This fin jig is intended to be used as a tool to help you get the fins attached to your model rocket correctly. The jig itself will not magically get the fins aligned correctly, it will serve as a guide to get the job done. It is intended for use with body tubes that have a diameter of over 2". I have personally used it with BT80 tubes for low and mid power rockets, and 3" to 4" diameter tubes for high power rockets. If you wanted a fin alignment tool for smaller model rockets, simply reduce the dimensions and you should be fine.

How To Make A Model Rocket Fin Alignment Jig

The idea was to make this fin tool for as little money as possible. A 2' x 4' piece of particleboard was picked up at a local hardware store for under four dollars. You could also use plywood. Particleboard was selected to make it super-cheap.

The pieces were cut out using a Dremel rotary tool with a Mini Saw Attachment (Dremel #670). Obviously, you can use whatever saw/tool works for you.

Once you've cut all the pieces and sanded them smooth, you should end up with what you see in the picture on the right. The pieces, left to right, top to bottom are : two side panels, back and bottom panel, top strips and two (top and bottom) support pieces. The side panels are 12" x 24. The back and bottom panels are 9 1/2" by 12". The back panel as a section (2" x 6") cut out at the middle on the top side of the panel. The top strips are both 24" x 4" and the support pieces are 9 1/2" x 1".

Assembling The Fin Attachment Tool

The initial idea was to assembly this jig with some nails and maybe some wood glue. It became clear very quickly that nails were not the way to go for me. While I may be many things, a carpenter is not one of them. The particle board kept splitting.

Plan B was to use epoxy resin to join the particle board pieces. This, as it turns out, worked very well.

First, the top strips are attached to the side plates. I did manage to get a few nails in place to keep these pieces together. Some wood glue would probably keep the pieces together long enough, until the epoxy could be applied.

Next, set the sections you just assembled upright. Note that the pieces are actually upside down, the top strips are resting on the table. The back plate is put into place and secured with some masking tape (over the joints on the outside, not seen here). Please note that the back plate sits between the two side plates, and on top of the two top plates (while the jig is upside down, as seen in the picture).

The masking tape mentioned above will prevent epoxy from going all over the place in case it finds it way to the outside of the joint.

One of the support pieces is placed in front, as shown in the picture. As this point, epoxy fillets were applied to all the joints on the inside of the tool (and to the support strip). West System 105 epoxy resin with 206 hardener was mixed. Colloidal silica was added, a little at a time, until the consistency became peanut-butter like. The epoxy was mixed to this consistency so that the vertical joints in the back could be done at the same time, without having the epoxy run down.

You could also use 15 or 30 minute epoxy. If you don't have a filler to make it thicker, simply do the vertical joints separately and flip the jig on its side first. That way, the joints to be epoxied will lay flat.

Now, flip over the fin tool assembly, to stand it upright. Slide the bottom plate between the side panels. Slide it all the way to the back. Put the bottom support strip in place, as shown in the image. This strip will also serve as a guide when using the fin jig. Some wax paper was put on the table to ensure the epoxy wouldn't permanently attach the fin tool to the table by accident.

As you can see in the image, there is a large gap in the bottom, this is perfectly normal. This is done so that you can slide the tool partially off a table if the fins on the rocket are so large they'd extend past the bottom.

By now you're probably wondering how you use this contraption. And how exactly it will help you get those fins on straight? Read the next page for answers to those questions.

Next : Using the fin tool