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Plywood Replica of WT147 - need rocker specs

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Plywood Replica of WT147 - need rocker specs

Postby Guest » Sun Mar 30, 2003 4:40 pm

I am in the process of making a plywod replica of WT147. I got the outline by downloading a top-view picture of the real board, printed it on a transparency. Then I used an overhead projector and adjusted the distance until the lenght and width dimensions exactly matched board specs. Then I traced it on to the plywood and cut it out.

Now I am ready to put in the rocker and flip tips. I was hoping someone who has a WT147 could help me by providing rocker specs. Either that, or a digital picture directly side view showing the rocker. With a side-view picture I could use the projector again to scale it up to full size.

I will use the kerfing technique (partially cutting through the plywood) in order to flip up the tips and will be using west systems epoxy and cloth on the plywood for strength and waterproofing.

Eduardo :)

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Postby not annonymous » Sun Mar 30, 2003 4:48 pm

Sorry, haven't seen the wave tray, but you should know that your plywood board won't handle that same way as the the foam board.

plywood is way more flexible, so you'd be better off using a rocker that is flatter than the board you want to copy if you want similar riding characteristics.

Guest

Postby Guest » Sun Mar 30, 2003 5:28 pm

Good point, but because I am using cloth and epoxy on top of the plywood, the board will be stiffer than typical plywood and will more closely approximate the stiffness of the original.

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Postby sq225917 » Sun Mar 30, 2003 5:48 pm

well if you are going to laminate a wood deck make sure you give the deck a thin coat of just resin first. cos if you just glass straight onto it, its going to peel off real quick, as there is such a difference betwen the flex characteristics of the two materials. the glass will just buckle on the top side of the board as its not able to deal with the compression stress. unless you put a shit load on that it.

more than 3 layers being a shitload....

foam and glass go together well because of their surface adhesion properties and similar flex giving managable shear components in the board.

best of luck.

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Postby Guest » Sun Mar 30, 2003 7:19 pm

sq225917 wrote:make sure you give the deck a thin coat of just resin first. cos if you just glass straight onto it, its going to peel off real quick, as there is such a difference betwen the flex characteristics of the two materials. the glass will just buckle on the top side of the board as its not able to deal with the compression stress. unless you put a shit load on that it.

more than 3 layers being a shitload....

.
Are you recommending that I coat the wood with epoxy and cure it first and then apply the cloth and a second coat of epoxy, or are you saying to apply epoxy to the wood and put the cloth down quickly before it is cured and wet the cloth with epoxy from the top side?

Do you think it would be better to put the glass cloth on the bottom side instead of the top?

It seems to me that foam and cloth also have entirely different characteristics.

Eduardo

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Postby Guest » Mon Mar 31, 2003 3:28 am

The rocker on WT147 is pretty flat except for the flipped up tips.

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Postby KiteGlider » Mon Mar 31, 2003 4:41 am

Yes, Eduardo.
I have the same question to SQ, apply a coat and cure or laminate and glass in one step.
Another thought comes to mind to prepare the plywood surface for the glass laminate adhesion. For example roughing up the plywood surface with a wire brush power drill attachment.

Maybe a crazy idea, but I want to try using carbon tube rod stringers to maintain rocker and add strength to the ply glass laminate.

Just one source
http://www.intothewind.com/cart/supplies.html

When I was looking for Cquad replacement rods I realized there are several good sources of carbon rods normally used to build sport kites.
Funny that they could be used as re-enforcement structure for a "kite-board".

KG
p.s. To Eduardo, if you register, then others can send notices by PM mail
AND you can edit your posts if you need to.
Last edited by KiteGlider on Mon Mar 31, 2003 5:00 am, edited 3 times in total.

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Postby not annonymous » Mon Mar 31, 2003 4:43 am

Anonymous wrote:
Do you think it would be better to put the glass cloth on the bottom side instead of the top?

It seems to me that foam and cloth also have entirely different characteristics.

Eduardo
On my plywood boards I put 6oz/yd glass on top and bottom. I use 3 layers 3mm birch plywood for the core. It is still pretty flexible like this and it is possible to break them, though not very easy.

For a solid wood core for sure it is better to put the glass on the bottom if you only do one side, because these composite fabrics are all strongest in tension and weaker in compression. When you flex the board the top is in compession and the bottom is in tension.

The boards that I have broken failed in the bottom glass and bottom layer of plywood while the deck glass and plys remained intact and seemed to show no signs of excessive stress.

I would not coat the wood with epoxy and allow it to cure before applying the glass. If you do this you need to wash off any amine blush if you are using an amine hardner like West System and many other brands. You also will want to sand it smooth which can be a PITA with straight resin.

It is a good idea to coat the wood with epoxy 10-20 min. before laying on the cloth, then using more epoxy to wet out the cloth. This way when the wood soaks up a little bit of the epoxy you won't end up with any dry spots in the laminate.

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Postby zfennell » Mon Mar 31, 2003 6:00 am

Eduardo[/quote]

For a solid wood core for sure it is better to put the glass on the bottom if you only do one side, because these composite fabrics are all strongest in tension and weaker in compression. When you flex the board the top is in compession and the bottom is in tension.

.[/quote]
:o
I may be a little offbase here:
But the phrase " A chain is only as strong as its weakest link" seems appropriate.
Adding glass to the "strong link" doesn't make the weak link go away.
If your board is inclined to fail in compression, you have done nothing to reduce those stresses.
IMHO -bill

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Postby R a i n e r » Mon Mar 31, 2003 6:13 am

I've made myself 4 woodies so far without any glass or carbon.
That's much lighter (2,5kg) and it's just superfluous!
You better adjust the stiffness by using more layers (4-5) in the middle of the board and less layers (3) at the tips!

:thumb:
Wood rules!

Rainer


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