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 Post subject: Rocker for Plywood Board
PostPosted: Sat Jul 03, 2010 2:39 pm 
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I've read about various methods to put a bit of rocker into a plywood board.
-steam with iron
-soak in pool
-laminate two sheets on rocker table

Now I wonder what method is most promising for my application.

Here is what I have and want to use:
I am planning to use a 1/2" sheet, so the laminating method falls away. I do NOT want to use any glass, just spar urethane as finish.

Here is what I am worried about:
I heard that soaking the ply in water or steam it would weaken the glue. I assume that would mean it could de-laminate, or split open the layers prematurely.

Is this concern valid or just a myth?

Also, I would like to learn how long one has to dry the wood out after soaking or steaming. What method have you used and would recommend?

Thank you all.


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 Post subject: Re: Rocker for Plywood Board
PostPosted: Thu Jul 15, 2010 3:40 pm 
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Hey, nobody any input? I am done with my second plywood shape and I am trying to put some rocker into it.

Lack of feedback, I am trying it with steam iron. Only did it a few minutes on each end section of the board and put some heavy sand bags on it supporting only the end tips.

I will keep posting progress. It seems to have put some rocker into it but I wonder if it holds once the bags are removed for some time?!


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 Post subject: Re: Rocker for Plywood Board
PostPosted: Thu Jul 15, 2010 7:42 pm 
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Joined: Sun Dec 15, 2002 1:00 am
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Location: Argentina
i'd go for the laminate. i've made a few boards with this methods and the results were ok.
about the resin, go for epoxi, poliester is not a good glue and will delaminate after some time
pablo


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 Post subject: Re: Rocker for Plywood Board
PostPosted: Thu Jul 15, 2010 8:06 pm 
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Gluing wood into a curve holds it to the curve.
Plywood's already glued together straight,
so you are always fighting against that to put rocker in.
Making a laminated rockered board, you overcome this.
You can also hold some rocker in it by putting fiberglass on the deck though, if you don't want to do multilayers of plywood for rocker.
Epoxy works well.
2 layers of 1/4 ply glued together with a waterproof PL adhesive could also work well though, and cost 80% less.
You could use polyurethane glue ("gorilla" etc) too, but it would require a lot of clamping to ensure a good bond.


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 Post subject: Re: Rocker for Plywood Board
PostPosted: Fri Jul 16, 2010 7:46 am 
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Location: Iv.G.-Slovenia
@daspi
did you wonder why nobody use's this 'simple' methods?
zero prestige (home page) has some ply board methods
the only way I see, how you can get some rocker on a board from one pc of ply board (without adding any inner tensions) is by sanding it down. Maybe glue a pc at the tips to get some material for some extra rocker. But that's no longer from one pc :D


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 Post subject: Re: Rocker for Plywood Board
PostPosted: Fri Jul 16, 2010 1:16 pm 
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I have had some success with kerfing the wood. You use a table saw and cut some thin slots across the board in areas where you want rocker.

Then you can apply some hot water and easily bend to create the rocker you want.

Once you have the rocker, you need to fill the kerfed slots with epoxy. I do this by putting duct tape at the end of the slot so the epoxy does not run out - then fill it with epoxy. This is strong and will lock in your rocker.

BTW, don't build too much rocker in. 1/2"is good for light wind board and 3/4" for high wind chop and waves. Also, most plywood is now laminated with waterproof glues.

E


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 Post subject: Re: Rocker for Plywood Board
PostPosted: Fri Jul 16, 2010 2:14 pm 
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ed257 wrote:
I have had some success with kerfing the wood. Once you have the rocker, you need to fill the kerfed slots with epoxy.


We used similar method in furniture production for round doors, panels and similar products.
Except this were still glued together from 2 pieces. Both kerfed on one side. No water was used to bend it, and the slots were not filled with resin. We only applyed it on the surface of both plates so the cured plates hold one another. By this method you get lighter product, than filling the slots.
We used a 2K PU resin, about 3 or 4 times ticker than epoxy. I use it too, for my cores. I found it much better for this job, than epoxy.
Anyway, I would use 2 ply's for this method with kerfing.

BR,
Zob


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 Post subject: Re: Rocker for Plywood Board
PostPosted: Wed Jul 28, 2010 11:06 pm 
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Poster Pablo is correct about lamination it is the best way to get rocker however u have to use one quarter inch plywood on top of another one quarter inch peice if u want one half thickness he is also rite about epoxy being a better glue u can get away without fiberglass but it is not as strong I have build many like this prop up each end one and one half inch and make the center flat it will work I rode one just like that in San Quintin Mex. last weekend


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 Post subject: Re: Rocker for Plywood Board
PostPosted: Wed Dec 22, 2010 6:30 am 
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zob wrote:
We used similar method in furniture production for round doors, panels and similar products.
Except this were still glued together from 2 pieces. Both kerfed on one side. No water was used to bend it, and the slots were not filled with resin. We only applyed it on the surface of both plates so the cured plates hold one another. By this method you get lighter product, than filling the slots.
We used a 2K PU resin, about 3 or 4 times ticker than epoxy. I use it too, for my cores. I found it much better for this job, than epoxy.
Anyway, I would use 2 ply's for this method with kerfing.



It would help me a lot if I could learn how this kerfing works. I would probably need this for my wood designs. But I am not good as others yet, I am new in the business.

Info: Memphis Patio Furniture


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 Post subject: Re: Rocker for Plywood Board
PostPosted: Fri Jan 14, 2011 5:50 pm 
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Dude,

It easy as. did one two weeks ago in two hours, with both concave and rocker

Laminate using any two pack expoxy 2 6mm pieces of marine ply (make the top piece a bit shorter, maybe some cut out to improve flex i the tips.

on a stiff table place a piece of wood in the middle of the board between where your feet would be (concave). and blocks under the tips (rocker).

Mix and wet the uderside of the upper piece and wet the lower

clamp down the sides (single point per side for constant rock - chop hing wind) or two point for a flat section in the middle (lower wind)

I did this with 120 x 48 ply with fine results (board is a bit short but worked fine up to 25 knots). 120 is what th stor had precut (i'm lazy).

Cost wood + resin ----$50. I didn't even paint it. i will get round to it a some point.

Hope this helps.

Mike


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