After many attempts with router, dremel, freehand and all sorts of jigs I nervously tried an end mill in the drill press. No need fo a milling machine, and with great care it worked nice.

Still have all my fingers (well, the 9 .75 that I had before this task anyway......)



The slots are not essential but I guess it does really help with retention, and somewhere for sand to go never hurts.

Big Al said..
I thought the slot box was ever so slightly thinner that the US Box in width.....? I had to shave down a couple of JP fins, well worth the hassle I reckon.

AB...

Should be the same, of course variations exist even in Sb fins