How do I make an electromagnet?`

I need to make a "picker upper" for swarf, nuts and bolts etc. My shop floor is packed dirt, but it does tend to embed swarf and of course nuts, bolts, drill bits and all manner of wierd stuff.

Id like to make a 110vt STRONG 18" wide electromagnet that I can mount on a couple of wheels and push around like a push broom.

While I have some idea how it works..I dont have a clue to the right way to actually make one. Anyone ever make one before?

Gunner

" ..The world has gone crazy. Guess I'm showing my age... I think it dates from when we started looking at virtues as funny. It's embarrassing to speak of honor, integrity, bravery, patriotism, 'doing the right thing', charity, fairness. You have Seinfeld making cowardice an acceptable choice; our politicians changing positions of honor with every poll; we laugh at servicemen and patriotic fervor; we accept corruption in our police and bias in our judges; we kill our children, and wonder why they have no respect for Life. We deny children their childhood and innocence- and then we denigrate being a Man, as opposed to a 'person'. We *assume* that anyone with a weapon will use it against his fellowman- if only he has the chance. Nah; in our agitation to keep the State out of the church business, we've destroyed our value system and replaced it with *nothing*. Turns my stomach- " Chas , rec.knives

Reply to
Gunner
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What about a used magnetic vise from a surface grinder. Just flip the lever to turn it off and on.

ff

Reply to
ff

Reply to
Glenn Ashmore

First off they do sell what you are looking for, using strong permanent magnets, switchable so you can drop the load of magnetic trash when you want.

However seeing as this is a roll-yer-own ng, I would suggest the following:

First off you will need some kind of rectifier to convert the ac to dc, a small RS bridge or whatnot. Then probably a resistor to limit the current flowing so the windings don't flow too much current and burn out. And of course a fuse to keep the entire thing from catching on fire.

I would consider starting with two pieces of plain CRS, each about three inches, by 18 inches, by maybe 1/8 or

3/16 thick. These will be the pole pieces and should be mounted edge-up, with about an inch or maybe 3/4 inch separation. You will either need to find some many-turn coils from some old solenoids, or wind your own coils on some steel pucks, that can be inserted in between the pole pieces. Key here is to make the magnetic circuit completely through steel, except at that tips of the sweeper edges. So you will need to try to find some ready made (scrap) coils that have the steel poles exposed, and are no more than an inch or less long. Then you mount a bunch of them (maybe one every six inches or less in between the two steel strips and somehow clamp them up in there, solidly.

The more amp-turns you can put on the coils, the stronger the resultant field at the tips of the sweeper poles. Oh, and they have to be wired up to add field btw, in series probably. If you have too many turns of too-fine wire, the resistance will be too much and you won't flow enough current, even with no field control resistor, to get enough magnetism. If the wire is too coarse, there won't be enough turns to generate enough field, and the current flowing will be so high that you will burn a lot of power in the resistor. So the design idea is to find someplace in between to get an amp or two of total current, at about a hundred or so volts. So you need to have the total resistance below about a hundred or so ohms.

If you could find something like an old tape head demagnetizer or two you *might* find what you are looking for in there. I've never had one broken apart to look at though.

Another approach would be to simply machine steel separator disks of appropriate size, and slip some RS spools of copper wire over them when you assemble it all. You need to be able to dig out the center of the spool winding though.

I take it the idea is to make for free, or nearly free, what could be purchased for a few hundred dollars. Interesting project.

Jim

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Reply to
jim rozen

A usefull thing to know is that for a given power in a certain shape, wound with copper wire, the magnetic field will be constant.

So, however you wind a solenoid, if it uses 110V at 1A, or 110A at 1V, the magnetic field will be the same. DC may work a bit better than AC, a bridge rectifier may be an idea.

Reply to
Ian Stirling

For given coil voltage and coil volume magnetomotive force does not depend on wire size. More turns of fine wire has higher resistance so lower current but more turns so ampere-turns stays the same.

Reply to
Don Foreman

Maybe better to state "for a given coil power", rather than voltage.

The above is strictly correct, but is misleading unless you realise that it implies that you have to put coils in parallel to keep the same coil volume.

Reply to
Ian Stirling

I have. They're just coils of wire and a steel magnetic circuit. A design for yours would depend on what you can scrounge in the way of magnet wire or coils. If you want to wind the coils, you can wind 'em on a lathe. For a DC magnet you can use ordinary mild steel, no need for laminations like you see on solenoids and transformers.

One consideration might be how much heat is acceptable; a 2 amp 110 VDC coil will be dissipating about 200 watts so it'd get kinda warm after a few minutes.

Jerry and I contrived an eddy-current brake for a dyno using alternator coils for the electromagnet. They typically draw about 5 amps at 12 volts, so 10 of 'em in series would draw 5 amps at 120 volts, 20 of 'em would draw 2.5 amps at 120 volts, and so on.

If you could run it off a battery charger or transformer/rectifier, then I bet 4 alternator coils in parallel (10 amps) might make a pretty strong electromagnet of the form you desribe. I'd make the pole pieces out of steel at least 1/4" thick so it doesn't saturate.

Assembly method isn't critical; you can bolt it, tack-weld it, or even glue it together.

If you want to wind yer own 120-volt DC coil(s), see w hat you can scrounge in the way of magnet wire. I'd say something around 28 gage gage would be about right. A pound of it would be plenty.

More if you're interested.

Reply to
Don Foreman

Coil voltage, not power. More turns of finer wire in same volume will draw less current hence less power at given voltage, but mmf will be the same because mmf is amperes * turns. Write the equations; the proof is simple.

That does, however, indicate that he'll get less heating for given mmf with more turns of finer wire. In fact, for given voltage and coil volume power will vary inversely as the square of the number of turns while MMF remains about constant.

One actually gets slightly less MMF per volt per unit volume with more turns because insulation thickness occupies a greater percentage of available volume, but that's minor until you get to wire finer than he'll want to mess with, like #40 and finer.

There is no implication of parallel or series connection. Single coil, same dimensions, just different wire sizes.

Reply to
Don Foreman

Hey, Gunner, there's all kinds of magnet wire on Ebay if you want to "roll yer own". Looks like 10 bux worth would do ya just fine.

Reply to
Don Foreman

Right, but he is limited by the 100 or so volts available, so that sets an limit on how fine the wire can be. (upper or lower bound depending on if you are talking gage or diameter!).

And he probably does not want to be running many many amps through the thing, so that sets a limit on how large the wire can be. Practically speaking, this means he will be scrounging different items to obtain the pre-formed coils that he's going to use.

Jim

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Reply to
jim rozen

1.Attach a couple loudspeaker magnets to a "broom" use a piece of paper to cover the magnets.
  1. Find an old starter solenoid and take it apart.
  2. Use thin insulated wire and mild steel core attached to auto battery.

B W

Reply to
bw

I have a couple, but they dont have a very big magnetic field..ie you just about have to touch it before it attracts. I would like to be able to not drag it through the dirt, but an inch or so above it.

Gunner

"As physicists now know, there is some nonzero probability that any object will, through quantum effects, tunnel from the workbench in your shop to Floyds Knobs, Indiana (unless your shop is already in Indiana, in which case the object will tunnel to Trotters, North Dakota). The smaller mass of the object, the higher the probability. Therefore, disassembled parts, particularly small ones, of machines disappear much faster than assembled machines." Greg Dermer: rec.crafts.metalworking

Reply to
Gunner

I want to be able to plug it into an extension cord. I understood before hand, that a rectifier would be required. Think of a push broom on two plastic wheels that you can push around the shop, then when its got all sorts of stuff stuck to it, hold it over the trash can and turn it off.

Mounting the thing inside a piece of PVC pipe with a couple axles hose clamped etc to the outside would make a clean and easy package to handle and assemble.

As is obvious, I know dick about electromagnets, so I asked here, where all the really bright boffins hang out.

I have one of those hand magnets with a loop handle and a t-handle inside, that you sweep over your nuts and bolts, then pull the t-handle to release the field. But its pretty small for dragging around the shop .

What got me thinking about this was having to pull a steel sliver out of a cats paw yesterday, then last night while fixing my DRO, dropping the case screws into the dirt..and not finding them all.

Gunner

"As physicists now know, there is some nonzero probability that any object will, through quantum effects, tunnel from the workbench in your shop to Floyds Knobs, Indiana (unless your shop is already in Indiana, in which case the object will tunnel to Trotters, North Dakota). The smaller mass of the object, the higher the probability. Therefore, disassembled parts, particularly small ones, of machines disappear much faster than assembled machines." Greg Dermer: rec.crafts.metalworking

Reply to
Gunner

Would one of these work?

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R, Tom Q.

Reply to
Tom Quackenbush

Do it the easy way. Get some neomydium boron super magnets. Mount them on a strip of thin plexiglass. Put a second thin strip over the magnets so you can just pull that strip off to empty the stuff that is stuck on there. Get fancy and put some roller wheels on the ends of the strips so that the magnets are about 1/2" to 3/4" above the floor. Roll the "broom" along to pick up stuff. Pull the strip to empty it. Or just buy a bunch of the round ones, about $20 per hundred on ebay, and those suckers will pick it ALL up.

I dropped a pouch full of staples I pulled out of the Christmas lights on the shop floor. Oh shit. Then I pulled out a rod of about 50 neomydium boron magnets, and had them all picked up in a jiffy. I love these powerful little magnets. Useful for a thousand things, and don't need a power supply cord.

Steve

Reply to
SteveB

I know this isn't what you asked, but that's the way that this NG works :-) :

How about microwave oven magnets? At our dump there's probably 3-4 MWO's every week. The magnets are about 2" in diam, so take 9 of them side by side (flat) and fold some aluminum flashing around them box-like. You then have a 2 x 18 x 3/4 aluminum box. Put this inside another aluminum, or plastic, box with wheels and a handle (or just a rope). Drag or wheel this around the shop, hold over the trash can and pull the inner magnet box out. Works like your hand-held with the release handle.

Being able to drag it without an air gap increases the effectiveness.

And that's the way that I'd do it, Bob

Reply to
Bob Engelhardt

OK, I wrote out the equations. You're right. As wiresize gets smaller, both MMF and power dissipation go down, MMF directly as wiresize and power as the square of wiresize with power dropping faster. For given available volume I guess ya'd pick the largest wire size that doesn't exceed acceptable power dissipation and thus operating temperature.

Winding coils is no big deal, and there is lots of magnet wire on Ebay. I usually make coil forms out of delryn on the lathe but I've even made them out of glued-up bits of cardboard.

Reply to
Don Foreman

This sounds like the best idea. No power cord to drag around, and you will get just as much field as an ectromagnet if done right.

Jim

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Reply to
jim rozen

If I were doing this, I would use perm. magnets as another poster has suggested. But if for some reason I wanted electromagnets I would simply buy spools of wire and pop them over steel cores, made to fit. Key with this idea is that one has to be able to access the start of the winding somehow!

Jim

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Reply to
jim rozen

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