Rare earth magnets 2!

Twenty years ago, neodymium-iron-boron (NIB) magnets were very exotic technology indeed. They didn't hit the retail market at all until the end of 1984, and then they were seriously expensive for some time.

That was then, this is now. NIB magnets are all over the place now, in everything from electric motors to construction toys large and small

Today, you can get "surplus" NIB magnets from umpteen dealers at prices from well under one US dollar each (for button-sized ones) to $US10 or $US20 for magnets big enough to hurt you badly.

The cheapest NIBs out there are likely to be have a low "grade" number - probably something like "N35", versus the higher-than-N40 grade of more expensive magnets.

The grade of a NIB magnet doesn't actually matter much, though. Higher grade magnets can be magnetised more strongly (and probably have been) and are more difficult for another magnetic field to demagnetise. But you can't demagnetise a NIB magnet with anything less than a seriously powerful electromagnet anyway, and the actual strength difference between old-and-busted N30 grade and new-hotness N48 grade, assuming both are magnetised to their maximum strength, is in the vicinity of 25%. The difference between the commonly seen N38 and the less commonly seen N42 is little more than 5%.

So the problem with cheap surplus magnets isn't strength. It's just that they're a bit boring.

Every basic NIB magnet dealer seems to sell the same stuff. Blocks, cylinders, disks and rings, plus odd-shaped magnets scavenged from voice coil hard drives. Old curved voice coil magnets are great for generators and motors, but the regular flat-square-banana type aren't terribly exciting, and that and basic geometric primitives is all you get.

M'verygoodfriends at ForceField, for instance, stock other magnets as well as NIBs and various interesting stuff besides, but their NIB magnet range is pretty geometrically basic.

Engineered Concepts, on the other hand, have the regular shapes, plus all kinds of other weird stuff. Their Web site ain't much to look at yet, but their stock list, and low prices, make up for it. They kindly sent me a selection of their wares.