Stress in Blanks?

I have never cut the stringer out of a blank to see if the blank would return to its unrockered shape (post production, or that shape it had when it came out of the mold.) I assume it would. Has anyone done this, or had some experience that would suggest that this assume is correct? How much of the rocker remains, if any? Does the age of the blank matter, i.e. the older the blank the more rocker will remain if the stringer is removed, or in more technical terms, will the already (mostly) cured foam relax under the applied stress.? Please blame this new interest on the Jim Phillips Master Shaper video. Apparently Jim points out the humps at the rocker transition points, which can be quite significant, at least apparent in a 10 foot blank. As a result, I’m now dead curious as to whether or not these humps are under tension, and what that level of tension might be. Are they prestressed? I would presume they are. Maybe somebody has a good technical contact at Clark Foam they wouldn’t mind sharing? Kevin

I recently took out the stringer of a 10 footer, that had snapped more or less in half. I wanted to glue up a new stringer and create a 6’4" fish. Anyway after removing the wood from foam, the rocker remained constant. My thoughts are that the foam is not uner any stress due to the fact the in the manufacturing process they blow the foam into the preshaped mold. So there is no tension on the blank once it pops out of the mold. And cutting the blank in half to slap a pice of wood in the middle should not apply any tension to the blank whatsoever.

I recently took out the stringer of a 10 footer, that had snapped more or > less in half. I wanted to glue up a new stringer and create a 6’4" > fish. Anyway after removing the wood from foam, the rocker remained > constant. My thoughts are that the foam is not uner any stress due to the > fact the in the manufacturing process they blow the foam into the > preshaped mold. So there is no tension on the blank once it pops out of > the mold. And cutting the blank in half to slap a pice of wood in the > middle should not apply any tension to the blank whatsoever. My experience as well. Ditto.

I would think that if you have rocker adjustments other than natural, you would have stress. Don’t they bend the foam and clamp to match the stinger in glue up? guess it would depend on how green the blank is when it is glued.

My experience as well. Ditto. So the suggestion is then that the rocker in say a standard blank as ordered is not put in the blank post production, but is the same rocker out of the mold, and that the foam in not prestressed!? (Excluding custom rockers adjustments.) Really? So maybe I’m seeing humps that aren’t there… maybe I need glasses? Or maybe there are humps but its just the way they designed the blank mold? Or maybe its just the transition point, it just seems meatier? Straighten me out Dale (no pun.) Do I need glasses? Kevin

I recently took out the stringer of a 10 footer, that had snapped more or > less in half. I wanted to glue up a new stringer and create a 6’4" > fish. Anyway after removing the wood from foam, the rocker remained > constant. My thoughts are that the foam is not uner any stress due to the > fact the in the manufacturing process they blow the foam into the > preshaped mold. So there is no tension on the blank once it pops out of > the mold. And cutting the blank in half to slap a pice of wood in the > middle should not apply any tension to the blank whatsoever. Hey Drew please see my response to Dale’s Re: Stress in Blanks? (Dale Solomonson) The final question being, am I seeing things that aren’t there? Kevin

I have never cut the stringer out of a blank to see if the blank would > return to its unrockered shape (post production, or that shape it had when > it came out of the mold.) I assume it would.>>> Has anyone done this, or had some experience that would suggest that this > assume is correct? How much of the rocker remains, if any? Does the age of > the blank matter, i.e. the older the blank the more rocker will remain if > the stringer is removed, or in more technical terms, will the already > (mostly) cured foam relax under the applied stress.?>>> Please blame this new interest on the Jim Phillips Master Shaper video. > Apparently Jim points out the humps at the rocker transition points, which > can be quite significant, at least apparent in a 10 foot blank. As a > result, I’m now dead curious as to whether or not these humps are under > tension, and what that level of tension might be. Are they prestressed? I > would presume they are.>>> Maybe somebody has a good technical contact at Clark Foam they wouldn’t > mind sharing?>>> Kevin Kevin, each blank has what is refered to as natural rocker, this is what the deigners created and variations from this cause the blank to be tweaked. The blanks are very flexible, but during the gluing they can be torqued out of alignment. I often saw the center sticks out for KKL when the gluing instructions have gone astray. As the blank is released from the stick, it does try to return to its natural state. The bumps themselves aren’t under any kind of real tension. But eveidence of this can be seen in machine shaped blanks that are glued to rockers other than natural, it is what they refer to as relaxation. As the machine cuts away the foam, the blank is trying to return to its natural state, this results in the blank having slight differences from side to side as more and moe foam is removed.

Kevin, each blank has what is refered to as natural rocker, this is what > the deigners created and variations from this cause the blank to be > tweaked. The blanks are very flexible, but during the gluing they can be > torqued out of alignment. I often saw the center sticks out for KKL when > the gluing instructions have gone astray. As the blank is released from > the stick, it does try to return to its natural state. The bumps > themselves aren’t under any kind of real tension. But eveidence of this > can be seen in machine shaped blanks that are glued to rockers other than > natural, it is what they refer to as relaxation. As the machine cuts away > the foam, the blank is trying to return to its natural state, this results > in the blank having slight differences from side to side as more and moe > foam is removed. So, if I ordered a 106S without a stringer, it would show up with its natural rocker as listed in the catalog? I could then put in my own stringer, not really having to worry about any else but alignment? (That is, I wouldn’t have to bend the blank to get the (listed) natural rocker.) Kevin

YUP. Not an expert but I believe so. So what kind of stringer were you thinking about gluing in???

YUP. Not an expert but I believe so. So what kind of stringer were you > thinking about gluing in??? Balsa. 2 inches of it. Stiff and beautiful. Kevin