Rare Earth Magnets???

[Dave Crabbs]

Hi All,
I am in the process of making a stereo cabinet for my brother.The design is to have open shelves on the top half for the stereo equipment and the bottom half will have drawers to hold DVDs and Cd's that will be hidden behind 2 doors. The cabinet is 60" tall by 22" wide and 20" deep made from Burr Oak from a tree my parents had cut down years ago. I would like to use 1/4" diameter by 1/10" thick rare earth magnets to help hold the doors closed. I was planing to use 2 magnets and metal cups top and bottom for each door (total of 4 magnets altogether) When I got them there was a warning tag that said not to use them near stereo equipment. Could I still use them because the stereo equipment will be about 2 " above them with a 3/4" thick shelf separating them? Also could the magnets do any damage to the DVDs and Cd's that will be in the drawers next to the magnets?

Thanks,
Dave

[John Hart]

Nope...no harm at all. That warning is applicable to magnetic media like tapes and stuff. CDs and DVDs are not affected by magnetism in any way. The electronics won't be affected either. Just keep your VHS, Cassettes and 8-Track tapes away from the magnets.

...did I say 8-tracks?

[John Miliunas]

Dave, yeah I concur with what John H. said. No probs as long as you keep magnetic media away from them AND, as long as you don't have a CRT type TV or monitor in close proximity, either. (Did he really say "8-track"????

[scott spencer]

Keep them away from tapes, CRT's, TV's, etc and you should be fine. I've played around with some of the 3/4" ones, and I can stand one on edge and get it turn and wobble while holding another one from over 12" away....pretty cool little buggers! I've put 'em in a plastic bag and thrown it against a steel door from over 15' away and they stick! My kids accidently broke one in a couple of pieces....one piece is just an 1/8" sliver, but it's got enough strength to hold my DP key to a vertical face on the DP while it's running. They're amazing little magnets, and a pretty inexpensive toy if you ask me! Love those things...

[Doug Shepard]

Dave
Just my $0.02. Before you commit yourself to going with that approach, try it out on some scrap to see if you get the holding power you're looking for. I was going to do something similar a few years ago and ended up abondoning it after trying it out on scrap and being somewhat disappointed. I was planning on using them on one edge of much smaller doors (about 12" x 12"). I was leaving the mags about 1/8" below the surface and plugging, but even after doubling up and using 2 mags in each mating hole - for a total of 4 - I was just barely able to get any attractive holding power.
I like the idea of these hidden holds, and still want to use them at some point. They're just not as strong as everything I'd read - even with the added cups. I think next time I'm going to try larger diam. mags and see what happens.

[Jim Becker]

Keep them away from your watch, too...if you know what I mean...rare earth magnets are very strong and can bend delicate ferros metal parts inside such things!

[Ken Fitzgerald]

Dave...I have had the opportunity to use rare earth magnets at work to hold ethernet hubs to a metal chassis. Worked well except.......buy the magnets and before you use them on the finished project ...try them on a suitable scraps. At work we ended up not needing the magnets and I put them on one of those steel paper towl dispensers. You should have seen several of the guys struggling to get them off! You may find them to have a little more holding power than you need.

[Jon Toebbe]

They're just not as strong as everything I'd read - even with the added cups.

I don't think the cups really add anything to the magnets' strength. Iron in a wound solenoid will definitely amplify the field, but ferrous materials surrounding a permanent magnet should have only marginal additional effect.

My physics students love playing with these things. You can build a pretty impressive electric motor with a few of them and some copper wire. Be careful when one breaks though -- those little ceramic shards are unpleasant to remove when they become embedded in your fingers. DAMHIKT.

[Alan Turner]

Related to the magnets, but not to your question, I use a 1" one just stuck to my drill press column, and on it always resides the chuck key. Never has fallen, and always handy.

[Doug Shepard]

I don't think the cups really add anything to the magnets' strength. Iron in a wound solenoid will definitely amplify the field, but ferrous materials surrounding a permanent magnet should have only marginal additional effect.

Mag to Mag, or Mag to metal, these things are incredibly strong. I just ended up trying the cups as I'd heard they increased the strength. With a thin layer of wood in between the mags, it's suprising how much the strength is decreased. I was just looking for any extra oomph I could get, and still couldn't get what I considered acceptable pull (at least with the 1/4" mags) for hidden catches.

[Jon Toebbe]

With a thin layer of wood in between the mags, it's suprising how much the strength is decreased.

Your comment got me thinking, and sure enough, there's a good reason for your experience. Magnetic fields tend to become weaker as a function of distance from the source very quickly.

For the mathematically inclined: the magnitude of the magnetic field, B goes roughly as 1/r^3 (where r is the distance from the magnet).

In English: if you double the distance between a pair of magnets, you'll feel 1/8 the original attraction. Even a very thin layer of wood will cause a big drop in the magnets' ability to stick to each other.

Hmm... this gives me an idea for a simple lab experiment for my physics class. Thanks! (Man, oh man, am I ever a nerd...)

[Kelly C. Hanna]

Dave, I'd do some online research before using them. If they didn't say don't use them around magnetic media, that would be one thing, but sensitive stereo equipment is a whole 'nother ball game.