I sprayed the four brackets with dyechem to help with machining the couterbores for the inside bolt head/washer/socket clearance. I made the counterbores with a 3/4" end mill. I controlled the depth by hand/eye using the dyechem to judge full clean up without removing any excess material from the floor of the part. I then set up my Lyman tumbler (for tumbling brass for reloading) with plastic media and put the fwd brackets in to deburr/final finish. We will see how that works, the parts are a little big and are resistent to "tumble" in the small bowl.
8 counterbores made on brackets
Counterbore close up. Dyechem used to help gauge depth
