Losing camber

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MLReed05
Posts: 82
Joined: Sat Jun 10, 2006 5:12 pm
Location: Western MA

Losing camber

Post by MLReed05 »

Cant figure out why I am losing camber....heating for 175F (1hr) then letting the mold cool to room temp. Any thoughts on this????

The main difference in what I am doing from others people's method is that I heat from the top... anyone else do this?

justin56
Posts: 24
Joined: Wed Oct 11, 2006 6:04 pm

Post by justin56 »

Hi MLReed05,

My experience is that using only one heat source you get better camber results when heating against the base side.

In reality, you should be able to do what you are doing with heating from the top, but only when all variables in materials (how they react to heat and pressure) have been taken into consideration. You may find you need higher tempuratures.

From personal experience it is far easier to simply heat from the bottom (base side) than to try to deduce with any empirical certainty what something like a base plastic will do under all heat and pressure conditions. The manufacturers of said materials certainly dont' track that and they have the battery of equipment and scientists to measure just that!

One thing to keep in mind is that some builders put camber in after pressing and once the ski is out of the press in a "camber rack." I've had mixed results using that method. Some even place the ski and camber rack in an oven to bake the camber into it!

I suppose if I thought I wanted a pair of skis to last only one season I'd do that--did anyone mention inbuilt obsolesence? But, I'm old school and like anything I build to stand the test of time.

MLReed05
Posts: 82
Joined: Sat Jun 10, 2006 5:12 pm
Location: Western MA

Post by MLReed05 »

I pressed again with my heat blanket on the bottom. This time my ski came out with more camber than the mold has.

Bambi
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Joined: Sun Jun 04, 2006 6:01 pm
Location: Boston

Post by Bambi »

On average you are doing pretty well then.

B ;)

G-man
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Location: northern sierra nevada

Post by G-man »

bambi wrote:
On average you are doing pretty well then.
G-man chuckles. :)

BigG
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Joined: Mon Jan 02, 2006 2:41 pm

Post by BigG »

Now with two blankets ;-) (not both on top or bottom :-))

G-man
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Joined: Sat Mar 25, 2006 3:58 pm
Location: northern sierra nevada

Post by G-man »

Okay, time to get serious. MLReed05's findings kinda fit a theory I had a few months ago... goes like this:

When pressing in a heated press with the heater on the bottom, the bottom few millimeters of the ski heat up much more quickly than the top surface of the ski, simply because the upper mass of ths ski is further away from the heat source. When the lower glass layer reaches 150 degrees, it hardens like a rock, while the upper layer of glass is still in the process of heating and expanding. Whereas the bottom layer of glass heated up and expanded in a relatively short period of time, the top layer of glass has much longer to expand before it's epoxy sets, giving the top layer of glass a longer relative length than the bottom layer. When the ski comes out of the mold, tension and compression forces are freed up, and camber increases due to the greater expanded state of the top layer of glass.

Now, MLReed05's first ski lost camber when the heater was on top and the second ski gained camber when the heater was on the bottom. It seems to fit my theory's predictions, but, who knows. Surely, other builders will report exactly the oppposite results. Anyway, the theory is what caused me to decide to heat from both top and bottom. I haven't completed the conversion yet, so I have no results to report.

G-man

MLReed05
Posts: 82
Joined: Sat Jun 10, 2006 5:12 pm
Location: Western MA

Post by MLReed05 »

Gman-
I think you hit the nail on the head with that theory. Looking foward to see what happens with two heaters...keep us posted.

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Head Monkey
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Post by Head Monkey »

I really like these: http://www.omega.com/pptst/5LSC_5SRTC.html I used the 36awg size. I’m heating with two blankets, controlled by one controller. But I have two sensors and two temp displays. I place one directly above the bottom blanket in the middle of the board, and the other directly below the top blanket in the middle of the board. They are so thin that they barely leave an impression in the blanket, and their response time is amazing. I control my heaters with the bottom thermocouple only. The top one lags the bottom one by up to 30F for the first 20-30 min of heating when starting from 70F and going to 170F. Those are temps right against the blankets. The thermocouples come in packs of 5… one day soon I plan to embed two of them directly into a board: one in the top layer and one in the bottom layer to get a true measure of relative heat between the layers when pressing.
Everything I know about snowboard building, almost: MonkeyWiki, a guide to snowboard construction
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