:: View topic - Heated Press and camber issues

After the first 2 skis came out with too much camber (Kaffienes and Daddies little girl), I modified the mold to have only about 5-6 mm of camber. We were able to try out the new mold this past week and lo and behold, the camber doesn't change. Our new skis still have way too much camber (>25mm). We are thinking the thermal expansion of the materials, especially the edges, is causing the camber to increase as the edges cool and contract after pressing. One pair has titanal on the bottom and the camber is much greater than the pair without.

Is anyone else having the same problems? One thought is to reduce the temperature. Another idea is to build a negative cambered mold and hope some of camber cancels out. Other thoughts on the issue?

-kelvin

Are you allowing the skis to cool in the press?

I just pulled a board out of my press and had the same issue. Maybe I should try letting it cool in there too?

In my heated blanket press, I haven't experienced this issue at all. I am throwing a ski in there tonight, and I will get a thermometer in there to find out how hot it actually gets.

We rip them out of the press smoking hot.

I'll definetly try letting them cool before taking them out. However, it seems that the epoxy is already at a full cure and everything is set in place at the extended lengths.

-kelvin

I'm no expert on the issue, but I have definatly heard that boards/ski's in heated presses should go through a heat/cool cycle before you take them out. I would guess that you should let them cool under pressure for approximatly the same amount time as you have them heated. I have also heard that the longer they cool under pressure the better the result.

what about using symmetrical metal layup like in the karhu video? maby this will "balance" the thermal expansion?

I heard some factories use diferent temperatures at the top and the bottom. maby to compensate?

Hello!

I cure my skis at room temp and have 10-15 mm camber built in to my moulds, the amount of camber varies with length. Sometimes I speed up the curing process by heating to ~35-40 celsius and I gain more camber, about 5 mm.

I think it is the steel edges that expand and contract different from glass laminates. The steel is the only part that my skis that are assymetrical with respect to the camber. Top sheet and base material are to soft to contribute to thermal relaxation tensions, probably.

My tip is: If you go for a heated press, optimize everything for a certain temp and stay to a certain material configuration. As soon as you differ material and/or temp you do not know what happends to your final product.

Henrik

Henrik

Hi Henrik,

At room temperature cure does your ski come out with the designed in camber or does it relax a bit? I am building 170cm skis and the mold has 15mm camber but I want the final ski to be no more than 10mm.

Thanks Tony

Hi Tony!

Yes they do, they relax 5-10 mm depending on length. I have a soft light core that does not contribute to the flex very much so you may experience differeces from my relaxation. But otherwise it sounds good with 15 mm of camber in your mold! Though I have a little less camber for a 170 cm ski, ~10-12 mm.

Good luck!

Henrik

I am in the beginning stages of designing a ski for myself

While looking at other skis I have I've noticed a few things.

Some skis (park skis mainly) are mounted directly in the center. this is also right at the apex of the sidecut.

Other skis are mounted somewhat behind the centerline of the ski. I'm not able to determine whether the sidecut apexes at this point, or at the very center of the ski. Do you think there'd be any advantage to adjusting the apex of the sidecut arc to correspond to the center of the mount point rather than the center of the ski?

I know there's a book on the physics of skis, but it looks like a pretty involved read... I've only taken first year physics... I've always figured hell was something that *might* happen at the end of one's life. Not a self inflicted learning experience selected in one's prime.

I think it depends on the type of riding you'll be doing. From what I've noticed, most skis have the sidecut centered a bit ahead of the center of the mounting point. I think this was used more when skiers performed fewer switch maneuvers. If you've ever arced a turn switch on a pair of skis mounted center you can notice not only the increase in stability from the larger tail, but also the maneuverbility due to the sidecut being more centered, so to speak. Just my 2 cents.

I have read a little bit about how to determine exactly where to mount the bindings, and need some help in making sure I have this correct before finalizing my design.

My understanding is that the ball of the foot should be over the midpoint of the chord, and then the middle of the boot is estimated.

How are others determining this?

Would it be possible to add the center boot location on one of your CAD drawings, and possibly a side view showing the relationship of the camber to the side cut? This would be a big help. Thanks.

I use a simple calculation of area for determining the mounting point. 42% of the area should be behind the boot center for powder skiing. On my Voelkl Gotama this is a bit to much forward for powder but you can carve it well on piste. With my reverse sidecut homebuild i can lean as much forward as possible without making the tip dive (it just slows down). I put the widest point (reverse sidecut) of the ski to the boot center.

Thanks for the 42% number. If you were building a std all mountain ski with sidecut and camber, would you design it so the min width corresponded with the boot centre (assuming the 42% rule) and the max camber was situated at this point as well?

Alex, How did you arrive at the 42% number? I've been measuring skis & moving bindings to evaluate performance & have yet to find a reliable number. I'll apply your 42% to what I've tried so far & see how it compares..... I'm curious!

There was a posting in another area of the forum that suggested a ratio of 200/250 for the area behind/above the binding. So the percent for the tail would be 200/450 = 44%, which is pretty close to the 42%.

hose-man....i sent you a few pm's re surplus fire hose you still may have for sale...can you let me know please. Thanks.

There was an article in a freeskiers magazine some time ago. They said that 42% is the maximum you should go backwards to keep the ski still manageable on the slopes. A more versatile setup is 43-44% percent. We tested the 42% percent on some skis (Rossi B3, Atomic Sugar Daddy, Karhu Jill, Voelkl Gotama) and found that this is a good compromise for freeriding.

The min. width seems to be always a little bit 1-3cm in front of the boot center. But i'm not shure about this...