I was wondering if folks here could describe (or, even better...show pics) any home made rigs they've used to measure dropout alignment. I have a few bikes with frames that have had the rear triangle re-spaced and (not one of the respaced ones) an old 6 speed (rear, that is) road bike that seems to have turned up a bent rear axle, so it seems like I should have a tool to measure dropout alignment.

corollary question - would a cassette that appears to wobble slightly when the hub is freewheeling indicate a bent axle?

I think it would be a pain in the butt to make dropout alignment tools when a set only cost $80.
Here's a link to photos though.
https://www.parktool.com/repair/readhowto.asp?id=40

Answer to 2nd question is no. It is an result of the machine that cuts the threads into cast or forged parts not being perfectly parallel to the axis. Not a problem as they allow a certain mfg tolerance for this.

You can check alignment using two threaded axles. Basically you put two lock nuts on each axle, then lock them down on each dropout ( make sure they are fully pulled into the dropout). Make sure the ends of the axles are close to touching in the middle, so you can easily see the misalignment. If you need to make an adjustment, you will need a bit of tubing to slide over the axle to get more torque. Have Fun

IF you plan on using it a fair bit, replace the locknuts with wing nuts.