Magnetic tools

[earlgo]

There is an issue in my shop concerning the unearned magnetism in my tools: drills, tool bits, screwdrivers, taps, hex wrenches, etc. Is this a common problem and if so, how does one prevent it?
I built a demagnetizer from a small fan motor stator coil, but putting all the tools thru it one at a time is time consuming.
Any suggestions?

--earlgo

[Harold_V]

Magnetic tools aren't desirable in a machine shop, for obvious reasons. The chips that are attracted are a nuisance, and the magnetized parts are difficult to measure, as they interfere with feel.

I've always managed the problem with a small coil from an aquarium air pump. I have had little trouble with magnetism, however.
If you have a problem that is difficult to manage, I think it would be prudent to discover the reason, then take the appropriate step(s) to eliminate the source, assuming that's possible. Otherwise, a larger demagnetizer might make it a little easier, assuming it is large enough to accommodate several items at a time.

It's not all that hard to magnetize heat treated objects. Something as simple as a serious smack with a hammer can polarize (magnetize) the material, as it gets magnetized by the earth's magnetic poles.

Harold

[neanderman]

I have found that, for small parts, a sharp rap on something like an anvil will frequently not only knock the shavings off, but will frequently demagnitize the part.

[ctwo]

The last two posts seem contradictory.

I'm curious about it too. I was building a high speed spindle using a Chinese 10 mm ER11 collet tool holder. I discovered it was magnetized after heating the opposite end to orangish-red to anneal it for tapping the through hole. I do not recall any magnetism before or during the tapping, but now have an issue with chips and other tools sticking to it.

My experience with heating things as such removes magnetism, but then I also remember dropping the thing once on the concrete floor.

[Harold_V]

Hmmm. Heating should soften carbon steels, although how quickly they are cooled once heated may change that. Soft steel retains very little magnetism---generally not enough to be an issue. However, so long as there's any carbon in iron, or the alloy is steel, it does have the potential to retain a trace of magnetism.

Many years ago I produced more than 200 of the little pieces shown, below. I have posted this picture on a few occasions. The base piece (item on the left hand side) was made of carbon free iron, with the express purpose of being magnetic, but not retaining any magnetism. Armco iron was the specified material, iron that is commonly used for making laminations in transformers and motor armatures.

The first three latches are examples of the finished piece, but in various stages of machining. The finished and assembled product is on the right side. The "spike" shown is a common straight pin.

Harold

[Conrad_R_Hoffman]

Common problem. It's routine to demagnetize parts and tools. I often stroke a screwdriver with a magnet to attract when necessary, then demagnetize it after. If you deal with very small parts, periodic demagnetizing is essential. Not sure why you think it's time consuming as it only takes a few seconds per tool. Parts can often be demagnetized in bulk.

[earlgo]

There is something I am missing here. I am a mechanical engineer and never did understand electrical wizardry. The EE prof lost me when he said the holes go this way and the electrons go that way.
I bought a commercial permanent magnet demagnetizer by Wiha. It has two pass-thru openings, one for magnetizing and one for de-magnetizing. I could never get it to demagnetize, which is why I made the ex-fan motor demagnetizer, which, incidentally, works very well. However putting each tool in the core, turning on the unit and retracting the tool slowly beyond the gauss field limit is a bit time consuming.
So then the question becomes: how does one demagnetize a larger number of tools at the same time? For example, a set of number drills or a set of hex wrenches.
--earlgo

[GlennW]

Bigger coil and more amperage.

I once (20 some years ago) needed to de-gauss something that was nearly 4 feet in diameter and six feet long so I contacted the local NDT lab that did magnetic particle inspection.

They sent out a couple of guys with a rectifier and a length of 0000 cable. We made four loops around the object, put somewhere between 1000 and 1500 amps through it and dragged it off of the object. It was interesting!

The magnetism went away but eventually came back though.

I have an electromagnetic chuck on one of my surface grinders that goes through a de-gauss cycle when the part is released. I use the chuck to de-magnetize tools and such, as it works very well. Lay them on the chuck, energize it, release it, and it's good to go.

It would be a pretty expensive way to go though for your needs!

[Conrad_R_Hoffman]

Not sure why one would turn the unit on and off to demagnetize. Just move the tool into the field, then slowly out of it. Job done. Most strong demagnetizers do have a duty cycle limit, so you can't leave them on a long time.

[Harold_V]

I bought a commercial permanent magnet demagnetizer by Wiha. It has two pass-thru openings, one for magnetizing and one for de-magnetizing. I could never get it to demagnetize, which is why I made the ex-fan motor demagnetizer

That sends up a red flag for me, although I am not an EE, and may not understand this issue as well as I think I do.
Dragging a heat treated object through a magnetic field that is constant should magnetize the piece. I can think of no way it would demagnetize. That, typically, requires an AC field, with a gradual withdrawal of the item from the magnetic field as it changes polarity. Switching the device off with the magnetized item in proximity offers the chance it will still be magnetized, as the collapsing field will readily do so. I can only assume that's reliant on where the current is in regards to the sine curve. If you happen to turn off at the 0 point, that would not be true.

I agree with what Glenn said. A large demagnetizer will deal with multiple items, and do so quickly. The more power you have, the faster and more effective it will be.

Thoughts?

Harold

[mklotz]

If you don't want to invest in a commercial demagnetizer and you're a frequenter of yard sales and swap meets keep your eye peeled for a bulk tape eraser. They're an antique from the days of reel-to-reel tape recorders and are great for demagnetizing small tools.

With the tool near the eraser, turn it on and then remove the tool slowly to arm's length from the eraser before turning it off. [Magnetic fields, being bipolar, decrease as the cube of the distance so you don't need to get too far away before the field is negligible.] I always remove my wristwatch when doing this although I'm not sure that is necessary.

If you have a soldering gun, you can use that in a similar way to the bulk tape eraser for long slender objects such as screwdrivers or chisels. Stick the object in the loop of the soldering tip, but not touching the tip, turn on the gun and withdraw the tool slowly. For slightly bulkier tools I've constructed a 'tip' made from a loop of heavy copper wire.

As has been mentioned above, keep the duty cycle low on both of these devices if you use them.

[earlgo]

So this thing with the ceramic magnets is in reality just a fancy refrigerator magnet?
I wondered about that, but the marketing gurus got me.
Another $8 lost.

--earlgo