How To Get Straight Fins

Types of Misalignments

Fins misalign in one of three ways, or any combination of these three errors.

Solve by using a sheet of paper wrapped
around body tube. click
Solve by using Photoshop Method click
Solve by using Simple Fin Alignment Jig click

Wrong Location

In my shop, my precision making linear measurements is an order of magnitude higher than my precision making angular measurements. To convert the alignment task from angles to inches, use a sheet of paper wrapped around the body tube.

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Not Perpendicular - Photoshop method

Using a digital camera and a photograph editor permits very accurate alignment of fins. A digital image magnified in a photo editor will display tiny misalignment problems which the eye could never see. Iterating through just a 2 or 3 photos->Photoshop loops should yeild great results.

I use Adobe Photoshop, but any decent quality photograph editor should have similar features.

Corkscrew Effect

Using a single piece of wood, a simple fin alignment jig can be constructed.

The angles and dimensions of the cuts are not critical. This jig can be built in about 30 minutes. It is sufficiently simple and inexpensive that I usually make a new jig for each rocket. This fin alignment jig allows the fins to be attached to the rocket body with the top-to-bottom alignment nearly perfect. In other words, the rocket should have almost no spin when this method is used.

In addtion to top-to-bottom straightness, the fins also need to be attached perpendicular to the body tube. To get the angles accurate, see my Photoshop Method for fin angle alighment.