Learning Fin Construction Part III: Hey! Cut It Out!

Safety first- read and follow all safety rules and instructions before using any tools and materials which may be hazardous!

Part II ended with us having an unfinished edge fin with some bonus epoxy at the bottom.
It took the wind out our the sails a bit.
The bottom was thick with epoxy, the part from the original manifold that set up too quickly to be separated from the marked edge bottom. This could not just be sanded away…at least not in this lifetime.
This called for the big guns…this called for the wet tile saw!

Wet Tile Saw- no water in the pan, but you get the idea..

The wet tile saw with the diamond blade was a miracle- it cut through the excess epoxy, and made a clean edge of the messy fiberglass/epoxy edges very easily, saving a lot of extra sanding time on the edges. As a plus, since the saw was kept wet, it prevented fiberglass dust from flying everywhere and creating a bigger mess. Unfortunately, the bad thing about the saw is that the blade is recessed so it’s hard to see where the cut is in relation to the top versus the bottom, so I had to keep flipping the fin over to make my cuts, and I still managed to overshoot in a few spots. Those small overshoots, however, I believed, could be remedied by some sanding, a little of which I certainly don’t mind.
I did do some preliminary sanding of the edges of the fin on the wheel sander, but I wanted to wait on doing the majority of the sanding after I made my rough cuts for the bottom part that will fit into the fin box.
I needed to mimic the shape that was on the pro-made fin bottom, that would hold the pin that would slide the fin into the box, plus the vertical drill hole in the front section to secure the fin by bolt into the box. Here’s the pro-made fin:

Professionally Made Fin

I traced the pro-made fin bottom’s shape onto our fin with a sharpie pen, and once again used the wet tile saw to cut those lines. This is my result after using the tile saw:

Our result
Fin with edges trimmed
Profile of our fin

Yikes- yes, the glass job looks a bit rough, but that comes with practice, I guess.
Still, I was fairly happy with the result, now, it was time to sand, sand, sand. I made sure- as I have been doing- to use nitrile gloves, breathing mask, and safety glasses. I used some 50 grit garnet to try and polish up places where I overshot on the saw. While I’m not close to being finished with sanding, I worried about having cut a little close around the edges of the fin.
Because of this, I asked my husband if we could cut strips of fiberglass to bend around the edges, like of like my bias tape I use for sewing. I even demo’d what I meant:

Bias tape???

Fortunately, he told me that pre made fiberglass tape already exists! This was great to hear since cutting strips sounded like a pain. So, we’ll be picking some of that up.
Also, we needed to prepare to drill a hole for the pin and a vertical hole in the front bottom for the bolt. The hole for the front hole seemed like it could be pretty standard, but the pin in the back was a bit unusual, so we measured it with the dial caliper to get an idea:

Using the dial caliper to measure the pin

The pin is also one of those spring types, slit down one side so you have to squeeze the tube together so it releases fully when you place it into the drill hole in order for it to hold. We cut a piece and have one ready to go, but we may need a different drill bit. I guess we could alter the pin size, but we figured that may make the fin loose or sit funny in standard boxes.
Speaking of the fin fitting….
On purpose, we did make the base just a bit larger than the pro-made fin, since it appears there is some shaping and change in measurements along the bottom, which was true for other fins we had. We assumed that this was for hold power in the fin box, not just QC problems at the fin shop. I’m opting to sand it down with the wheel sander and by hand to make sure I can get the profile.
Nexttime, however, we have already started to make a mold for the bottom that will make life easier. We can just make the fin, and stand it in the epoxy and then glass them together:

Male mold to make the female mold

For the female mold, I have some quick dry mold material that can take epoxy, so having that on hand already was great.
Now, we just need to clean up the fin, sand, sand, sand, and put some gloss coat on it.

Correction 8/13/11: I’ve been told that I’ve been using the term “dry” and “drying” with epoxy, when I should be using the word “cure”. Thanks for everyone’s help- I’ll get the lingo down someday…. I hope.

Next Section:
Part IV: Sand, Sandin’ Away….

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