demagnetizing 4140?

You could wave a magnet in its vicinity.

No kidding -- I have successfully demagnetized screwdrivers with a strong permanent magnet. Stroke it a few times with one pole, then reverse the magnet and stroke it a bit further away. Keep doing this until you're waving the magnet in the air well away from the part.

It _won't_ demagnetize the thing completely, and may not work at all for complex shapes, but it should make things better.

I'll give that a shot, thanks.

Well, right now it's not that complex of a shape, but it will be shortly. I'll demag it first then.

Thanks Dave

"Tim Wescott" wrote: (clip) Stroke it a few times with one pole, then reverse the magnet and stroke it a bit further away. Keep doing this until you're waving the magnet in the air well away from the part. (clip) ^^^^^^^^^^^^^^^^ You are, in effect, producing a gradually diminishing AC field. which is what a degaussing coil does. As you say, it might be only partially effective, and it would take time. How about wrapping a coil in your steel bar, and applying a little AC voltage, and then reducing that, with a Variac? Or look around for an existing coil to use? Lots of mechanical devices use solenoids to make things move--for example, the automatic locks on car doors. The important thing is, you need to produce a field that is as strong as the one in the piece of steel, that reverses a lot of times, getting gradually weaker and going to zero.

Easy, if you have a D C welder. Simply wrap the lead around the piece several times and hold it in a dead short. Check the piece and if it's more magnetized, just reverse the polarity and short again. Keep doing this until the magnetism is gone. Learned this from an old railroad man back in the

It just seems intuitive that it would work better with an AC welder. The tool MAGnetizer I used to have used a DC coil in dead short with a consummable fuse to break the circuit rapidly, and cause a strong 'ring' in the coil as the field collapsed.

Breaking the short on a DC welder might even strengthen the magnetization of the piece. Reversing the polarity doesn't guarantee that you'd not swing the work to the opposite polarity, leaving it still magnetized.

LLoyd

How big is the part? For very small parts, I use a Weller soldering gun, the kind with the two posts sticking out the front, and the copper "wishbone". If necessary, I can make a ring of #12 wire that has a bigger opening than the standard element.

For larger pieces, do you have an AC TIG welder? If not, then try an AC buzz-box. Make a loop of several turns of ground cable big enough to surround the part, and short the electrode holder to the ground clamp. If TIG, set it for something like 50 A, if buzz-box, set it for the lowest current possible. Place the looped cable around the part, and turn on the welder, or step on the TIG pedal. Remove the cable while the welder is still on, then turn it off when the cable is away from the part. You may have to repeat this process several times in different starting orientations to completely demagnetize the part. You may have to turn up the current if the amp-turns are not enough to do the job.

What you are doing here is passing an AC electromagnet over the part, and gradually drawing it away. The 60 times per second alternating field of decreasing intensity gradually reduces the remanent field to zero. (When I say gradually, it only takes a couple of seconds.)

Jon

Roughly 8" x 1.056" x 1.200" before I started removing chunks, curls, & chips...

Doesn't apply in this case, but thanks, I do have that type of Weller iron (along with 3 other Weller irons - all surplus but good stuff)

I've got a neighbor who is a blacksmit, I bet he can help me out on this one. Thanks.

Right, so I'm inducing a bias frequency as a B1 to change the B0. Funny how I tend to forget that all that schooling translates into real world, sometimes. I guess it's because so many times it doesn't.

Yes, it takes time -- but less time than buying or building the right tool.

Were I to do it all the time I'd get or make the right tool.

I really think that you CAN do this with a Weller gun. You will need to make a custom copper coil to fit around the part, but it will work on something this size. You need a coil about 1.5" diameter, with one or two turns. Hold the part at the very end with pliers in one hand, and turn on the soldering gun. Pass the part through the copper loop all the way, then draw it back fairly slowly, so it takes several seconds to pass all the way through the coil. When the part is at least 6" away from the coil, turn off the soldering gun. The part will definitely be demagnetized. This procedure will degauss anything but a high- strength permanent magnet.

I use this setup all the time to degauss small tools that occasionally pick up a strong magnetism.

Jon

"Dave Hinz" wrote in message news: snipped-for-privacy@individual.net...

Electric motor rewinders have a test unit commonly called a "growler". This was for testing armatures and was basically a coil with poles pieces. I used to use one to demagnetise any rotating part of our equipment when working in the oil well logging industry. Easy to use, we just turned on the switch while some distance from the part, moved close to the part and held it for a while then backed away before shutting it off. It was usually successful, though I heard that one of the trucks had been hit by lightning and had to be scrapped, as it not be demagnetised to an acceptable level.

Dave TV repair shops often have degaussing coils used to remove any magnetism from TV tubes; it's worth a shot if you're friendly with a TV repair man. Martin

How big a part?

An AC coil is the answer in any case. Preferably one that you can hold the part in and then draw it away from while the coil is still active.

For small items, the frame les the rotor of a cheap fan or blower motor will work fine, just place the part oin the feild between the poles and withdraw it slowly away. A bunch of wraps of wire and an AC welder would serve for larger items.

Guys to talk to. Engine rebuild shops that magnaflux cranks or heads. The unit they use (Parker Probe, pretty commonly

can demag as well as magnetise, and is quite portable. Non Destructive Testing or Inspection NDT/NDI shops. A fixed Mag particle bench can run several hundred amps through it's coils. (Leave your credit cards in the changeroom, or else. Watches too!) Typical coil on a fixed bench unit should allow you to run a decent sized lunch box through it.

Watchmakers, clockmakers. Magnetism is a very bad thing, so they demag parts and tools as required. A little AC coil again, sometimes in the form of a coil, sometimes the coil is buried in a nice flat plate that looks like a small benchtop weigh scale. In either case the part is placed in the field and draw away slowly to minimise the chance of imparting a bit of magnetism into the part as the field collapses.

Cheers Trevor Jones

If you have some grinding left to do on it, wrap a heavy extension cord [the longer the better] around it, plug in the grinder, and go to work on it.

By the time you're ready to reposition it for the next round [having, I hope, NOT ground through the wire...], the piece should be degaussed.

Otherwise, just run a piece of machinery that's plugged into the coiled cord and, periodically, check the level of magnetism in the piece.

Got a welder? Wrap one lead around the piece, on AC and strike an arc with the stinger in a piece of scrap on high amps

Gunner

"The importance of morality is that people behave themselves even if nobody's watching. There are not enough cops and laws to replace personal morality as a means to produce a civilized society. Indeed, the police and criminal justice system are the last desperate line of defense for a civilized society. Unfortunately, too many of us see police, laws and the criminal justice system as society's first line of defense." --Walter Williams

Every colour TV is fitted with a demagnetising coil which is designed to do just that when connected to normal

50/60Hz power.

Raid a junk TV for this coil which is wrapped round the large flare of the display tube. As removed it is a large diameter coil. Twist the coil so that it is re-arranged into a three turn loop (this is the same trick as twisting a vee belt into a three turn loop to make it smaller for storage).

You now have a very convenient demagnetiser - pass the workpiece slowly (a second or so) through the coil and it will do a thorough demagnetising job. The coil is short time rated so don't leave it on too long - 10 to 20 sec is OK.

Jim

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Like coiling a bandsawblade. Clever!

You need a coil of wire!--with a hole big enough to pass your bar through it..heavy wire--like 12 or 16 gage--more turns the better hook up a duplex outlet recepticle in series with it--plug in a couple of clothes ironing irons, or a space heater --something that will draw

1000 watts or so(so you don't burn out the coil)-plug it in & pass the bar through it --and on past it. I have a primary coil out of an old neon sign transformer that I've been using for many years.

NOTE--WHEN THE COIL IS FILLED WITH IT'S LAMINATED IRON CORE, IT DRAWS PRACTICALLY NO CURRENT--WITHOUT THE IRON CORE IT WILL BURN OUT VERY QUICKLY. THAT'S WHY YOU LIMIT THE CURRENT WITH THE IRONS, OR HEATER RESISTANCE ELEMENT. JJW

Tom Miller wrote: