This is a jig to allow you to square your model rocket's fins when you are gluing them. This jig fits a MadCow Arcas HV (2.6" diameter) but could be resized fairly easy for other rockets.

Extra feature: Rail guide. Basically, you want the rail guide to be as straight as humanly possible. This can be done with a lot of measuring, or by turning this jig on its side and (assuming your laser cutter can do straight lines) used as a jig for the rail guides.

Cut two or more on 5mm acrylic or plywood. Keep triangles handy

To center the fins: with rocket vertical, add fins with epoxy and use a third hand to hold them in place, while you fit the jig over them. add epoxy over edges to create fillets. There is a rounded edge on the jig so that you can use the jig to clean and round the fillets while the epoxy sets

To center the rail guide: assemble the standing trinagles and run the rocket through the middle of the jig, with one ijg fit to the fins and the other where you want to mark the rail guide. Mark the rail guides using the square divet in the jig on each end. I'll have pictures shortly.