I'm using a rotary tumbler with stainless shot to
workharden gold wire earrings after buffing. I've tried running it
everywhere from 5 hours to 24 hours. Does anyone know what the
optimal amount of time is to accomplish this? Thanks in advance.
One of the things to keep in mind with ALL work hardening with a
tumbler is that it's not really hardening most of the metal at all.
It only hardens to the degree that it can burnish, and thus distort,
the metal. On soft metals like sterling, I'd guess you get this
burnishing to about a quarter, maybe a half millimeter, is some
cases. harder metals, like gold, won't be worked as deeply. Thus
most of the wire remains as soft as ever. Only the skin has been
compressed and burnished and work hardened,. This certainly is
better than nothing, but it won't harden the posts as much as if you
grab them in pliers before you tumble them, and give them, say, a
quarter twist. Twisting doesn't change the dimensions of the post,
but it distorts and works metal crystals, thus work hardening the
wire all the way through. NOW tumble it, to remove any residual
spiral marks from the twist, and you'll have a decently hardened wire
all the way through, with a considerably harder and more
wear/scratch resistant skin on the wire. As to times, it depends
much on your brand of tumble. You can test it with castings or fully
annealed shapes that have sharp edges and corners. Time how long it
takes to round over and burnish those details (you'll need a loupe to
see it clearly), and then how much longer you can run it and still
see periodic additonal depth to the working. If it reaches a point
where additioanl working is not making those sharp corners rounder
and softer still, then you'll know you'v hardened the metal to the
most your tumbler will do.
And I'd experiment with tumbling them before buffing (though after
perhaps, coarse cut down operations, so what goes in the tumbler no
longer has file marks, coarse features, and the like). the reason is
that generally, rouge will give you a higher gloss than steel shot.
Tumbling after you polish may be wasting some of the effort you spent