update: We used emery cloth to downsize two drill rod shafts say 8" long and 2 out of 2 shafts appeared to be microscopically "bent" when installed on our shooter between 2 brand new bearings. The center of the shaft moved up and down when hand rotated even though it had never been run under power. All I can think of is the drill rod surface hardness was not consistent and the emery cloth wore down parts of the surface faster than others.
Next year we buy the correct shaft rod from McMaster Carr. And find a machinst mentor
