[Richard Wallace]

Originally Posted by asid61

The boss plugs into the encoder plate though, which plugs into the gearbox. I'm not talking about changing that, just putting a bearing in the gearbox plate to make the cim not as cantaleivered.

Sorry I misunderstood your idea earlier.

So, if I am getting it correctly now, you would put a third bearing on the motor shaft, between the encoder and the pinion? Maybe a 608, with 8mm ID x 22mm OD x 7mm length. Then you'll have 31 - 9 - 7 = 15 mm left for the pinion and its retainer, so a standard 19 mm pinion would need to be cut down to about 12 mm. This will still be enough to engage a 3/8 inch (9.5 mm) gear tooth face. A little more demanding of axial gear alignment, with very tight axial clearances.

Edit: maybe leave about half of the 608's axial length protruding from the encoder adapter so it functions as a pilot for the gearbox? This would allow larger pinions (e.g., 14 tooth) to clear the pilot diameter, making gearbox assembly easier, while relieving some of the tight axial clearance problem.