Re: Plywood and cork
Posted: Mon Sep 24, 2018 3:56 pm
As I said my board with a cork board core (not just skin got heavy).
I circled back to what should have been my first step .. what are the relative densities of materials?:
Cork
200 kg/m3 for NL-20
http://www.corecomposites.com/products/ ... ecork.html
Paulownia
280 kg/m3
https://www.wood-database.com/paulownia/
EPS Foam
https://markofoamblanks.com/pages/densitychart
2 lb/yd = 0.99 kg/m (I hope I used the correct conversion)
My 50" x 20" x 3/4" cork board ended up weighing 10lbs 7oz compared to my 48X18x1 1/4 paulownia board that came in at 7lb 6oz. Not exactly an apples to apples comparison but I think the point is the same. I might do the actual comparison math later but it seems heavy. Cork starts out lighter than Paulownia but absorbs a lot more resin. As executed, there was no compelling buoyancy benefit to the cork compared to wood.. That was part of my motivation.
A lot of the core cork builds I see in retrospect use templates more like foam body boards but thinner than my build.
In principal I can get some weight out by fairing the cork to seal it against unwanted infusion of resign but that might also make the bond weaker. I could also use unidirectional flax instead of woven flax fabric. The woven flax even with a vacuum took on a lot of resin. The unidirectional that I will use in future projects lays flat and absorbs less to get the same results. I can lay perpendicular layers if I need strength in both directions.
I was able to mold the cork core to get a bit more rocker than I have in my solid wood boards and I also got the right amount of flex compared to my more ridged wood board. With wood you either need to waste a lot of material or do so some splicing to get my target rocker.
I circled back to what should have been my first step .. what are the relative densities of materials?:
Cork
200 kg/m3 for NL-20
http://www.corecomposites.com/products/ ... ecork.html
Paulownia
280 kg/m3
https://www.wood-database.com/paulownia/
EPS Foam
https://markofoamblanks.com/pages/densitychart
2 lb/yd = 0.99 kg/m (I hope I used the correct conversion)
My 50" x 20" x 3/4" cork board ended up weighing 10lbs 7oz compared to my 48X18x1 1/4 paulownia board that came in at 7lb 6oz. Not exactly an apples to apples comparison but I think the point is the same. I might do the actual comparison math later but it seems heavy. Cork starts out lighter than Paulownia but absorbs a lot more resin. As executed, there was no compelling buoyancy benefit to the cork compared to wood.. That was part of my motivation.
A lot of the core cork builds I see in retrospect use templates more like foam body boards but thinner than my build.
In principal I can get some weight out by fairing the cork to seal it against unwanted infusion of resign but that might also make the bond weaker. I could also use unidirectional flax instead of woven flax fabric. The woven flax even with a vacuum took on a lot of resin. The unidirectional that I will use in future projects lays flat and absorbs less to get the same results. I can lay perpendicular layers if I need strength in both directions.
I was able to mold the cork core to get a bit more rocker than I have in my solid wood boards and I also got the right amount of flex compared to my more ridged wood board. With wood you either need to waste a lot of material or do so some splicing to get my target rocker.