It's pretty easy to check the fit of all the tapers in a Powerbox fin system.
Simply get a bar of bath tub soap, rub the bar of soap on all surfaces of the fin head
that fit into the fin box. When you are finished rubbing the soap on the fin head, the soap will look dull and whitish/grayish.
Install your fin in the finbox in your board and tighten the fin screw normally. (It does not require any extra torque on the screw as you want to duplicate the conditions that you will normally get when you install your fin.
Remove the fin screw, and knock the fin back a little to separate the "draw" of the tapers.
Now look carefully at your fin head.
All of the places that are in contact between the fin head and the fin box will now be shiny and darker.
Take a single cut file and work off the high spots.
Redo the soap and put the fin back in the box as before.
Install the screw normally.
Remove the screw and knock the fin out of the box.
If you have filed the fin correctly, you should begin to see the high spots spreading out.
If it's a sharp edge or protrusion on the fin or in the fin box, file off the sharp edge or protruding lump/seam until it blends in with the surrounding tapers.
Continue to gently work the high spots out until you have as near 100% contact between the fin head and fin box as you can achieve.
If you find a low spot, it's better to take a filled or thickened epoxy paste (like Marine Tex
or JB Weld (Quick) and smooth on a few thin layers of the filler to until it blends in with the surrounding fin head/fin box materials.
Be careful working anything in the fin box, as it's very difficult to file or shape down inside the fin box. Better to do your "filling" on the exterior tapers of the fin head so they are easy to "work back".
Pay particular attention to the two large flat tapers on the sides of the Powerbox fin head.
These are the ones that provide all the support for the fin.
Also look at the front and rear edges to ensure that they are not preventing the larger tapered surfaces from engaging fully.
You will know when your fin fits correctly.
It will not "fall out" of the fin box without some knocking or tapping with a soft hammer as the "draw" of the tapers will hold the fin in place even without the screw even being installed.
Hope this helps,
Last edited by Roger; 7th October 2009 at 09:57 AM.