I've wanted a neck jig for a while. This is the common one
Basic idea is to reproduce the neck's shape under string tension, with strings off, to enable better fret work. There's debate out there among those who love them and those who level frets in candle light with naught but a rusty spoon, but here we are. The SM one is too pricey right now with a drum sander build and other things, although I don't feel great about copying the idea.
I'm using ally extruded profile, there's a few types with their own system of fittings & widgets so you pick one and go with it. It'll be quite light and pack away to basically a stick shape that can be hung up out of the way.
So you need risers for the body, risers for the neck, and mounts for dial gauges. Also two things to act on the headstock but more of that later.
Took a while to figure out sizes and this 'n that and it's slow with a bandsaw and a drill doing it on the odd evening/spare time. Someone with a mill could shave hours off the time. Anyway here we go-
Neck risers; chunks of ally bar. Through-drilled out some tube pieces to 8mm ID. The OD is under a half inch, but by chance I have a drill bit that's undersized a hair or three, and putting the block in the oven and the riser tube in the freezer, the tube fits in if you're swift. Joy! I can use a drawbolt to pull it in as well, if it puts up a fight.
Lockdown haircut (test piece for heat/cold press fit)