Have two new boards, 2+1 shortboard and a 2+1 longboard, each from a different shaper and glassed in their respective shops.
I’ve picked up several primary fins from two different fin companies, and have had to sand the side bases of each one to get them to slide even reluctantly within the box of either board.
What’s up with this…?
I suspect that the ‘‘problem’’ is with the dimension of the fins, not with the fin box. I have used the FU (Bahne) fin boxes since 1969. (do the math) I have NOT encountered that problem with fins that THEY PRODUCED. As you found out, you can correct the base, to fit the box. Perhaps you should consider the purchase of their fins. They have a considerable selection to choose from. I do not have any benefit in ‘‘bragging’’ on their product, I’m reporting to you my decades long experience with it. I just purchased some custom fins, and boxes last week. I’m STILL a happy customer!
Sometimes when the boards are sanded a “lip” will form inside the box. Take a knife or razor blade and try and clean it up. I have found way more fins that have to be “shimmed” than sanded, “normal stuff”.
Several of the companies that make fins to “fit” F.U. don’t mill the taper in the base that a real F.U. has.
The taper is designed so the fin fits tighter that deeper into the box it goes.
There’s always Home Depot! Baltic Birch Handy panels are perfect for making your own fins just the way you want them… no problem fitting a custom home-made fin in a box if YOU make it!
I would rather have the fins “super tight” that require a little sanding than loose and wobbly from the get go. I hate loose fins that you have to shim.