I store the chuck key for my drill press on a magnet stuck to the side of the drill press itself. At some point, I inadvertently touched a tool bit (a 1/2" counterbore) to this magnet, and now the bit itself has become magnetized. Now, when I’m using it on steel, the chips gather on the tip of the bit and obscure my workpiece, requiring frequent clearing with compressed air.
Is there a cheap/easy way to demagnetize my tool bit?
Buy a tool magnetizer, one of those small pair of magnets with a channel for magnetizing screwdriver bits etc. Used correctly, it will demag bits, too.
An old-school cassette/videotape demagger will work, too. You can probably find one at Goodwill.
I had a magnetize/demagnetizer I think I got at Radio Shack. It magnetized better than it de-magnetized. I don’t know where it is now, probably stuck to a piece of steel somewhere in the basement if I still have it.
Anyway, lacking some device like that you can heat the chuck key in an oven to some temperature I don’t recall. I don’t think heating to the 500F available in most ovens and then letting it slowiy cool will soften the metal significantly.
One of those funny magnetiser/demagnetiser devices might work, but as noted, they seem to be better at the former than the latter.
The trick with temperature is to raise it above the Curie point. However for high carbon steel you are looking at over 1000K (say 1500F.) This is possibly too close to the transition temperature between Austentic and Martensetic steel. However high speed steel has a tempering temperature of this order, and is designed to get this hot and remain strong. So it might work. But this is really hot. Bright cherry red hot.
The usual demagnetiser is a coil energised by AC current that reduces the strength of the current (and thus the amplitude of the oscillating magnetic field) over a second or so. Trouble is that even making one would likely cost more than the bit.
:dubious: What is the “correct” way to use a magnetizer for demagnetizing purposes?
For perspective, this is just a $30 tool bit, and I’m probably halfway through it’s useful life. So any solution that costs more than $15 (actually, more than ~$5 if we consider the cost of my time) is probably not worth it.
As I recall my high school physics, you can just hit it a couple of sharp blows with a hammer.
I have some metalworking experience, and I would never try to demag a high-speed tool by heating it. Maybe a truly expert machinist/metallurgist could do it. But an amateur is likely to create a dangerously flawed tool.
Radio Shack and others sold these by the truckload back in the day. I’d wager one could be found cheap. (They are just a transformer with one bar lopped off, so that you have sort of a fat pitchfork of three laminate pillars with the coil on it. It’s used by placing it near the item to be demagged, turning it on, and slowly moving it away, four or five feet, before turning it off. Repeat a few times and the ferrous item should be pretty dead magnetically.)
I remember that too. Never tried it myself so can’t attest to the accuracy of that. But if you already have a hammer, it costs nothing to try.
Wow! You’re right. Don’t recall where I saw something about this, maybe softer iron alloys, but from the chart in the link I don’t see anything with iron close to that. This part aboutapproaching the Curie temperature from below might explain it, except I don’t know what it means.
See if a TV repairman can degauss your bits. 
You’d be paging Don Knotts in Pleasantville. TV repair hasn’t included degaussing (CRT screens) for at least a decade.
Maybe an old line shop.
As a child I accidentally magnetized a spinning metal Christmas ornament to the point where it would no longer spin due to magnetic attraction. I asked my Science teacher how to de-mag it, and he said to boil the components until they were no longer magnetized. Never got the chance to try this method as step-mom tossed it in frustration.
If you have a soldering GUN (not an iron/pencil), hold the ass end near your bit, turn it on/squeeze the trigger and back the gun slowly away from the bit. Do not release the trigger until you’re +/- 8-ish feet away. Should collapse the field.
Just a wild guess.
Wrap the cord of a high power appliance, like a heater around the bit. As the appliance is running, move the bit slowly back and forth in the coils of the cord.
The 60 HZ alternating field might lessen the magnetic properties.
Maybe wear insulated gloves. I am not sure if a current might be induced.
That’s what I came in to say. I had some kind of science kit at home. It probably had a project about making electromagnets or something. Eitherway, it mentioned that some things will retain their magnetic properties but hitting them a few times with a hammer should ‘fix’ it.
You might try that first. I don’t know if it’ll work, but it’s worth a try. Hold the ‘geared’ part with a pliers so the ‘flat’ part (that you would hold with your hand) is on a bench and smack that part with a hammer a few times and see if it makes a difference. As long as you don’t hit it really hard or on the part that meshes with the chuck, I doubt you’re going to hurt it. Even if you do, it looks like a new one can be had for about $5 on Amazon, probably less than $10 at Home Depot.
A hardened tool bit might shatter if whacked with a hammer or such.
Because the cord contains both legs of the current (ie active and neutral) the magnetic field will be zero - as the two legs cancel one another out.
What not to do! Homemade Degausser - YouTube :eek:
"Made from a microwave oven transformer. Uses 240v mains electricity.
Pls be careful if you decide to do this - mains electricity will kill you."
The cancellation will be imperfect, since the two wires in the cord are separated by a non-zero distance. So if the part is small, and the cord is right next to it, and the cord isn’t twisted, then this could conceivably produce decent magnetic fields in the immediate vicinity of each wire, which would fade away as the tool bit is slowly withdrawn from the coiled cord.
Taking it a step further, I could make a custom extension cord in which the two wires are split apart, then coil just one of the wires around the tool bit.
This is the kind of cheapo thing that I think might be worth trying.
You would need to get the wires quite some distance apart. The field strength of a pair drops off as the distance to the fourth power. Not only that, whilst they do form a pair, even a loose one, you can’t usefully gain the multiplication of the field that occurs with coiling the wire. The field strength goes up as the square of the number of turns so this isn’t a trivial loss.
In order to demagnetise a ferro-magnetic object you need to place it in a field that is stronger than the field it itself is creating. This is going to require a lot of current and a lot of turns. Which is why commercial demagnetisers use a large coil wrapped around a steel core. You need to drive the object around the entire hysteresis curve and slowly drop the field strength as you do so. If you don’t get to the edges of the curve you won’t reduce the residual magnetisation. left after the field is removed.