You're probably tired of my repetitively sticking up for my grey savior, so I've got only a little more to say. I suspect some of you are not using the tool correctly, so while I was attaching the fins to my current build, I took a bunch of pictures in order to write this short tutorial about what some folks have been known to do wrong.
First, make sure the vertical veins are inserted the correct way around, and that you're preparing to put the fins on the right sides. The base has arrows that show which side of the veins to use, and the veins have "3/32" molded into one side and "1/8" on the other. For the picture below I put some paint into the 1/8 so it would stand out better. For any other fin thickness this is not the right tool.
Once the rocket is on the stand, push the veins up snugly against the body tube. The center post holds the rocket centered and close to vertical, but it's the veins that hold it really vertical. Check for plumb and adjust if necessary, keeping the veins against the tube. Today I used a small square to check for plumb, because I suck at eyeballing anything, but usually even I'm good enough. (In fact, even today I didn't have to adjust after I checked.)
Then put a stripe of glue on your root edge, place the fin against the vein and clamp it,
then push it up to the tube.
Yes, the veins can rock a little bit side to side, but they want to stand up straight. Check them and nudge them upright if needed. Make one last check that the veins and fins are all firm against the tube, and walk away.
Give the glue plenty of time. I use yellow wood glue, never mind which product, this isn't a glue thread. As we all know, full cure takes overnight but things can usually be gently handled in a couple of hours. For these root cord edge contacts, give it a good four hours or more.
Here's what my rocket looked like when I took ot off the jig. Perfect? No. Garbage? Far from it. Better than I'll ever do freehand and by eye on my best day.