Fin Alignment

You draw a line down a body tube where a fin should go. When you glue the fin on, assuming it's not a TTW, do you align the middle of the fin down the line, or do you align the edge of the fin down the line?

Edge. Just keep it consistent. Always use the same edge of the fin for consistency.

Edge.

I've found through trial and error that it is impossible for me to align a fin by trying to go center. Personally, looking forward, my fins are offset in a clockwise manner. I also take care to make sure that the engine hook is also offset in the same manner (and aligned with the launch lugs). This keeps it out of the way of the igniter leads when I'm out launching.

I wish that manufacturers would include the tip (align using the edge) in their beginner's rockets. My early rockets would have looked that much better.

I've always used the centerline. For flat fins, the edge works, but if your fins have a profile, the edge isn't a straight line.

A radial guide is useful for spacing and keeping the fins at right angles, but doesn't help (much) with alignment along the tube axis. In fact, it can make things worse because it's more likely to put give all fins the same cant, introducing a strong roll.

For model rockets with flat fins, something like the Estes fin jig is probably the best bet all around.

I have always used the center, but in the last year or so I am learning to use the edge. I can see where it makes better sense...