Ball Turning Attachment
In the Aug/Sept 2008 issue of Machinist's Workshop Paul Holm describes the process for building a ball turning attachment.
The drawings of the base plate show a large 45 degree countersunk area with slots for two keys that match with the pivot bearing. Mr. Holm indicates that a "special bushing" was fabricated to broach the keyways.
My suspicion is that the broach bushing is that it is a little less than .876 inch diameter to fit the parts in question and that the large 45 degree countersunk area is cut after the broaching process.
Am I correct and, if not, can anyone provide any more detail on this?
Upon closer inspection of the drawings I determined that the "keyway" in the base of the tool was cut with a .125 dia. endmill. The special broach guide was sized to fit the brass beaing and required an index pin to assure that the keyways were 180 degrees apart.
Looks like the whole thing will work just fine.