Fins are in!
I had some time last night, so I was able to epoxy in my fins. Here's how I usually set up for fin insertion.
I use JB Weld for the root attachment to the motor mount tube since it doesn't run as much as my other epoxy, Rocketpoxy, and it is a good higher-temp epoxy.
Everything is measured and numbered. Before insertion, each fin is numbered and measured for insertion into a correspondingly numbered fin slot. I use a caliper to check depth to the motor mount tube. All four fin slots were 50.5 mm +/- 0.25 mm from outer frame to the surface of the motor mount tube. I couldn't ask for a more centered tube there. All the fins were then checked for depth from the tip of the fin to 7" down (the planned fin span) and then 50.5 mm to the root to contact the motor mount. A couple fins needed ~1 mm sanded down for a perfect fin.
Since my fins are 0.5" inches thick, I had enough room to reach in with a craft stick to directly apply the JB Weld to the motor mount tube. Normally, I have to use the "double butter" technique where I put epoxy on the fin root, insert to put the JB Weld on to the tube, remove, and repeat; doubling up the buttering of epoxy. Here, you can see the JB Weld generously applied directly to the tube. Also (not seen) since the centering rings are exactly spaced at the leading and trailing edges of the fin slot, I put JB Weld on those as well since they will be in contact with the fins.
After buttering up the motor mount tube, I applied a generous layer of JB Weld to the fin roots.
The fins were inserted and temporarily held in place with duct tape until all four were in and ready for the fin guide to hold them in place overnight.
Since I use foam board for my fin guide, I cut the template span so that it's a tight fit and has to compress the foam very slightly to fit. This gives a tight fit that holds the fins pressed firmly against the motor mount tube. And since the template slots are cut to the exact width needed, the template can't wiggle or rotate at all; keeping the fins all perpendicular to the body without any eyeball aligning or guess work.
This morning, after a 12 hour cure, I pulled off the fin guide and checked the fins. They're all straight and tight with no wiggle.
Now I have to decide. Do I put Rocketpoxy for the internal filets? Or to I put in foam? With a 12" fin root, I'm concerned about getting a good internal filet without having to add a boatload of epoxy (and weight).
Anyone ever had good results putting in Rocketpoxy on such a large internal filet and getting it to run down the length without adding a ton?