Questions for vac bag people

[grandhavenski]

Im doing my first pair of skis now and have a few questions for people. I am familiar with it from doing skimboards and surfboards but see some unique issues with skis.
First off how much Hg do you need do so a pair of skis? Can you sand a radius on your tips/tails and vac your topsheet around it to make a cap edge?
I also have a question about flex. I am doing some twin tips that are like armada alpha 1's only wider, like 185mm x 90mm waist and 120 tip tail. I have a poplar core and maple sidewalls and plan to layup 19oz triax on top and bottom with a 2" unidirect carbon. Oh and carbonnized bamboo topsheet. Is that going to be too stiff?

[sammer]

Your questions have been asked and answered numerous times on this forum.
Read everything!!
It might take you a while!

To answer;
More "hg = more pressure, you can get away with 25"hg.

How thick is your carbonized bamboo?
You might be able to get it to flex into a cap.
Try a sample.

Ski stiffness is mostly attributable to your core thickness.
Read this
http://www.skibuilders.com/phpBB2/viewtopic.php?t=2701

Also if this is your first pair don't waste your carbon.
Save it for the next pair.

sam

[grandhavenski]

thanks,
I read alot of the stuff but maybe I missed something in my search criteria. Anyway the biggest question I had was about the pressure.
Anyone have any experience with twin tips and this kind of construction. I ski pretty hard and am worried about breaking them. I have broken a few pairs of k2's and a pair of 92mm ninthwards which were pretty stiff

[MontuckyMadman]

how/where did you break the skis?
If it was from park it will happen no matter what type of ski you build.

[grandhavenski]

the k2s broke at the rear binding mount, one during urban rail, one during normal table landed backseat. the ninthwards broke on a table that i overshot and just landed hard, broke wierd though, edges blew out and the layers just peeled off one another. like exploded from the inside

[MontuckyMadman]

Park skis are softer on the average. If you make a ski like a 2x4 your more likely to break yourself than the ski.
There is no ski that will last forever on hard snow landing in the park. Its juts the way it is.

Ninthwards are pretty stiff from the few that I have skied. The heavier the composite also the more the fibers will bear the load vs the core.

Skis fail at binding holes and break at the tail when you land backseat even in soft snow.

I would make a stout core but you will sacrifice performance in the park. Its a trade off between soft ski park performance and durability.

If possible I might consider a hard wood core but the ski will be quite heavy and swinging that weight in the park will be harder. Again a trade off.
I find we get very good strength to weight ratios for different typed of skis with mainly poplar but stringers of maple running where the binding screws go in.
Try a linear taper core profile on center of 2-13-2 with 10cm tip and tail spacers as a start if all poplar. So a 165cm core. Thin slightly when adding more maple. It always feels like park skis have that flat spot and the flex point is farther forward making the tip and tail kinda soft. The overall core profile would be thinner with a substantial flat spot of say 40cm or more. say more like a 2-11-2 profile.
No way to know till you try it. FYI i have not made a symmetrical park ski nor do I ride park anymore.

[grandhavenski]

thanks montucky
im definatly not worried too much about breaking them but if they are too sloppy/ or stiff i wont ride them much. Im taking your advice on the core but going 3-12-3 because the resin im using is pretty snappy stuff. Ill post what i end up finding out.