An ultralight (K skis by the Ski Lab)

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bigKam
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An ultralight (K skis by the Ski Lab)

Post by bigKam »

I'd like to share some new work.

This past spring while ski touring with some good friends in the high Sierras, the idea of building a light ski came up. You see, some of my friends will not ski on my skis simply because they are not light enough. Whatever.

But being an avid backcountry skier myself, I can appreciate light skis, especially for those long long routes. So it got me thinking and since that day I have been constantly thinking about building the lightest ski possible. It has consumed me, to be honest.

Anyway, I spent some time looking at some of the 'light' skis out there and found many that I wanted to mimic in terms of weight. One ski in particular is the Movement Logic X-Series. With a length of 168-cm and dimensions of 125-88-115 mm, a pair weighs 4 lbs 6.5 oz (2000 g), so that's 2.20 lbs (1000 g) per ski!! Wow.

But seriously, how hard could it be to make something with similar shape and as light? Well, it's actually not trivial, but certainly possible for a D-I-Yer (e.g., see below).

So I got to work and carefully selected materials and crunched some numbers, then double and triple checked my calculations. You see, making it light isn't really the problem; the challenge is making it light and still strong enough to last more than one run. Light skis are usually used for long trips and the last thing you want is for a ski to break while you're descending a 4000 ft. couloir miles away from your car. A failure means a long walk out, at the very least.

So I made three pairs, all with length of 170 cm, dimensions of 127-93-115 mm, sidecut radius of ~20 m; they're slightly longer and wider than the Movement Logic X-Series. These skis were designed for a good friend S. Wild who is very weight conscious.

We named them the K Wild Jellys -- just a random name we both agreed on.

For the first pair (sorry no photos), I got a weight of 2.49 lbs (1129 g) per ski. The first pair was bare minimum and it was ugly, but it turned out pretty good. Because the first pair was so ugly, I decided to add some graphics, and thus the 2nd and 3rd pair came out looking more pleasing. By adding graphics I had to be more creative to shave off weight to compensate, but the final result was a weight of slightly over 2.5 lbs per ski. Not bad and they were not that ugly, so here's one pair:

Image

Image

What are the ingredients? Well, who wants to guess? ;) I can tell you the basic list: wood, some metal, some rubber, steel edges, ptex, other plastics, fiber glass, carbon fiber, and epoxy.

I think it can get light than this. So for a fair comparison, I'm using this length and shape as the benchmark for more future versions, and my personal target for 'ultralight skis' is 1.99 lbs per ski! Let's hope they don't break....
Last edited by bigKam on Tue Jan 03, 2012 10:55 pm, edited 1 time in total.
OAC
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Post by OAC »

1.99 lbs(~900g)...I'm on! (The breaking might be an issue...)

Sweet skis!
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Post by skidesmond »

Kam, how did you get the cap made using your press? They look fantastic. Let us know how they ski. I'm interested how damp they will be as well. Do you plan on doing in-house testing before you ski on them?

Thanks
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Post by bigKam »

@OAC > "1.99 lbs(~900g)...I'm on! (The breaking might be an issue...)"

Nice! Now the fun begins.

But I think we should set some rules, guidelines, etc, because like I said, weight is not the challenge because one can hit that target, say use balsa wood and leave out sidewalls and use paper for the topsheet and just one layer of fiberglass, but a ski like that is not skiable and it won't be durable, either. The final product should look nice and work, in my opinion. In other words, a true DIY ultralight should compare to the tried and true light skis on the market; the key words are "tried and true" and let's add "respectable" too. In my opinion, the Movement Logic X-Series is not by accident. Some nice engineering went into that ski.

Anyway, I'll jot down some guidelines later today and we can all share and figure out what the boundaries are. I'll post the DXF file for the shape, but again we can tweak that as well if needed. This way it will be easy to compare each others' work.

@skidesmond > "how did you get the cap made using your press? They look fantastic. Let us know how they ski. I'm interested how damp they will be as well. Do you plan on doing in-house testing before you ski on them?"

Yes to the cap. The topsheet is standard PBT and Chad at Coda printed it for me (thanks!!!) What you see above is my third cap ski. The first test ski came out great. The second was nice too. The cap is not my idea; I've heard about it done in a few other places, using all sorts of techniques. I can't say for sure that my process is the same as others because I've never really seen it done in person elsewhere, but I'm sure it's similar and as expected it does require precision. I put a little thought into the process, and like most things, I went through the numbers. But as we all know and I'm now a believer, it requires some sort of female mold and again, precision! It's not the easiest thing to do and it can be inconsistent if your process is not dialed, but if you can afford the tooling, then it's a nice option to standard sidewalls. A CNC helps though!

In terms of durability, it can be an issue if you don't get a good seal or if there's not enough material above the edge. What I've done is more of a hybrid --- cap + a thin sidewall. I think people in the industry call this a 'half-cap' or 'hybrid' sidewall. I'm working on a few other approaches to this because I want perfection. The only problem I have is I make custom skis so I'm not sure if the cap is the right choice because again, it requires precision.

I will be doing in-house testing. One pair is going in the mail today to S. Wild for field testing. I will be field testing myself and also failure tests. I'm curious about a few things and want to know what the main issues are and challenges.

Regarding damping -- we'll, as I've pointed out, damping is not that simple. I believe these skis are relatively damp, but I'd have to strap some sensors on it to measure the loss factor. I know what needs to be done to enhance damping, but there's a tradeoff between that, weight, and failure strength. Right now I'm focusing on weight, strength, and durablility.

I'll let you know what I find out..... Boy, this is fun but like the rest of ski building, it's going to consume me again and again and again....!
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Post by skidesmond »

I agree damping can be a tricky thing. I'm curious though since they are so light if they will chatter on hard pack. Probably not much of a problem/concern for you guys out west but it is in the North East.

So now I get how you did the cap, tricky stuff.... simple in principle but not in execution. Looks like it's dialed in. Very nice.
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Post by Richuk »

SD - have you tried using 1 inch kevlar tape down 3/4 length of the edge set? Relatively expensive approach, but effective!

Working through a design like this is a great approach - it would be cool to gather the feedback from across the world about a very similar idea. You could go crazy and piggy back of this project: http://www.pushsnowboarding.com/. The hardware is cheap, the wiring is simple and the coding is OK ... not my forte. Not the only approach, but the cheapest.

I'm not able to join this time, although I have a few ideas. Have you guys had a look at skitrab, 700 - 800g?
Last edited by Richuk on Tue Jan 03, 2012 4:26 pm, edited 1 time in total.
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Post by skidesmond »

Richuk wrote:SD - have you tried using 1 inch kevlar tape down 3/4 length of the edge set? Relatively expensive approach, but effective!

Working through a design like this is a great approach - it would be cool to gather the feedback from across the world about a very similar idea. You could go crazy and piggy back this project: http://www.pushsnowboarding.com/. The hardware is cheap, the wiring is simple and the coding is OK ... not my forte. Not the only approach, but the cheapest.

I'm not able to join this time, although I have a few ideas. Have you guys had a look at skitrab, 700 - 800g?
I don't understand what you do with the Kevlar. Are you saying to wrap the kevlar over the edge to give it a cap appearance?
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Post by Richuk »

Just responding to your point regarding 'dampening' SD. Include it in the lay up, over the vds. Lay it flat, but slightly away from the edge, so it is within the boundary of the ski edge.
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Post by skidesmond »

Rich, Ok thanks.
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Post by bigKam »

@Richuk -- yes, I know Ski Trab, but which ski are you talking about, because when I last checked the skis in the 700-800 gram range were not that wide, about 96 mm at the shovel and 64 mm at the waist?

http://skitrab.com/en-us/c-5-ultra-ligh ... d-cup.html

Here's something that's comparable, slightly narrower, but it's 1360 grams (for the 171 cm) though...

http://skitrab.com/en-us/c-9-piuma-evo/14-polvere.html
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Post by telehead »

Nice work Kam!! The core looks very thick at the center, what is the dimensions of the core, and do you have a platform underfoot? I really like the way the top edge line fades into the tip and tail. Very clean!!! Do guys really ski on 170's? Or are they for a girl??? LOL!!!
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Post by bigKam »

@ telehead -- core is approximately 11 mm (0.433") underfoot; the shadows in the photo makes it look thicker than it is. The first and second pair I made were 12.5 mm (~0.5") underfoot. If the skis were for me I'd go with 176 cm, but the request was for 170 light touring skis, so 170 it is. Silas is one mean man and he eats whole chickens for breakfast.
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Post by rockaukum »

Kam, skis look clean! Like the graphics too. Ask Max about them when you see him next.
Patiently waiting for snow....
ra
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Post by bigKam »

Hi Everyone,

OK, as promised here are some files for the shape of the K Wilds:
Image

[DXF file, click here]: please note the size of the ski in the file so you get the units right, so convert accordingly.

[PDF file, click here]: you should be able to print this on multiple sheets of paper then use as a template. At the top of the page there's a 25 mm reference line, so scale accordingly to get the correct size.

I'll write more later....
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Post by Richuk »

Just another point of reference Kam!
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