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Veneer topsheets, wood sidewalls and increasing rocker

Posted: Fri Jan 25, 2013 1:49 pm
by falls
Hi everyone just thought I would run past you guys a theory/problem I am having.
Most of my skis seem to be getting more rockered with time. It isn't happening on the ones I pressed room temp with west but is on the heat cured ones with sicomin epoxy.
I have heated them all from the top only so appreciate the loss of camber/gain in rocker from this. However it seems the rocker is increasing more with time.
It seems most pronounced on the skis with veneer topsheets.
It is hot where I live (regularly over 40C/104F or more) and I have noticed that over summer the bolts on my press forms (MDF) have loosened as the wood has dried and shrunk.
I wondered if the same was happening on my veneer tops. The veneer dries in the hot weather and contracts. Contraction on the top surface tends to rocker the ski or reduce its camber. It seems most pronounced in tip and tail perhaps where core thickness is less so less strong at overcoming the pulling force of the topsheet. (I also wondered if a drying core with exposed sidewalls could compound this phenomenon).
Any support for this? Or other ideas.
I will take the skis into the cold next week (-15C/5F) and higher humidity and see what they look like.

Posted: Fri Jan 25, 2013 5:27 pm
by Head Monkey
That’s interesting... I have not noticed that with my veneer boards, but it’s fairly even humidity where I live year round. I have read and been told many times that in traditional woodworking, when you apply veneer to a panel (like, say, 1/2" or 1/4" plywood) that you should always apply veneer to both sides, otherwise the panel will bow and cup over time with moisture changes in the veneer. Perhaps as you speculate you are being affected by this given how hot and dry your summer appears to be. I’ll be interested to hear what happens when you get them into a higher humidity environment.

Posted: Fri Jan 25, 2013 6:18 pm
by Dr. Delam
All of my skis definitely change according to temperature. In the summer months when it is warm they all lose camber. It seems that different top sheets have different coefficients of thermal expansion. So you might see inconsistent changes depending on what you are using. I haven't used veneer but I wouldn't worry about it. I think they will return back to normal once they are in the regular skiing environment.

Posted: Fri Jan 25, 2013 7:37 pm
by skidesmond
That's very interesting. I haven't noticed that kind of movement in my skis where I live, but I know from wood working experience wood in general will move a lot depending on the specie of wood with temp and humidity. Also the way it is cut can effect the movement. For example a flat or plain cut will have more movement than say a 1/4 sawn cut.

Kilned dried wood is usually pretty stable but different species move more than others.

Posted: Fri Jan 25, 2013 11:17 pm
by OAC
Dr. Delam wrote:All of my skis definitely change according to temperature. In the summer months when it is warm they all lose camber. It seems that different top sheets have different coefficients of thermal expansion. So you might see inconsistent changes depending on what you are using. I haven't used veneer but I wouldn't worry about it. I think they will return back to normal once they are in the regular skiing environment.
Bulls eye!

Posted: Sun Jan 27, 2013 6:40 am
by falls
Thanks.
In transit in Singapore. Will report when I am back on snow in a day or so.
50cm last night where I'm going :)

Posted: Tue Jan 29, 2013 1:46 pm
by falls
doesn't seem to have changed the rocker/camber profile getting into the cold weather.
on the upside there is fresh snow and the added rocker will not be disappointing :)