as @sleepless said, plastic is a pretty bad idea for spacers generally. the ones that I had talked about in my original post had screw throughholes that went from the motor mounting plate directly into the motor. the plastic squished over time due to the heat and pressure, and it misaligned my spur gears.
This design is a little different. the spacer bolts onto the top of the motor, and then is secured to the motor mounting plate of the drive via threaded holes. the threads in the plastic spacer would probably rip out easily and result in a destroyed motor AND gear drive.
@sleepless great work, I was thinking of doing the same, the Ant motors 63100 , finality drive combination (current build), have many of the issues you mentioned.
Long key way, making the use of a bearing not an option, 10mm step to 8mm etc etc.
I like your new version, most motors are around the 32-30mm length, I think the finality is max 28 or 26, so a 6mm spacer would be perfect.
I think three threaded holes would be fine in each section. Four looks cramped.
The machine shops that I have been contacting have either come back with quotes that are far too expensive, or will only anodize in a single colour . If everyone is okay with it, I could just make black spacers.
I do think the colours really make the builds pop though, so before I do that, I am seeing if I can have the parts machined, and then anodized in multiple colours somewhere else.
. If everyone is okay with it, I could just make black spacers.