I think it's great, too. I think your adjustment screw behind the fence is a particularly good idea--allowing for precise adjustments. Frankly, that might not have occurred to me. (Sadly, there are SOOOOO many things that never occur to me until someone else shows them to me. Oh well...) But even that could vibrate and wander off-setting in use. Do you clamp the end nearest the sanding drum? Beyond some means of fixing it at any dialed-in setting, I can't think of a way to improve this jig.

That's a great jig idea! I'm for sure going to copy this. I have the commercial version that goes in your drill press, and it is very useful, but there are two big downsides to using the drill press. First, the spindle does not oscillate, which can lead to sanding scratches that don't go away easily, as well as prematurely worn sanding sleeves. Second, the drive mechanism is really in the way for some tasks. This jig solves both of those problems. Well done!

I do have two suggestions for the jig:

1. That particular spindle sander has a miter slot. You could install a slot runner in the bottom of the jig and this would help it not move around on you. Better yet, use one of those nifty slot runners that expands its width via an access hole through the top of the jig. It will really stay put.

2. The commercial version has two anchor bolts for the fence, one just like this, but the other on top of a curved slot so you can adjust the fence. A quick pass with a router on a circle cutter can make that slot in this jig in a jiffy; the first hole can be the rotation point. Flip the jig over, use a larger router bit to cut a trench for the nut that lives underneath.

I'm looking forward to building one!