After two years as a BAR, I still don't reliably get fins on my LPR rockets in a reliably perfect manner, particularly when there are multiple fins in line (like main fins plus higher canard fins).
I have built bevel fin guides:
And found them good but inaccuracies in construction techniques in my hands mean that while my fins are straight with respect to the long axis of the tube, and multiple fins (main plus canards for example) are coplanar, sometimes I'm off noticeably in that the fin plane doesn't intersect with the center of the tube. Further, the way I built it, if the canard fins are far up on the rocket there's not really room to attach them. I can think of design changes to address this, but I've found I prefer a tool that lets me get all three on at once.
I've also bought and beefed up the Estes fin tool, by putting a solid 1/2" bolt in it for greater center mandrel stability:
It's a good starter tool but I'm looking for something beefier and that has better vertically-stable guides for the fins. I know that variations on the theme Estes chose are commercially available, and would probably suit me well. But, I really wanted to build something I could adapt as my needs (and whims) change.
And so, it begins.
I will document my efforts here. I think I'm about 80% complete, and just haven't had time to document things. Stay tuned, over the coming week I'll document my stuff here. Let's see how it turns out!