Forming the rocker in paulow

[BWD]

My experience: the "standard" for springback from a 3-6cm rocker with a 12mm softwood core is indeed about 50-60% with 18-20oz fiberglass on each side, assuming a good cure is reached before the board comes off the table. With typical surfboard or boat type epoxies this means 24h minimum. Even if the hardener is "fast"
If you can't or don't want to run vacuum this long, remember vacuum does 2 things (1) laminate consolidation/resin control and (2) puling the core down to the table/mold. Once the gel time of the resin has passed, the vacuum is not really needed for (1). Clamps or weights can be used to hold the board on for the rest of the cure. Silently.

How to get it right: the test strip.
Start with a rectangular core "blank" several cm wider than your board dimensions. Outline the board on it, offset to one side a bit, so you have say 8-10cm extra on one side, less on the other. Cut a strip minimum 5cm wide off the side with "extra." This is your test strip. Taper it like your board will be tapered. Lay it up with the same glass schedule and laminate it on the rocker table, top side only. After full cure, take it off and measure springback. Did you get your rocker? If not, you can gain a little more (3-6mm probably) by laminating the bottom of the board with the board (bottom up) in a jig that bends it a little more by clamping the tips to a flat surface and supporting the middle of the board with wood blocks or whatever to give it more curve. Try it with the test strip! All of this manipulation of the board can be made easier if you do not free the board from its blank until after lamination, btw. Clamps and scews etc can be used through the part of the blank outside the rails. Also, if you use poured urethane or other flexible plastic to form the rails, they will not interfere with bending the board onto the table/jigs. Epoxy rails can cause extra springback.

If your rocker is really off, and you're not satisfied, adjust taper, rocker table, laminate schedule as needed and repeat with another test strip. Once you are getting your rocker, laminate the actual board.
Naturally, this methodology is more suited to those who build their own blanks (or can buy extra wide blanks to make skinny boards). It works for me, but there is more than one way to skin a cat.

@rynhardt:
While conventional TT build strategy wants a continuous core as the properties of both the core and the laminate contribute to strength, flex, and damage tolerance, kerfing the core can have a place, as can tapering it, especially if the kerfs are filled or partly filled, or bridged by a composite skin -veneer, foam, whatever. Some boards I have made have used strips with a trapezoidal section instead of rectangular, so the glue holding them together at the blank stage is only in the bottom ~1/3 (though probably top 1/3 would work better). This helps the side to side flexibility of the core on the mold to make concaves, and avoids creating many "micro-stringers" in the glue lines of the core in its flat stage.
Kerfing side to side or diagonally can have a role in achieving tail or nose kick in solid-core wood composite directionals, while with hollow wood composite directionals, the skeleton inside the skins can be designed other than a stereotypical "fishbone" to suit the project's needs. With your creative approach , you can probably come up with some good strategies...

[wood1]

Hello all ,
I have been pre bending my paulownia cores to an exaggerated rocker and concave
after wetting the core with water ,letting it sit for a week and than letting it relax on the "true" rocker table
it works beautifully, I will start a new topic with pictures to explain,

good winds

Itai.

[BWD]

that is one of the nice things about that paulownia, good tip. It also steams well I hear. I usually use cedar, which doesn't. Some day I may switch, but cedar is available and inexpensive for me.

[downunder]

I think there is no need for wetting the wood. I mean, after the wetting how long it takes to dry? How would one judge this in a DIY environment?

So, back to the rocker. The problem is 12mm wood core and a huge 6.5 cm expectation (this sounds
weird
Even if you test on the wood strip, ie 5cm wide as BWD suggested, you've got a whole plank with different wood properties at places. And, it is incredibly strong (got one in a shed 1500x48x12).

Triax FG only is not suitable for this. You’ll get >90% springback with triax, and no concave with it at all (you did not mention a concave?).

Not sure how the wakeboards are built, I think they are much thicker? Which might mean they are a double layer wood cores and this is how I would build it (but not a kiteboard).

[MFR]

Thanks guys.

I am taking all your comments into consideration.

I like the idea of pre bending the board before lay up this should help reduce the spring back which I really do not want.

I think I may look into wetting the wood or possibly building a steam box for the board. I will clamp it up for a week or 2 and see how the shape holds before I lay it up. I have a tool to measure the moisture in wood so this will not be a risk.

I will create a new post for my build so far and update as I complete it.

I wanted to try and build the board as quick as possible. But being my first bard and joining this forum I have now decided to take my time.

YOU CANT RUSH PERFECTION

[rynhardt]

yeah man, don't rush it. You've put in a huge amount of time already and want to have something to show for it. I'm guessing at least 40 hrs?

experiment on scraps first until you get consistent results.

[MFR]

Time wise it has taken me about 12 hours labour time building the rocker table, tip jig, board template and the board its self up to pre bending stage.

Obviously there is waiting time for the resin to cure in the rails. Do you count this time aswell?

I am so excited to get it complete and down to my cable park but i need to be patient and focus