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Wood Board Spring Back

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kriskris
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Wood Board Spring Back

Postby kriskris » Wed Nov 21, 2012 2:24 pm

Hi everybody,
I tried to build wooden board with poplar core. I used my home built pneumatic press.
My board is 132 cm, 8-9 mm in the middle and 2-3 at he tips. It came out with almost no rocker. What is your experience with spring back? How much should I correct the rocker table for poplar or cedar core with fiberglass layup? Thanks. kris

BWD
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Re: Wood Board Spring Back

Postby BWD » Wed Nov 21, 2012 3:00 pm

Rule of thumb for laminating wood is to lose 30-50% of the curve in a lamination of 2 pieces.
For a 9mm cedar board with 18oz (600gsm) e-glass and a medium-modulus surfboard epoxy cured at room temperature, I have found the rocker loss to be about 50%.
It is critical to get a full cure of the epoxy.
Even with fast hardener, with a room-temperature cure I leave the board on the table for several days before removing it!

kriskris
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Re: Wood Board Spring Back

Postby kriskris » Thu Nov 22, 2012 12:58 am

Thanks BWD. Correct me if I am wrong. You are saying that with this type of lay up you have to double the rocker dimension to get expected curvature at the tips?

BWD
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Re: Wood Board Spring Back

Postby BWD » Thu Nov 22, 2012 2:21 am

Yes. Approximately. Last board was 9mm cedar, 3mm tips, 600gsm glass, epoxy. About 5.8cm on table, final result 2.8cm. The tapers only run from the middle of the strap.positions to tips though. Between straps the center is all full thickness. If the tapers ran a little closer, say to the inside inserts, the rocker might hold a bit more easily.....

kriskris
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Re: Wood Board Spring Back

Postby kriskris » Sat Nov 24, 2012 4:30 am

Thank you BWD.

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vol
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Re: Wood Board Spring Back

Postby vol » Fri Dec 28, 2012 11:11 am

Keep rocker helps 2 layers of glass fabric on top and bottom, and BWD is right, If you use room temperature keep board in press 2 days at list


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