[MattC9]

This is a good start, when I was designing gearboxes one thing I would make sure to account for is how it would be mounted. I see two empty holes on either side of the output shaft, are these going to function as your mounting points for a face to face mount? If they do you will have trouble getting a nut or screw into the tubing because you will have a gear behind it. A good alternative might be to extend the ends of the tubing a bit and put mounting holes on the outside edge of the CIM motor. My last thought for this IF you are planning on a face mount is to use smaller screws and place them on the inside of the tubing. This will allow you to have a flat face mount without having to drill clearance holes in the chassis, except for the bearing.