I have a bunch of really strong rare earth (Neodymium) magnets, along with various ceramic ones. I’d like a safer place to keep them; right now they’re sitting in the open so that I remember to not set any magnetic media or CRT devices near them.
If I was to make a box for them, how thick of steel would be necessary? Do I need to weld it, or would screwing it together with butt joints be good enough?
The largest Neodymium ones are a 3/4" sphere and 1" x .4" x .4" rectangular prism, but I will undoubtedly have larger ones at some point.
You may have trouble taking them out of a steel box (although I understand what you’re trying to do)
Don’t RS components (or somebody) have a suitable steel project box that might suit?
[3F11] Scenes from the Class Struggle in Springfield
Homer: [gasps] Look at these low, low prices on famous brand-name electronics!
Bart: Don’t be a sap, Dad. These are just crappy knock-offs.
Homer: Pfft. I know a genuine Panaphonics when I see it. And look, there’s Magnetbox and Sorny
** Mangetout**I keep them stuck to galvanized steel sheet right now. They stick well, but they can always be slid off. It’s not blocking all the magnetism. RS Components don’t appear to do business in North America.
Nobody? Anybody? There’s got to be someone with magnet experience. I have found out that the distance between magnets and box influences the thickness of steel necessary, but I still haven’t found any equations or rules of thumb.
Never played with a big rare earth magnet, have you? The 3/4" sphere will alter a monitor from 18" away, wood or no wood. A 3/4" diameter by 1/2" cylinder will pull a 1/16" cube around a table top, with the table 1" thick wood and a 1" air gap between the big magnet and table.
They’re strong enough that I accidentally dicovered the direction of the lines of flux of the Earth’s magentic field one day, just playing with them. They’re not parallell to the earth’s surface at this lattitude. Just spinning one on a table will tell you which direction is north, if there’s no ferrous metal nearby.
They’re strong enough that you can make small dents in water because of diamagnetism, or levitate graphite.
You should get some, they’re fun to play with, except when you get pinched. They’re just a bit difficult to store.
I wouldn’t guarantee this, but I recall that placing a “keeper” of magnetic material connecting the poles pretty much confines the field to the material itself. The keeper can be removed by sliding it sideways.
EASY ANSWER: ask yourself how all the magnet companies ship supermagnets via UPS or post office without erasing any videotapes in the neighboring parcels.
I’ve bought lots of magnets from wondermagnet.com. Their secret is to suspend the magnets in the middle of a thin steel box, with several inches of bubblepack-filled space between the box and the magnets. The overall magnetic field is fairly weak at that distance since the north and south poles of the magnets are close together and tend to cancel out. It might be strong enough to hurt a floppy disk, but it’s weak enough to be “shorted out” by a thin steel plate.
But if you stick your magnets DIRECTLY to the inside of the same steel box, the magnetic field goes right through the steel as if it wasn’t there. The inch or two of empty space is critical.
So, I guess you’d want to make a wooden or styrofoam box within a steel box, so your supermagnets were held a couple of inches away from the steel.
I don’t think the steel needs to be very thick. The shipping boxes from Wondermagnet look to be around 18 gauge.
Once you’ve built your box, you can test it out by putting some magnets inside and waving it near a compass or near an oscilloscope (or if you dare, wave it around your computer’s color CRT)
How about using a lead lining inside whatever material you make the box out of? You could make the lining out of lead flashing material, if it’s available in your area. It’s thin enough to work with, but probably thick enough for reasonable shielding without too much weight. And, you could always double-layer it, if you needed to.
Lead doesn’t filter out or block magnetism, Dave, pretty much the only thing that will is distance.
Personally, the idea of a wood or thin-sheetmetal box lined with a light spacer like blue construction styrofoam, and marked as “magnetic materials” is an excellent solution.
That’s not quite right, Doc Nickel. Iron (or steel) has a much greater permeability than air, and so will act as a “short circuit” for the magnetic flux.
I think distance plus a ferrous exterior sounds good. FYI the resistance that empty space or air has for magnetic flux is maybe 1000x that of iron, so you would prefer the parts to fit closely together to minimize leakage but they don’t have to be welded.
Here are some ideas about how to get a ferrous exterior container at reasonable expense and effort:
Buy a pipe nipple and two caps, in galvanized or black iron. Sizes as big as 6" (nominal, or approximate inside diameter) are available in big plumbing supply places. Home depot should have as big as, say, 3".
Buy a cookie tin or paint can. Pretty thin, though. Or get a little tool box, somewhat thicker.
Get an electrical box, the kind that surrounds the recepticals in your wall. They’re about 1/16" thick.
Now that sounds like a good solution. Get a cardboard tube, wrap it in foam or bubble wrap, stuff it inside the nipple, and there it is. Nice thick walls with high permeability, tight joints, the whole thing.
Duh. I had a bunch of pipe and caps around, I could have done that. I didn’t have time to fabricate a box out of galvanized flashing, so I left them behind (I was moving). I’ll take a pipe nipple and caps back with me this weekend.
Good spot, Napier, you win. Hopefully my brain will eventually grow back.
Not that this is my field of expertise, but something must. Since there are “magnetically shielded” speakers on the market, there must be a way to shield them.
I’ve never had a rare earth magnet to play with, but I’ve seen regular magnets’ attraction power stopped by non-magnetic materials. So, I figured a denser material would be more effective. Not so?
