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
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Gunner wrote:

What about a used magnetic vise from a surface grinder. Just flip the lever to turn it off and on.
ff
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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
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Gunner sez: I would like to be

Now that'sa some spicey magnetic field.
Bob Swinney
wrote:

lever
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."

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If you want something cheap that you can make in your shop, how about salvaging some TRANSFORMERS from scrap microwave ovens. The transformers have 2 windings, primary & secondary, wound on the center leg. If you cut off one end of the steel core you will have an "E" shaped piece left with both windings intact. The secondary has more turns and the primary has less resistance; you can use either or both in series to get the field strength you want with a usable voltage.
Microwave primaries often take up to 5 amps no load for short intervals. For DC you might want to limit it to 2 amps and even less for the secondary. You can put a bunch of these in series and might find a combination that would use rectified 110 vac.
Very cheap, does take some salvaging and a bit of work & experimenting.
--
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Here is an excelent DC coil design spreadsheet. It calculates amp draw, number of turns and magnet strength from the input voltage, core diameter, coil OD and wire size. my.execpc.com/~rhoadley/coildat8.xls
Looks like this guy knows more about electromagnets than anyone in his right mind should. His home page for electromagnets is http://my.execpc.com/~rhoadley/magindex.htm
Gunner wrote:

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
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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
================================================= please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com =================================================
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wrote:

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.
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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.
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On Sun, 25 Jan 2004 18:29:28 GMT, Ian Stirling

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.
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I have, and I get a different proof.
Halve the diameter, quadruple the resistance per unit length, quadruple the wire length in a given volume, multiply by 16 the resistance. Amp-turns drops by a factor of 4.
Consider a coil with a single turn, connected to a power supply. If you now cut the wire in half lengthways with an imaginary insulator, and leave the ends connected to the power supply. I hope it's obvious that the magnetic field remains unchanged. Now, repeat this process nine times until you've got 1024 wires. Field still unchanged. Wire them all in series, and run from a power supply of 1024 times the voltage, and each wire has exactly the same current going through it, but the coil is running on 1/1024 the original current, and 1024 times the original voltage.
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On Mon, 26 Jan 2004 11:22:11 GMT, Ian Stirling

Me too. We're in agreement.
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Works great if your insulation on the wire is of zero thickness.
--
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Well, yes. But it's a whole lot more correct than saying wire size is irrelevant, voltage is important.
Can also change results a bit if you go from round to square wire, or co-wrap smaller wire to fit into the gaps. Or of course if you change winding material.
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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
================================================= please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com =================================================
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wrote:

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.
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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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This is interesting, but it's only half the story. Lots of MMF is good, but pole design is even more important, if you want to pick stuff up.
I should think Gunner needs a line of alternating north and south poles, spaced about an inch apart if they are to be around 1/4 inch off the floor. It's the divergence, or the square of the divergence, of the magnetic field lines that determines how much pulling force you get.
-- Tony P.
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why DC? AC attracts dirt just as well, with the bonus that it leaves nearby machine tools non magnetic after it passes by.

better get them properly in phase though.... but AC will still work fine
swarf, steam and wind
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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.
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