[Al Fielder]

To get a .0002-.0005 press fit, you have to measure the actual shaft diameters as they vary from motor to motor. The actuals on the motors we had were somewhere around the .197 (inch) diameter but varied within .0005. We also found that two of our motors had slightly damaged shafts from where the pinion was pressed improperly. We then had a local machine shop make the parts. Two machining methods will work quite well; jig grinding or honing. A reamer is not as consistent as you would think.

To press a new gear on, you would need to support the shaft at the back of the rotor and then press axially so that no force is directed into the stationary portions of the motor. A good arbor press is valuable. A higher quality vise would also work (where the jaws maintain a decent parallelism under load). Always have at least a second set of hands helping while doing this unless you develop some ingenious tooling. Red Loctite is also a good idea (not in lieu of the press fit but to augment it), but as most people will warn you about Loctite, cleanliness of the surfaces prior to applying the Loctite is critical.

Good Luck