Kuhn Fin Jig Set

thingiverse

The fin jig designed by Howard Kuhn has appeared in the <em>Handbook of Model Rocketry</em> for decades. I'm no good with tools, but I'm okay with a mouse and a friend with a 3-D printer. So I thought I'd make the jigs that way, using the dimensions of the common wood trim Kuhn used. There are three jigs in this set, identical except for the widths of the slot for the fin. Each is only about 4 inches (100 mm) long, suitable for smaller spacemodels. These should be good to set 3 or 4 fins (one at a time, of course) on 18 mm tube, and more fins on bigger tubes. It should also work fine for 3 fins on 13 mm tube, but there might be clearance issues for 4 fins on 13 mm tube. The dimples at the end (and the number in the filenames) indicate the width of the slot in 32nds of an inch. If you find the slots too snug for your fin material, either sand the slot a little wider (sanding evenly on each side, please!), or use the next size up, shimming either side of the fin with strips of index card as needed. CONS OF THE DESIGN: Only attach one fin at a time One jig only supports one fin thickness (which is why I felt the need to make three) Thick and Solid (a drawback in terms of volume of material used) PROS OF THE DESIGN: Secures fin straight down tube as well as straight through tube. Not dependent on tube size Not dependent on number of fins Not dependent on relative position of fins Jig design keeps it out of the gluing zone ... which is why <em>Handbook</em> author G. Harry Stine vouched for it as the best he'd seen and tested.