Magnetic Tumblers and Magnetic Stirrers

Q: What’s the difference between a magnetic tumbler and a magnetic stirrer?

A: A magnetic stirrer uses a single magnet rotating under the center of the stirrer’s top plate. It’s oriented with side-to-side poles, and the stir rod is also a magnet with end-to-end poles, so it will want to stay oriented with the magnet in the stirrer. As the stirrer’s magnet is rotated around its center (think of the arrow on a compass, made to spin) the stirring bar follows suit. They are not necessarily very strong magnets, but since there is a pair of them interacting, they get the job done.

The magnetic tumbler on the other hand, spins a disk to which are mounted, along the periphery, two or more very strong magnets. These are capable of dragging along the stainless steel pins in the bowl above. The magnets need to be much stronger, since the pins themselves are not magnetized, and there’s a fair mass of metal (the pins, plus pieces) to be moved along. The magnets used are usually disks, often ¾ to an inch in diameter, with the magnetic poles on the flat faces, so the lines of force radiate up from the magnet in a way that causes the pins to also stand on end as the magnet passes under. At least, that’s how they’re set up on the tumber I have, a Swest “mini”, which isn’t so small. I don’t know who actually built it. It works well though.

My personal choice for your situation would be to go with air—acetylene, however, You can get either the somewhat larger B size tanks, which will last for a very long time, or the smaller R (I think that’s it) sized tanks, and hook this up to a Smiths Handi Heat, a Prestolite, or some similar air-acetylene torch, and you’ll have few limits on what you can do. With larger tips, these can melt significant amounts of silver, and with smaller ones, do fine wire soldering. While acetylene means storing another tank, like propane, it’s a low pressure tank without the high pressure dangers of an oxygen tank, and in case of a leak, it dissipates very rapidly, unlike the much more dangerous (in my opinion, at least) propane, which is heavier than air and tends to pool in low areas indoors.

by Peter W. Rowe M.F.A., G.G.