Estes Black Brant XII, Kit # 9723 Build, Part 5, Decisions, Decisions

You can glue a curve in the root edges of the laminated fins. If all the root edges are flat, there will be a small gap on both sides of the root edge joints. These fins are thick and a flat root edge won't "hug" the curvature of a body tube.

   

Here's how the fin fits against the lowest section when the root edge three layers are squared up.

To fill the gap the instructions recommend a glue fillet after the fins are glued in place.

Here's after I compensated for the curve of the tube. The fit is better, a smaller root edge gap below (left of) the molded ring.

On some sounding rockets (see below), there is a small gap where the fins root edge is bolted onto the rocket body. 

You can get a stronger tighter joint, but it's tricky to do -

Glue the layers up so the center tabbed piece is very slightly recessed, out from a regular flat root edge.

I wouldn't try this unless you have patience.

Don't laminate the fins until you read tomorrow's post . . . 

Here's a picture of the real BB XII from the old Meatball rocketry website.

Notice the gap where the root edge is bolted onto the rocket body.