Selecting Dry Tumbling Grit

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Selecting Dry Tumbling Grit
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Selecting Dry Tumbling Grit
Polishing or burnishing soft metal (brass,
copper, aluminum, etc.) parts with Corn Cob Grit
in either a barrel or vibratory tumbler is a
popular process. Selecting the proper grit size
for small parts or parts with complex geometry
can be a real challenge.
The initial testing used for this part (only
portion of part shown) used the same medium grit
size as is used for larger, less complex parts
also being tumbled by the customer. Due to the
size of the many slots, holes and grooves in
this part, this medium grit size media got stuck
in many areas making the cleaning process timely
and expensive. There are two options.
Brass Part
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Using a larger grit size to prevent the media
from getting stuck in the first place will
address the problem and still provide the
required burnishing action. Of course, as the
media wears and breaks down, there is an
increasing risk of media getting stuck. Using a
very fine grit will prevent the problem
completely. Unfortunately, finer media sizes
(i.e., lighter particles) can sometimes not
provide the force/work necessary to achieve the
desired surface finish. In addition, finer media
can pack into the interior areas of the part
like the inside diameter of the part pictured
making the media removal just as
difficult. There is no right answer to this
problem. Balancing the required surface finish
with the effort (time, labor, etc.) to achieve
that finish will determine the appropriate
process for each situation.
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