I want to make a couple of quick post about my tumbler which may be useful to a new tumbler builder and user.
Thinking about the steel aggregate which I use in the tumbler illustrates a point about dealing with burrs and sharp edges. I use carbon steel ball bearings and punch drops as the two main types of aggregate. The bearings are expensive and the punch drops are essentially free. I use the tumbler as the storage space for the ball bearings and some have probably been in there for years without noticeable change in appearance. The punch drops initially have a sharp burr edge which seems to disappear after several tumbler run cycles. Careful inspection reveals that the burr was folded over forming a cold shut. Actual deburring does not occur.
That doesn’t cause me any significant problem but the same thing can happen on workpieces where the cold shuts can be trouble. Moreover, it doesn’t take an actual burr to create this problem. A sharp 90º corner is pounded over into a pair of cold shuts. To avoid the issue the sharp edge should be removed by sanding or grinding to create a radius.
A little attention to detail can can prevent some annoying defects later.