The magnetic tumblers I built,were from these drawings and
instructions from Robert Christopher:
They worked great,better than the commercial tumblers I have seen.
My total parts cost on the last one was less than $250.00
I used larger magnets than Bob's plans call for. I used 1.5 in. X 1
in. thick 40 mgo magnets.I also used one of the bowls from one of the
small vibratory tumblers. By using more powerful magnets, the action
was so strong it was throwing the pins out the top of the straight
sided bowl. The curved sides and built in baffles of the vibratory
bowl give a beautiful action.
By shopping around on ebay, you can find the magnets at a good
price. The price of the magnets have come way down, since Bob
published his plans. If you do use larger, more powerful magnets,
than Bob's plans call for, be very careful. The larger magnets can
slam together almost at the speed of light, breaking fingers,or
exploding,with shrapnel like fragments. They are very brittle. Do not
handle the larger ones, without protective gloves and goggles!
The experimental tumbler I am working on now uses 2 in. X 1 in.
thick 40 mgo magnets. If two of them were permitted to come together,
I could not get them apart.
good luck, Andrew