I was at a plastics manufacturer (per advice of others) looking for lexan to make a few fins. The guy was selling lexan for $177 a sheet. I only needed a few square feet so he said he would sell me srap pieces alot cheaper. so we went back to the back room looking for scrap. We came to a pile labeled Lexan and he started pulling stuff out. My eyes wandered a little and I read a tag that said “Fiberglass Reinforced Lexan”. I told him I wanted that stuff. I bought $45 worth (25 - 30 fins) and I did a test fin at home. the stuff cuts easily on a band saw and sands easy too. It has a much better breakage rate than regular Lexan and not nearly as flimsy. Only 1 downside, I havnt figured out how to make it clear yet. my test fin is cloudy but does have a really bitchin effect w/ the flames I sharpied on to it. the fiberglass reinforcement is layered in with the Lexan if you were wondering. Its not encased in fiberglass. And, it doesnt need to be sealed or glassed, just cut and sand, thats it. Its cuts easily with a number 14 tooth on a band saw, and 80 grit on a mounted belt sander. then use 110 and 220 for final hand sanding. I am buying a blow torch and I will test that out to see if it unclouds or not. Ill post pics when I get back from work.
Another word o the fins strength. I am no math genius or expert on tensile strength and that stuff, so here was my low tech “breakage test” for this fin material. I made a fin, sanded it, than finished it off. for testing, I finely measured wind speed using lick the finger method, then chucked it at the brick side of my house like a boomerang. it just bounced off the wall and nearly hit me back in the head. the only damage was a minor ding on the tab. no cracks or breaks or chips. The stuff just dents.
how did you go with the tabs …are they single finbox or fcs or other type tabs ?
ben
a “lexan boomerang” …now there’s a thought , if you don’t like them as fins !!
Glass reinforced plastics can be plenty strong/stiff enough for fins, but they are not made for machining/shaping. They are good for putting in casting molds, though.
I’m still wondering what is wrong with glass for fins. You can make a fiberglass fin clear or opaque or colored or multicolored, and it is stiff and strong enough and foils easily. The only valid reasons I’ve heard for any other material are
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Wood. Aesthetic beauty and/or weight
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plastics. Cheap and can be made strong enough with glass reinforcement - but only done in molds.
I’ve made fins from plastic (not from molds), from stock matted glass, from laid-up glass stacks, and from wood. The glass fins are the easiest and fastest to make, also. It just takes a little practice.
reason i dont use fiberglass is cuz im an ubernewbie with glass. that and the plastic was cheap. as far as the mold thing goes, the guy i bought this stuff from sold it in sheets. he just said cut it and sand it. I had no problem machining it at all. if someone else knows of this product, can you please post any problems it has that I havn’t uncoverd yet. heres a diagram of the sheet:
---------------------- < plastic
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this is where I got it from… check out these amazing products. also, according to them, my fin is bullet proof. (time for some secret agent surfing). Also, the stuff I used is waht you find at banks (the really thick plastic shield).
my tabs are FCS. i could probably make them for boxes easily though.
were they the right thickness for fcs tabs ?
Or did you have to file down the thickness ?
Three fcs tabbed fins ?
Please post a photo when they’re all done eh Scott…I reckon three lexan fins on an fcs plugged thruster should look god [and hopefully go well !]
cheers !
ben
I’d give that a try one day , if I can find a supply…
the sheets i bought came in 1/4" thickness (exact size for FCS double tabbed fins) the stuff isnt perfectly clear when done (still figuring that out) but has a cool ghosty effect to them specially when u use sharpie on them. also, sharpie adheres well to it after you sand it. and yes, there goin on my 7’0" thruster. BTW… took me like 15 mins per fin including doodling on them w/ markers. ill post pics when i get off work… 7 hours from now.
heres the test fin:
and… a random pic of me in a Haz Mat suit (for the ladies)
“for testing, I finely measured wind speed using lick the finger method, then chucked it at the brick side of my house like a boomerang. it just bounced off the wall and nearly hit me back in the head.”
I’m all for scientific method… THAT’S good! LOL!
Sometimes the simplest test go far beyond expert testing. and its fun. Im still amazed that it stood up to that. I threw that fin REALLY hard and it didnt break (rocks under water are childs play compared to a brick wall). i think ill make a dummy fin and just keep punishing it till it breaks.
Glass reinforced plastics can be plenty strong/stiff enough for fins, but they are not made for machining/shaping. They are good for putting in casting molds, though.
Blakestah- Outside of the surfboard world, glass reinforced plactics are machined regularly (the company I work for does this everyday). We machine glass filled PTFE, nylon, and many other engineering plastics for various non-surfing industrial uses. I think the main reason that composites are injection molded in the “fin world” is to reduce labor, increase hourly production and for the sake of consistency in the finished product (as opposed to hand-foiled fins which often show inconsistencies between two identical models).
Take my words with a grain of salt as I am only a hobbyist when it comes to making surfboards… =)
Wow that’s some gettup maybe you’re using too many chemicals in that hot tub of yours ! You should just need boardies !
Steve
I’ve machined glass reinforced plastics, too. But its a pain. It heats up easily, and eats bits for lunch.
That Get up was from 2 projets i was doin at same time. I was re-painting a car and sanding my laminate (fiberglass everywhere and paint particles… both toxic)
I just use a bench mounted belt sander w/ an air hose attachment that you see on some saws, it has flexible head that sprays air on the plastic to keep it cool. but ya, i tried to sand it at first w/o the air and it heats up rather quickly. as far as bits, what bits? i used band saw then took it straight to sander after making a few pencil marks for reference.
You should be able to polish out the polycarbonate with finer grades of compound,
for a final polish some recommend using toothpaste.
Polycarbonate does paint well, some of the local custom boat builders use it for hatches,
usually in 1/2" or 3/4" thickness, and paint it after a 240 grit sanding.
hope that helps,
Pete
Pretty sure polycarb/acrylic sheets come colored
in various thickness, may solve the smoky look,
l’ve got some 5mm matt acrylic at home that
l’ll be trying for fins when l finish my fish
(about Nov. the way l’m going) so l’ll report then
Good stuff Scott!
I put my Acrylic fcs tabbed fin in a vice really tight and tried to break the tabs. No luck. So they shouldn’t snap too easily.
I think you need pure plastic (not as strong) to get a clear fin. I sometimes draw on mine with posca too.
The plastics do come in other colours and if you look around some industrial bins they may even throughout scraps.
Post some more pics if you get the chance!
