Cutting fiberglass (fin)

So I just laid up 32 layers of 6oz. and 7.5oz. Volan for a heavy duty longboard skeg (10"x12" actual fin measurements)…I don’t have too much in the way of saws. What can I use to cut out the fin shape from the layup? I can borrow a saw, but do I need a special bit? I was just going to chip it out with a chisel (ok, kidding, kidding)…I suppose any special dremel bits are out of the question for a job like this? Thanks…

The grit blade that fits the common jigsaw is perfect for the job. Most grit blades are tungsten carbide.

Grit means just that, there are no teeth on the blade.


Thanks…Is this George by the way? If so, we know each other (or DID)…

Hey Tenover,

what’s up, this is he, in the virtual.

(wished profiles would show more (not too much) info) but your privacy is there to be respected, whomever you are…

Good Luck with the cut!


Sorry…Didn’t mean to give out any info. I know Chris Iacono(sp?) and we used to surf together at Avalanche and the cliffs quite a bit together. Checked out your shop a few times when you were in the back of the house…

I’d suggest a hacksaw for cutting a fin plate. I think the grit blade would heat up, melt resin and get gummed up.

Cutting a plate, though, can be real hard on a blade. Apparently fiberglass is quite abrasive. I caught an earful for using my grandfather’s bandsaw, only once. After that I learned to cut plates when they were sufficiently gelled, using a utility knife.

Hmmm…Thanks Honolulu…Wish I knew that about (looks at watch) say…20 minutes ago! So you draw your template or shape on semi-wet glass?

I have a scroll saw if you want to drive up to North county. I’ve taken stock fiberglass fins and cut them to fit into FCS plugs. It takes a while. Dulls blades reall quick. Two or three scroll blades to cut tabs into two fins.

Not sure about the blades Plus one is using but I plan on looking into that.


I may have screwed up…I laminated all the layers up with Lam resin…??? I’m wondering how I’m supposed to foil it. Isn’t it going to gum up the sander BIG time?

No. Just hotcoat the outside. It will sand just fine.

Actually, the best fin sheets seem to be from 1 part real Gloss resin to 2 parts Lam. Isothalic preferred.

This results in a better “springback” rate or crispness to the fin.

Hey Tenover! I just made my first attempt at making a couple of fiberglass fins.

I’d suggest You go and buy yourself a cheap angle grinder and fit it with a stone cutting disk.

It goes like a hot knife through butter!

Good luck


carborundum grit blades on a jigsaw … the way to go, for me !!

I have also used a grinder to cut them out . You want a respirator and goggles doing that . Plus …if the fins [two or more ] are close together when templated on the [dry , by the way] panel , the width of the grinder’s edge may accidentally cut off some of the fins outline[s] …learnt that …once !!



Those grit blades are good but really slow, if they get too hot they will snap (ouch!!)

I have recently been using toothed blades from bosch, but they have tungsten teeth, will cut any composites with ease and speed. They are expensive but outlast anything else you can find


Carbide grit blade. Expensive for band saws, cheap for jig saws. Home Depot has them. You can cut green panels with a razor knife, but you do get about a 1/8" to 3/16" delam into the cut fin edge. There is also a carbide grit hacksaw blade that is a round rod coated with grit that works well. Also at Home Depot.

Hey tenover,

When i was into making fins, I went up to the local hardware store and they had a bit for a jigsaw specifically for cutting fiberglass. No problem gumming or anything. Cut out 5 fins in a row and still sharp. Hope that helps.

Austin S.

Aloha! Carbide jigsaw blades for sure. They grind as they cut. The ones for fiberglass and tile are the same. I used to go through a lot of them, and I had a big pile of broken ones. I would clamp the blade in a vise, and grind the blade shaft so it would fit in the machine. It shortens the blade, but makes fresh grits to cut with. You can easily double the use of the blade= more cuts. I actually preferred jig saw blades over bandsaw blades for the maneverability factor. More fin blanks on a sheet, closer together. Less waste. Aloha…RH

Wow that’s cool Rick, thanks for that one!

Basically moving the “wear spot” on the blade by shortening the mounting tab, HA!

Shoots! You can’t forget the wear and tear on the saws though. I also had a stack of those things too. I finally got the clue to buy the econo Craftsman jig saw at Sears. For a few $'s more, you can get the replacement plan, so when the greasy black lubricant is draining out, and the blade shaft is flapping, you can take it back for a fresh replacement. All in all, better than burning out a stack of higher priced saws. Once, I got super serious, and ordered a Porter Cable worm drive ‘bayonet’ saw. The things are made to cut steel. The thing was so compact and powerful, but… I searched the entire U.S. and couldn’t find carbide blades that would fit it. Ended up sending it back (on my way to Sears). I think I’ve seen refurbished P.C. saws in the Harbor Freight catalog, that had a shaft that would use regular jigsaw blades. If I ever got back into the fin biz, I’d check that out. Aloha…RH

my carborundum blades cost $12aus , my saw cost $29.95 at bunnings …I’ve had 'em both for ages !!

how big is the sheet o’ fins

…got a 4’’ backing pad on the mini grinder

get a 5’’ disc,hard resinback type

cut it out w/ the mini grinder

saw basa do it with a big grinder,cut out a template when 'e dint have a jigsaw


rolling thunder in Kapaa