thermoforming lexan

hey guys,
im new to the board but have been reading some posts, im interested in building a hollow lexan surfboard over the summer and have been trying to learn as much as i can. i love glass bottom boats and i guess that kinda inspired me to make a see through surfboard so i can see stuff while i surf, i thought it would be pretty rad. so my main question is about thermoforming lexan polycarbonate. i'd like to make the entire board out of lexan. i was reading about the softening point of lexan and with a heat gun i think i could locally make pieces of the lexan softer to form to a mold that i would place the lexan over. I was wondering if this is not true or if this heating method would introduce bubbles or any knowledge you guys had about inexpensive thermoforming of lexan would be awesome. thanks so much for any input you have.

 

hm...so i'm beginnging to think its impossible to thermoform lexan in multidimensional bends w/ a heat gun...too many difficulties...how about acrylic? it doesnt have the bubbling water deal and its easier to thermoform...but i guess the problem is that the surfboard is multidemnsional so i'd need like an oven w/ the mold of the surfboard...i dont get why i cant just locally heat areas w/ a heat gun to a sufficient temperature and have that area form to the mold? sorry..just trying to be clear..thanks again for the help

 

You can form lexan, but I've always seen it done with the blank heated in an oven to get the entire blank to forming temp then pressed/blown with a mold. Acrylic can be handled the same way, even in you home oven if the piece is small enough, but is much more prone to thinning. A heat gun would be too spotty and internal stress would really much it up unless you were very, very careful.

 

Yesterday I spoke with a polycarbonate representative from GE (the company that manufactures Lexan) and they have all sorts of experts who will help you with this project. In fact, a person included on my conference call was a thermoforming expert.

From my experience thermoforming acrylic by heating it in the oven first and then pulling it over a mold can be frustrating but I have also heard of success with the right amount of patience and practice.

The people I know who HAVE successfully thermoformed plastic over a mold framed up the sheet of plastic in a wooden frame first and then put it in the oven. When they felt it was hot enough they pulled it out and then pulled it over the mold and let it cool. So if I were you, I would shape up a male plug for this surfboard of yours out of foam (something that wont be destroyed by the heat) and then try this out. I have no idea how you'd make good joints between the panels... that you could figure out with some experimentation.
I definately agree with Jehardiman when they say that using a heat gun will be difficult to do well and that the internal stresses resulting from the spot heated areas could lead to disaster while out on those wonderful Cali waves.
So if you're very serious about this give GE a ring and ask for some advice (www.gelexan.com, 413-448-5800)... if you just want to figure things out for yourself, try framing up some plastic sheet in a wooden frame and heating it up at home.

 

I wish you luck in thermoforming Lexan, or any polycarbonate over a compound surface mold. I think you will have the best luck with thicker material, which might be best for your surfboard, since polycarbonate is very very hard to hold at the correct temperature when forming. I have had students spend countless hours trying, with little success, mainly because the thinner films cool too quickly. Our thermoformer doesn't have the heaters directly above the vacuum table, which would probably help, but polycarbonate is still tricky stuff to form. Single bends are as easy as Acrylic. Matched mold pressure forming might be the best way, but is probably cost prohibitive. Any vacuum or air pressure forming we have tried cooled the plastic before it could fit around the molds. As mentioned in a post above, I too would suggest talking to GE Plastics. They are very helpful, especially if your idea takes off and they get to sell you lots of their plastic. Good luck.

ps. All fastening and glueing should be done to GE's specifications. I have seen many Lexan parts destroyed by touching the edge of a cut piece with solvent. It has to do with the way the material is made. One very unhappy boatbuilder I know had to replace all of his installed windows because he cleaned up a bit of caulking around the windows with some acetone.

RWL