect and it did make the knife more magnetic. Subsequent passes through the de-mag area only returned the knife to its former weaker magnetic state.
 
I would guess the only way to thoroughly demagnetize a knife is use a degausssing coil, or bulk tape eraser. You may be able to hold it near a big CRT monitor that degausses when turned on.

IMO, it doesn't much matter, because theoretically you could magnetize your knife by holding it North/South and hitting it with a wooden mallet. And in real life even if perfectly non oriented in magnetic field it would get magnetized due to random encounters with EM fields, tools, and other magnetic phenomena.
 
Cover the edge of the knife with tape such as duct tape.

Wrap a standard lamp-cord extension cord around the knife (this is why we covered the edge with tape).

Plug a 100W lamp in through that cord.

Turn the lamp on.

Sit back and read a book by the light of the lamp.

The alternating current in the cord will create an alternating magnetic field in and around the knife and that will demagnatize it.
 
You wouldn't want to do it with a knife, but other tools such as screwdrivers or pliers can often be demagnatized simply by dropping them onto a hard floor. Every now and then, you'll see an auto mechanic just drop his tool on the floor. That's why. It's picked up a bit of a magentic field which is annoying him, and so he'll drop the tool to get rid of that.
 
I use a bulk tape eraser. Works fine...
Where are you in NY? if you're close by, you could use mine.

Edited to add,
Hey Gollnick, I tried the lamp method, but it didn't work. I think I let it run for only 5 minutes. Did I do something wrong?
 
When you are using an AC coil, the magnetic field is switching 60 times a second. Conceivably if you just turned of the lamp at a certain time you left whatever the last cycles direction was on the knife.

You could experiment with slowly withdrawing the knife through and away from the coil. The theory being that as the distance increases you'll increase the likelyhood of randomly "imprinting" leaving a net magnetization of zero.

More than likely though is that a knife is not especially permeable and due to certain alloy elements may be resistent to being demagnetized without a stronger field.

Recording media is very easy to magnetize, hence the hand held units. I used to work for a shop that had a magneflux machine to check metal parts for cracks. It took some juice to demagetize an engine crankshaft.
 
Gollnick:
I thought about doing that, but didn't know the amount of time or whether that would make it an even stronger magnet.

DaveH:
Thanks for the caveats. I'll try slowly pulling the knife through.

MM:
I'm in Manhattan, 30s east side. If we're close enough and above suggestions don't work I may take you up on your offer.
 
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