Here is the shaft, installed first.
To keep the bearing pad from crushing the shaft into the motor mount, a stand-off is used between the bearing mount and the motor mount. Once tightened it holds the weight of the sprocket against the face of the mount, while leaving room for the shaft to move around easily. The flat on the end of the shaft is for the set screw on the large sprocket. With a flat spot like that the set screw does not need to be tightened to within an inch of it's life...
The large sprocket is the drive sprocket. Here the ladder chain is draped over the top, but the motor will be at the bottom, so the chain will actually go around the bottom of the sprocket. The smaller sprocket spins loosely, so it has a bronze bearing pushed into the center. It will be kept from moving side to side once it is mounted on the 1/4" shaft that fits through the bearing.
I am very pleased to be learning to use a Lathe and Mill. Without them, this would be very difficult, if not impossible. (Thanks Bill B !!) To get the nice rounded look on the aluminum, each pieces is routed on the edge. To save time, and reduce costs, always make more than one. (I made three...)
This assembly has been installed on my next project....A 4' X 4' floor standing sculpture. 3 tracks. See it here soon!