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Rocker mold help

Posted: Mon Nov 21, 2011 4:28 pm
by COsurfer
I am making a full rocker mold and trying to figure out how much rocker in my mold to get a final tip/tail rise of 8mm-ish. I tried a 10mm rocker mold and the board went flat out of the press. I tried to search the forum but that is pretty much useless. Any help would be greatly appreciated.

Posted: Mon Nov 21, 2011 4:57 pm
by Huck Pitueee
the first board I molded came out nearly flat. So I went to a 3 layer core. Lots of work but comes out of the mold spot on.
base layer with inserts.
Image
mojomo005 by Huck Pitueee, on Flickr

Middle layer with tapers

Image
mojomo006 by Huck Pitueee, on Flickr

top layer

Image
mojomo007 by Huck Pitueee, on Flickr

Posted: Mon Nov 21, 2011 5:12 pm
by Huck Pitueee
I keep thinking the top layer of glass should be the pre stressed and cured sheet you can buy. I haven't tried it yet. When you mold a full rockered board the top layer of glass is being compressed as it gets molded.

Posted: Fri Nov 25, 2011 10:22 am
by 24Dave
HP, I don't get it. Wouldn't you only be compressing your top layer of glass if you glassed the top layer and cured the core flat, then pressed the core into the mold and laminated the bottom layer. A rockered ski/board made from a flat core would, at rest, would be held in a rocker curve from tension on the top layer and compression on the bottom layer. Same for your wood layers, except you can create a lot stronger curve in the core the way you put them together than just relying on the composite to hold the rocker and tip and tail curve. Wouldn't you laminated core hold the shape, and your glass layers wouldn't be in tension or compression?
-Scooby2

Posted: Fri Nov 25, 2011 10:49 am
by rockaukum
I have done several skis and a couple boards with rocker. I do not use a heated press. I do heat the room to about 100* or so depending on the weather. You may find luck by leaving the board in the press for a full cure. Check epoxie recomendations for times. I have not measured the amount of relaxing the skis do as I just don't care too much. But it seems to be about half. If I shim the press to 8mm i would get about 4mm finished rise, kinda the same for camber. Check old pressings and measure the camber of the finished product vs the mold used. Good luck
ra

Posted: Sat Nov 26, 2011 3:44 pm
by Huck Pitueee
24Dave wrote:HP, I don't get it. Wouldn't you only be compressing your top layer of glass if you glassed the top layer and cured the core flat, then pressed the core into the mold and laminated the bottom layer. A rockered ski/board made from a flat core would, at rest, would be held in a rocker curve from tension on the top layer and compression on the bottom layer. Same for your wood layers, except you can create a lot stronger curve in the core the way you put them together than just relying on the composite to hold the rocker and tip and tail curve. Wouldn't you laminated core hold the shape, and your glass layers wouldn't be in tension or compression?
-Scooby2
Proof that the top layer of glass gets compressed is I always see waves especially on the tip & tail where the glass is bunching. Yes the core without glass would hold the shape of the mold some but there would be some spring back. The reason the 3 layer core holds its shape is because the layers slip against each other. Just the act of pressing the top layer into a rockered mold is trying to shorten the fibers. Just think that each layer of materials farther from the mold has a tighter radius and if it doesn't slip against the other layers like a pre cured sheet would the fibers would be forced to shorten.