I got a little frustrated with my redstone, the fin guide seems to be just a hair off. didn't notice of course until i had 2 fins glued on at 180d - NOT. grrr.. looked for a fin jig online. Mostly too big, too much trouble, too expensive, or not thought out well. So I took a bit to think about it and designed a quasi-universal fin jig in tinkercad. Designed to fit into an 18mm motor mount, with sleeves for 24 and 29mm. Should work on anything up to a BT-60 I'm sure it will need some tweaking after the first print, but looks good. There's probably lots to know about springy plastic, tolerances, print head size, and a bunch of other stuff. Now I just need to find a friend with a 3d printer to make it for me to see if it actually works.