A while back I saw a post where a guy jacked his car up, to polish his wheels.. Since I found that to be an easy way to die, I took the idea and ran with it.. I built a 2x4 frame table, 3'x3'.. Cut, and modified the end of a 7.5" axle, mostly for the bearing, and used a 17.5 RPM DC motor, with a variable speed control and a forward reverse switch (It was for a press, and we had it in storage.) This is what I came up with.. It looks rough, but man does it run nice.. I haven't tested it yet with the sander, I'm hoping it works good...

Do you have any videos of it working?

That's a fun/cool project, but the post subject is WAY misleading! There's nothing CNC about it. That would mean you're machining rims using a computer controlled tool... unfortunately that costs a lot more than $40 :-(

Anyway, how do you have the axle section secured to the wood frame? What kind of sander do you plan on using? What did you use as a coupler from the DC motor shaft to the axle shaft? Are those exposed wire nuts hanging? the wire looks like it's pulling on them. you might want to better secure it so they can't be pulled apart with live wires.

Looks sketchy.
Secure that (rearend) better.

And +1 to not CNC.

But I like your attitude about it and I think you are on the right path.