Sport Rocketry

SPORT ROCKETRY JANUARY/FEBRUARY 2020 7 Simple Fin Jig for Thin G10 Finned Models by Dan Wolf In NAR Competition Rocketry, thin G10 material (fiberglass) is a popular fin material. It is stiff, doesn't warp like thin plywood, and can be sanded to a smooth finish without filler material. Typical G10 fin thicknesses are 0.010" for events like A payload, 0.015" for events like A Altitude, and 0.02" for events like B Streamer. Thin G10 sheets for fins can be purchased from ASP Rocketry (asp-rocketry.com). The challenge comes when attaching these fins to a body tube. Balsa fins can be attached with yellow glue. Double glue joints allow you to move and align the fins while the glue is drying. G10 fins cannot be attached this way. The most practical way is to use cyanoacrylate glue, sometimes called "super glue" or just "CA." Most hob- by stores carry the Bob Smith Industries and other brands of CA in various types. I use the "medium" version, called Insta- gap+ for attaching fins along with the Ins- ta-set accelerator. However it can get tricky holding the fin on the body tube on the fin line with one hand while spraying the ac- celerator with the other. Even if your hand eye coordination is better than mine, you still are lining up and attaching the fins by eye. Your calibrated eyeballs may be better than mine too, but if you are younger or just starting out, it can be hard to get all three fins attached perfectly straight. I ran into this when my daughters started using G10 fins for their competi- tion rockets. My solution was to develop a simple fin jig to use to attach the fins. Some of you may be aware of the late Art Rose's fin jig. I have talked to a number of NAR competitors who own one. This is a precision machine that can insure your fins are attached straight. It has also been hit or miss for availability but may be avail- able now. Search the NAR Facebook page for a post about it. The other downside of Art's jig is the cost. It is in the $400+ dol- lar range. Because of those factors I looked into a simpler and more affordable way to align and attach fins. This article describes various fin jigs I have used over the years. I started out by taking balsa or basswood sheets of various thicknesses and placing one piece of the material on top of the other so that the top piece was offset slightly more than the ra- dius of the tube. The top piece also would have a thickness of slightly less than half the diameter of the tube. As time went on, I made newer jigs with metal for the top piece so that CA could be removed when it stuck to it. I started with square bar stock Figure 1. The author's assortment of fin jigs used through the years made with balsa, steel, and stainless steel and for different body tube sizes from 13mm to 24mm. Figure 2. The body tube is secured to the fin jig with tape. Continued on page 11.

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