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 Post subject: flexy plastic tips
PostPosted: Tue Mar 26, 2013 11:34 pm 
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Joined: Mon Dec 19, 2011 2:10 am
Posts: 174
hello everyone, I am a kiteboardaholic, bought a crap ton of boards, almost found the perfect one in the hadlow freestyle, but not quite there yet, want more bottom end for my weight, so decided to start making them

anyways i havent built a board yet, but decided that i would make fins first using this process...

http://www.swaylocks.com/node/1022521

so i am making my boxes that i am going to make the mold with polytek and i started fiddling with the Lexan i bought at home depot, its 1/4" thick, very bendy

reminds me of the shinn tips, so my question is if you add fiberglass to lexan will it hold it to kiteboarding? if not what type of plastic do shinn boards have for their tips, obviously they have wood in their cores, and my first kiteboard will be a plywood board, but has anyone made tips out of some type of ABS plastic or polycarbonate, if so how?

i also see in my lunacy through the top sheet in the sun, the wood core ends right before the tips and it becomes some type of black core, i am assuming its plastic

now it is my experience that wood tips are better for going upwind cause they are stiffer, but plastic tips are better in the white water and chop, it would be awesome to make a board that has the characteristics of the monk...


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 Post subject: Re: flexy plastic tips
PostPosted: Wed Mar 27, 2013 3:59 am 
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Joined: Thu Jun 05, 2003 3:37 am
Posts: 2362
It's the thickness at the tips that makes for flex, combined with the glass job.
Not so much the plastic.
But the plastic is ABS fyi.
You will do just as well with poured epoxy rails imho.
Just keep them thin enough that they don't force too much springback.
Doesn't really matter.
Some use urethane rails and tips instead, doesn't chip when banged on sliders.
But to the DIYer it's just another learning curve.

Generic recipe:
tips 2.5-3mm thick
center 9-15mm
tips (measured at fin holes) 3-4" narrower than widepoint
rocker
20-25mm = door
25-50mm = normal to wake
>50mm = probably too much
Glass 12-20 oz for strong wood cores poplar cedar spruce etc
Glass 18-40 oz for weak/light core foam balsa paulownia etc
30-50% more glass on top than on bottom.
Outline length and width - benchmark/modify from something you have ridden.
Like maybe copy your hadlow except 1-1.5cm wider...
Hint: do lots of searches and mind the springback
Final hint:
Good boards have a certain amount of 3 dimensional curvature in use.
Square boards ride better with more flex and/or rocker, stiff boards are more fun with some outline curve and rocker... a flatter board may carve fine if it flexes right, etc.


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 Post subject: Re: flexy plastic tips
PostPosted: Wed Mar 27, 2013 8:50 am 
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Joined: Mon Dec 19, 2011 2:10 am
Posts: 174
awesome, thanks for the wealth of knowledge, especially the part about more glass on top, you saved me a bunch of trial and error time :thumb:

gonna keep it simple for my first board and copy a shinn waterbird, this might be interesting to some, not only does the waterbird have a slight amount of rocker on the tips (11 mm from the center), but it has a convex bottom, width wise, not as much as length wise (5 mm form the center) so it sorta has a flat raised bubble like a wainman joke

i guess its what attributes to the boards fun factor

thanks for the ABS answer and confirming the poured epoxy will mimic it...


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 Post subject: Re: flexy plastic tips
PostPosted: Wed Mar 27, 2013 4:44 pm 
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Joined: Sun Sep 04, 2011 5:37 pm
Posts: 1732
If Ya get a bit Too much flex , you can always add = amounts
of 50K carbon-uni on the top & bottom of the board afterward.
Place a few rows of it evenly.
It and can be applied quite Flat ; like the thickness of your gel-coat
flat if Ya spread it out wider.

50K carbon-uni is about $22-25 a Lb when purchased on a roll , which
makes carbon a Bunch cheaper when NOT woven. It "is" more
difficult to work with this way though !
http://www.cstsales.com/carbon_tow.html

The more you add ; the stiffer the board gets, at a minimal addition
to the weight.

That can work the other way around as well ; too stiff, sand some off !

Bille


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 Post subject: Re: flexy plastic tips
PostPosted: Thu Mar 28, 2013 6:52 pm 
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Joined: Mon Dec 19, 2011 2:10 am
Posts: 174
cool, thanks for the carbon info, very resourceful, allthough i don't think i will be messing with carbon for a while


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