If you’re building model rockets you want to make sure they fly straight, and many of that is dependent on the stabilizer fins. It has long been a problem come assembly time. how can you make sure that they’re being aligned without any variation? [Rrix] discussed that one technique is to use a square to position them perfectly perpendicular to the bench on which the rocket is being assembled. but this is still prone to error. His method uses a couple of precision jigs made out of cardboard.

He developed this pair of jigs in Inkscape, then used the files to fabricate them out on a laser cutter. It worked like a charm, but led him to another issue that can be resolved in a similar way. model rockets have rail guides that travel along a rod attached to the launch pad as the craft accelerates to a point where the fins have enough effect to keep it going in a straight line. If those guides aren’t straight, your fin alignment will be all for naught. His second version of the jigs includes a cut out for these guides.