Similar But Different
Centrifugal barrel finishing machines, or 1-larperizers, are similar in purpose to conventional barrel tumbling machines. Many of the same products can be deburred, radiused, or polished in either type of machine. But the operating principle of the Harperizer (made by Harper Buffing Machine Co. in East Hartford, Connecticut) differs significantly from that of conventional tumbling units.
In a Harperizer, two or more drums, or barrels, are mounted in a rotating turret (see photo and accompanying sketch). The turret rotates in one direction while the drums rotate in the opposite direction. The rotation of the drums causes the parts (the reeds) and the finishing media to interact; the retrograde motion of the drums produces a very smooth action within the drums.
The high centrifugal forces (up to 300s in certain applications) cause a small abrasive particle to do a relatively large amount of work. It was this high-energy potential that led Delco engineers to believe that Harperizing might be the solution to the problems encountered in radiusing the center hole in the R-4 reed.
After a series of tests at Harper's plant, Delco took delivery of an 18" Harperizer (two drums, each 18" long x 18" diameter). A series of tests showed the optimum cycle finishing to be 5 hours at 10 gs to radius the reed and 30 mm at 3 gs to polish it. That's quite a reduction from 90 to 96 hours!