To finish my silver pieces I’m using 5/32 OVAL stainless stell shots
w/Rio burnishing compound in a small rotary tumbler, I’m happy with
the results on some of the stuff, but that doesn’t work so good on
pieces with somehow a flat surface. My pendents and buckle are
getting a “orange peel” kind of finish. Is anything I can do for fix
the problem, I’m sure I’m not the only one that as experience this,
but been pretty new to using a tumbler I’ll love an advise from
somebody with more experience.
The steel shot is hammering itself on to the parts and leaving small
dents, your pieces banging into each other and leaving small dents
or your castings have porosity which is collapsing under the
burnishing action of the shot.
If it’s porosity, it’s a separate issue.
If it’s caused by the steel shot, slow the tumbler down and make
sure you have enough liquid.
If it’s the pieces banging, slow the tumbler down, remove some
pieces and make sure you have enough liquid. Too small of a tumbler
can present problems if the pieces are large as well. The burnishing
action takes place as the pieces and shot slide down the front of
the rotating mass, if the pieces are too large for the tumbler, the
don’t really slide, they get tossed like clothes in a spin dryer and
go bang, bang, bang.
Flat surfaces are probably the most difficult thing to do in a mass
finishing system, Flat surfaces rarely work really well in tumble
burnishing. What you are seeing is impingement, this is from both the
shot and the workpieces banging against the other workpieces. You can
slow down the tumbler if you have that option but all that will
really do is slow down the process of impingement and burnishing. It
is possible to find a speed/ energy that will give a minimum
impingement but it will still be visible on flat surfaces. Flats are
best finished on the buffing motor.
James Binnion @James_Binnion
James Binnion Metal Arts