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What is the best source for rare earth magnets for miniatures? Is there also a guide anywhere that gives an idea on how much weight the various sizes can hold? I'm going to be magnetizing my first model soon and it's quite big and heavy. Thanks in advance.

For the US I've seen K&J Magnetics referenced frequently for supply. With regard to carrying capacity, rqare earth magnets are rather powerful, but there is a limit. For an individual magnet, pretty much any infantry scale piece could be supported. For large models, then you need to be a bit of a structural engineer and work out how exactly the weight of the supported piece will be brought back down to the base. The magnets work best in direct pull, but are also usually pretty good at lateral shear as well. The larger the piece and the further from the magnet the centre of gravity is, the more likely you will need to combine magnets with pinning or use multiple magnets. Basically play about a bit with different methods and see what works best. Individual magnets are pretty cheap, and as long as you do some trial fits before gluing in solidly, you can do a few trial runs. Just make sure you keep in mind the magnet polarity at all times, however

I second K&J Magnetics. Super fast shipping, cheap as heck, and they've never screwed up an order of mine. They have a great selection of not just disc magnets in different sizes thicknesses and whatnot but also ball bearing magnets and other stuff.

One more for K&J. Pretty much if they don't have what you need, you probably didn't really need it in the first place.

If you'll only ever need a few, it may be worth paying the premium that craft store/hobby suppliers (GF9, etc.)/Ebay sellers frequently charge, as it would be the lower total cost to complete the project. For quantities higher than a dozen, though, K&J is my recommendation. Ridiculously large selection (although most are useless for the hobbyist, they've still got everything you might possibly want), decent prices (that get better, the more you buy), and reasonable shipping. Be sure to check out their clearance/overstock page, too - if you happen to come across something useful, you'll never get it cheaper. Got 100 of my preferred size, once, bought and shipped for less than the list price of the magnets, alone.

As Flinty says, magnetization is mostly about trial and error. You can find out the pull strength of a given size/grade magnet, but that isn't going to translate cleanly into "can it hold this arm in place." A lot of people simply use the biggest magnet they can fit into any given joint, and that will frequently do the trick. Personally, I prefer to use smaller magnets (I always countersink them, too, allowing for thicker magnets with greater pull to be used), adding more at key points if I need additional hold. For things like projecting limbs, torque becomes an issue, so I would use a pin (glued on one side only, obviously) to bear the weight, with a magnet to keep the part from popping off. Two pins, in extreme cases, can stop a part from rotating where even several magnets might fail.

As for size, shape, and grade, there's a lot of variety in people's personal preference. I've seen a number of folks on Dakka that use very thin, surface-mounted square magnets for weapon swaps done at the wrist, where I might countersink thicker disks, instead. 1/8"x1/16" disks are my go-to size (small enough for anything thicker than a dainty wrist on troops, while strong enough for vehicle parts, if multiplied when necessary), but I also snagged some 1/4"x3/32" disks for big jobs (haven't actually needed them, yet). All are grade N42, which is pretty much standard. N52 (stronger pull) is also available, but slightly more expensive and the increased usefulness is debatable.

To echo Flinty, once again, double- and triple-check your polarity before you commit! It's easy to do on one-off projects (I use a stack of magnets as a handle, of sorts, which also keeps them all aligned in the proper direction, once oriented to the already mounted magnet), but magnetizing a whole squad for interchangeability (like the arms for regular/CC termies) requires a bit more care, as you need to manage polarity between like parts across models, not just sides of single joints.

[edit:]

helotaxi wrote:
Pretty much if they don't have what you need, you probably didn't really need it in the first place it doesn't exist.

Fixed that for you.

This place gives 'pull' values to all its magnets but I don't know if the values are universal:
http://www.first4magnets.com/crafts--model-makers-133-c.asp

Not sure what the shipping is like to the US but back2baseix have some great prices and free shipping for Aussies (if you use their ebay account).

http://www.back2base-ix.com/index.php?_a=viewProd&productId=74