Some guys just add layers of cloth way thicker than needed to build up thickness for the futures canted base, then use sanding block templates to shape and angle the base. I’ve never tried to make futures rail fins. The canted bases have steered me away from their system, though I like it in many other ways, even from a Non production standpoint.
I find that when sanding fin tabs, it is far to easy to go from too tight, too tight, to too loose with just a few sanding strokes. Now when I start getting close to the right thickness with 120 grit, I switch to 220 grit wet to get it closer then quickly to 400 wet, and test fit after every few swipes. Pretty important the sanding block is truly flat, not flexible, and the sandpaper is adhered to it, and even with such precautions it is easy to go too far or have imprecise results and have to add more layers and try again.
Also test fitting itself can actually widen a fin box from repeated insertions and removals of a rough based fin, so it helps to pass some 400 wet over it just to smooth it out and make the fin base less rough so it can’t chew up the finbox’s sides as much.
I’ve been trying to use my Tablesaw for Probox fin tabs, with both excellent and poor results as my tablesaw’s fence needs so much manipulation to be parallel with the blade and fractions of a MM style precision is required. I demand a friction fit in the proboxes with the grub screws merely for retainment, not to push the fin tab down against the opposite side of the fin box.
When I have needed my epoxy to not stick to glass when making a fin panel, I’ve never used any mold releasing compound, designed as such, just using regular car wax, but many layers, lightly buffed in between once fully glazed/dry with subsequent layers applied with almost no pressure once once hazed/dry using minimal pressure to remove. This can take a while and removing the fin panel still requires forcing some razor blades under the edges of the perimeter, and perhaps some heating and cooling to pop off cleanly. I’ve taken to just pulling ziplock freezer bags flat on the glass/Mirror and taping the edges, as epoxy does not stick to it, but any seams of the bag show up, as do any wrinkles if not pulled tight, or if it is stretched when spreading the epoxy.
Note that removing the fin panel from waxed glass will take the wax with it, andcan later contaminate sandpaper or other surfaces, and lead to fisheyes/orangepeel, poor adhesion, curse fests and thrown tools. So it is wise to not do any of the waxing application or removal in the same area where future final coats will be added, and wiping any fin panels with a solvent before allowing them to touch tables or sandpaper or other tools like jigsaws their blades or powercords. All can be a future source of contamination, fisheyes and tools launched into low earth orbit. Much less an issue with PE resin but with epoxy one needs to be more aware of how easy it is to transfer contaminants.
No idea if this Plastic ‘trick’ works with PE resin. I dont use that anymore.
