Kaweah: rubber, aluminum, steel, glass, and wood

[bigKam]

the Kaweah - if all goes well, Kaweah will be another new ride. (it's being squished as i type this).

this is the second version of Kaweah -- the first pair (with completely different graphics) came out of the press two days ago and ended up in the trash. in my usual hurried-state, i did the layup omitting my patented alignment process, and was careless with a few other steps. bad idea. the result: everything shifted, up to 2" (50.8mm)! i guess you win some and you lose some. i'm not even going to bother with removing the flash. instead, version 1 will hang as a reminder.

30 minutes after the fact, i cut new base and profiled a new core (this time using maple; version 1 was pine (w/knots) + fir + polar).

now i'm interested in hearing about this: what combination of materials (layers) are builders using in their designs? also, please comment on ride characteristics. to spark a conversation, here's what i'm currently experimenting with:

goal: damp ride, especially at high speed.
objective (it's a hypothesis) to achieve the goal: use a combination of rubber and metals (combined with wood and glass, of course).

last month i used these materials and the result was a considerably more damp ski than the traditional wood + glass design. in this first design, i completely covered the base material with VDS rubber. now i decided to cut back on the VDS, adding instead patches of thicker rubber immediately above the base material and on top of the core. here's the basic structure of Kaweah (top to bottom):

epoxy: West Systems (205 hardener)
----- top --------------------------------------------------------------
- clear Ptex topsheet
- thin cloth (graphic)
- two layers biaxial (6oz) fiberglass
- maple core with patches of rubber and tip/tail spacer (see photo below)
- strip of steel on 22 oz. triaxial fiberglass (see photo below)
- patches of aluminum and rubber -- note rubber on tips (see photo below)
- base material with VDS rubber over edges.
----- bottom -----------------------------------------------------------

so, what are you using and how does it ride?


rubber and aluminum


steel (50 um thick (0.002")) on glass

rubber (925 um thick (0.037")) on wood (recess in wood for rubber)

topsheet

[SCHÜSS]

Hey looking good! i hope this pair works out well! interesting layup too especially with the alluminium.

I used allu with our mark 1 SL and found that over time (usage time) the ski progressivly lost camber, it got to the point where it was achieving negative camber. however we used ALOT more allu than you have.

Currently i am looking to press our mark 3 version. i am just regoing over the pressing method and press making sure i will have no errors on the day. (we are perfectionists, and in our mind we are pictuing a perfect ski! we dont want to be dissapointed... or atleast minimize it!) we wont achieve it yet but we are doing everything we can to achieve it.

the mark 3 schuss SL is actually an entirely new construction.
(mark 2 was more of a revised modification)

here is how it goes:

purpose: Carving. Properties: beyond exceptional ice grip, short radius. stiff but alot of rebound. Dimensions: 115-64-100 *plans to build one with a wider waist, to create the perfect ski. 143-80-121

layup

clear topsheet
2x2twill carbon fibre
2x2twill carbon fibre
12oz fibreglass
tasmanian maple core (laminated vertically 19mm intervals)
12oz fibreglass
12oz fibreglass
12oz fibreglass
kevlar
base+edges w/ptex sidewalls

Will be documenting it all on vid. so pics will come soon.

mark3 SL will also be combinded with a Vist x-balance World cup slalom plate and Fischer Z17 bindings.

Only worry i have is getting the tip right... it was the dodgy part of the last ski and i am having troubles working out a way to make it precise and clean. especially with bending the edges.

Thoughts and comments would be the best!!

Also i bought a skibuilders t-shirt today!! woooooot!!

schuss

[bigKam]

schuss: good to hear you're getting an SB shirt. your support is much appreciated.

you have a nice layup structure. i'd like to get my hands on the tasmanian maple . are you using triaxial glass? what's weight of the kevlar?

the Kaweah is done:




note the rubber and how the wood was cut to accommodate it.


there are some air bubbles beneath the topsheet. it feels softer than expected -- like a noodle; it better be waist deep when i run them for the first time. core was 9mm underfoot. i should have added another layer of glass. the skis feel relatively light (don't have a scale to get numbers though). qualitatively speaking, "claw" test says "damp". i'll have to ride them to see.

[RoboGeek]

love the graphics

mount them puppies up and get ridin'!!!

[G-man]

bigkam,

I've been doing a lot of ski testing lately (my own skis), and I have been trying to pay attention to the dampness aspect of the different skis. To be really honest, I have a hard time assessing that quality. I don't really get any discernible resonation that feels undesirable, nor do they feel 'dead'. I find myself wishing that I had something to compare to, like a ski that had a solid reputation of being too harsh and one that was too limp. It just seems that determining the 'dampness' of a ski may be even more subjective than determining the 'pop' of a ski... how do we put a number to how damp a ski is? Sure, I get a bit of harsh feedback from a ski when I'm skiing early morning frozen corn, but if I were on a ski that made frozen corn feel comfy, that same ski would be pretty unresponsive when the snow began to soften up once the sun hit it. I wonder if anyone else has a difficult time assessing dampness.

Regarding my lay-ups, I'm tending lately to put a bit more 45/45 bi-axial fabric and a little less longitudinal fabric in the mix. I've noticed that with all of my skis, if I push them hard enough in the conditions that I designed them for (basically soft flex for soft snow and firm flex for firm snow), I can get them to set up this odd longitudinal axis 'shimmy' kind of thing. It seems that the tip and tail edges will hold until the forces reach a certain level, then the tip and tail alternatively lose purchase, causing the ski (usually the trailing ski) to whip back and forth just a bit. I have a tendency to really get over my rear ski, so I don't think the shimmy is happening because of inadequate weighting. Also, the shimmy doesn't happen until I really push the skis holding ability. So, I'm now tending to build the skis with a greater focus on torsional stiffness, while trying to maintain a smooth round flex. I'm currently assembling the lay-ups for skis as follows:

top sheet with no graphics (still trying to limit/isolate potential delam factors)
two layers of 12 oz. 45/45 biax.
one layer of 6 oz. uni.
pine core
two layers of 12 oz. 45/45 biax.
one layer of 6 oz. uni.
usual VDS
base

Depending on how heavy and on how longitudinally stiff these skis turn out, I may omit the upper uni layer (as it appears that you are now doing), as the 45/45 fabric above the core will still add some degree of longitudinal stiffness.

For now, I'm just sticking with the uniform longitudinal flex scheme. Once I feel like I have a pretty good baseline feel for it, I may start playing around with softening up or firming up the tip and tail sections (longitudinally) so that I can more 'logically' assess some of the differences these changes might impart to the performance of the ski. I think that firming up the torsional flex may help to improve performance in terms of my current shimmy issues. In actuality, there are so many on-snow variables from day to day, it's somewhat difficult to objectify much of this ski performance stuff. I know! ... I'll just build a parameter controlled indoor ski testing facility!. There must be a DIY on-line forum for it somewhere. I'll goggle it!

G-man

[bigKam]

G-man:

in some respects, qualitatively speaking, it's difficult to assess damping. it's complicated and there are many factors such as snow conditions, sidecut, length, what a person had for breakfast, etc.

but i'm thinking there's a simple method (by approximation) to determine the amount of damping for a ski (out of snow) using analysis tools for dynamic mechanical systems - a ski is a dynamic system. i've been meaning to try this experiment to determine rough numbers for how "damp" a ski is. this approach is nothing new -- in fact, it's used extensively to assess the dynamic behavior of many mechanical systems: vibrating cantilevers, accelerometers, etc. John Howe of Claw Skis (he used to work for Head, i think) has done similar work in this area.

anyway, here's what i'm thinking: damping is related to the amount of energy dissipated (converted to heat) from a system when it's perturbed. for example, if you smack a ski (using that sophisticated epoxy pounding aparatus of yours, for example), the ski will vibrate and at some point come to rest. the way it comes to rest is related to how damp the ski is -- like how fast the energy was removed and the nature of dissipation. it can get complicated, i agree, but we can simplify by modelling the ski as a combination of three elements: mass, a spring, and a damping element. below is my simple (linear, 1-D) model which consists of mass, a spring, and a damping element. the objective would be to determine the value "b" for each ski and use that as a comparision. the math isn't important -- only there for completeness and to organize my thoughts.



anyway, for each ski, if we can determine a rough number for "b" and then collect qualititive data (by skiing), maybe there's a correlation, maybe not.

here's the simple experiment: clamp a ski to a big table, smack it hard (with a big stick). this will essentially deliver an impluse input and what the scholars tell us is if we can measure the response (vibration) over time, we can figure out damping by relating (curve-fitting) the data to the above model. ta-da: we have "b".



it would be neat to collect this kind of information for various layup structure and then have discussions over a cup of coffee...

i find your layup order interesting. thanks for sharing!

[endre]

This looks interesting!
I did some testing of vibration once, basic principle of John Howe. I even built a machine for it, but I never understood the results, so it is just rusting away. Guess I could get some help from you guys.
Unfortunately I have to go away for a week, but I look forward to the followup.

[thetradwoodboat]

fantastic site! i've been listening in for quite a while, absorbing info and building skis.
i am starting in on pair number 4 now and dampness has become a major focus. the dampness comparison between my own skis and a pair of karhu rox i've got, is like feeling every snow crystal and riding on silk.the karhus are infinitely more damp. to my mind it is more a comfort issue than preformance, as i love the way my own skis ride for the most part ( biased?)
is there a general consensus that the addition of vds softens the overall flex? my number 3 pair, meant to be for firm groomers i.e. stiffer, used a hardwood core, 22 oz triax top and bottom with vds just above the edges. i was real surprised to find that they were a lot softer than the previous pair made with a spruce core and no vds.
i intend to add carbon fiber top and bottom on this next pair, with the vds and not change anything else. baby steps.
i do think adding aluminum is probly the answer to good torsion and dampness. i'll be trying that soon too, sadly there is so little time. i can feel the new england winter starting to melt away.
i'm curious as to what you guys are using for aluminum stock?
an engineering buddy said recently that wet sanding the aluminum with epoxy during the layup process prevents oxidation, making adhesion much better, sounded like a good idea.

nate

[cliffhuckster]

i have talked extensivelly to my local ski shop about dampening, core options, camber, tip profile, basically the essentials of a ski. i am currently skiing on rossignol sickbird's (with alpine bindings-sorry-my other pair of skis flew off the top of my car in november when i didnt lock the racks-this sickbirds were a cheap replacement). they are sort of heavey, and they tell me that's because the rubber in the ski weights it down. and they are pretty soft but they seem to stay damp at higher speeds on more consistent snow ie:groomer/untouched powder. but when i am skiing through crusty slashed up inbounds leftovers they seem to not perform very well. i think it may just be the softness of the ski, because as i start to put on the brakes they lose their vibrations pretty quickly.

when i told them i was going to build skis, what they told me is that rubber dampens a ski, but makes it heavier and doesnt stiffen it. metal (they told me to get titanal-i think its just higher end aluminum) on the other hand, will dampen a ski keeping it lighter than a rubber filled ski and also stiffen the ski. so, according to them, rubber=damp,usually soft (depending on core),heavier. metal=damp,usually stiff (depending on core), lighter. the metal ski will still be heavier than a ski with fiberglass, but to put in enough rubber to equal the dampening effects of metal would make the ski very heavy.

and your skis- they look awesome! its great to see a complete write up of a ski that experiments with different materials. however, if i would have built them i would have tried to keep the core more consistent. the rubber strips that you put laterally might create "weak spots" in the core that act as hinges when your ski hits bumps. in my ski building experimentation, i would rather put stringers of rubber and aluminum going with the length of the ski. who know though, maybe im wrong. these skis could work great because the aluminum and rubber create an even flex that is great for all conditions. its great to see an idea like this. i would have never thought of putting rubber strips in that way. well, good luck and tell us how they ride.

[G-man]

bigkam,

I really had a great time reading your last post. Seems, though, that most everything that I get interested in now-a-days leaves me wishing for a better math background. It's great to hear that there might, indeed, be a way of attaching a meaningful number to the damp factor. Lucky for me that I have a good friend who is a retired structural engineer (designed big composite aircraft)... he's really good at helping me to understand things that are normally way over my head. I certainly do hope that we (skibuilders.com) can get this damping analysis thing going. Maybe someday I can objectively ride a really damp ski and then ride a really non-damp ski. Maybe then I'll be able to tell that there's a difference... except that by the time I get the skis switched out and get back up the lift for another run, the snow conditions will probably have changed But at least I'll have some real lab data to believe in, eh.

thetradwoodboat,

Glad to have you aboard. I know what you mean about so little time... what little winter we did get in the north Sierra (last week) is quickly melting away this week... geeesh. Regarding laminating aluminum with epoxy, the rational for abrading just prior to lay-up is to remove existing oxidation (don't forget to wipe well with acetone after sanding). The aluminum begins to re-oxidize immediately after sanding, so it's important to get some resin on it really quickly. Non-oxidized aluminum (high surface tension) bonds really well with epoxy, but a little bit of oxidation can severely effect bond quality. There's lots of aluminum/epoxy bonding info via google, if you want to check it out.

G-man

[thetradwoodboat]

thanks for the welcome.
it may be minor but i just wanted to clarify. my engineer buddy's main point was to use the epoxy itself as the wet in wet sanding, in order to keep the aluminum completely sealed off from oxygen, not wiping it off at all, then add the aluminum to the layup. does sound messy to be sure, extra grit and all, but that to me was the interesting part of the technique.
i'm wondering what most of you are using for aluminum? is simple flashing going to work or is it too thick and soft? are there other options aside from going as far as titanal?

[thetradwoodboat]

big kam, i was very interested to see that you are stopping the core completely at tip and tail then adding solid spacers javascript:emoticon('8)'), seems like a great time saver over cutting the core back a half inch around the edge and fitting a u shaped spacer, what is your opinion of change in strength, performance etc.? i think i'll have to try it.

[G-man]

thetradwoodboat,

Ooops. I'm glad that you did clarify. I didn't read your post carefully enough and missed the 'sanding with epoxy' part. Interesting for sure. Personally, I haven't used aluminum (yet), so I can't help out in that area.

G-man

[davide]

I visited a ski test laboratory months ago. They had few downhill worldcup skis, with an alluminium plate glued about 20 cm from the tip.
The guy told me it is for dampening: just cut a 3X20 cm plate (3 mm thick) and glue it on the ski with a double side tape. The plate should be located around the first harmonic node (usually 30/40 cm from the tip).
He told me vibrations are degcreased of 50% (measured).
Using rubber over the whole lenght damps not only the 1st and 2nd harmonics (as the plate does) but also the higher frequency harmonics. This is bad, because the ski will fell "dead".

[bigKam]

Davide:

your comments are very interesting, and they make sense. now that i'm thinking about it, the first and second modes are rather important in terms of making a ski feel alive..

a few ideas are brewing in my head now...

big kam, i was very interested to see that you are stopping the core completely at tip and tail then adding solid spacers javascript:emoticon('8)'), seems like a great time saver over cutting the core back a half inch around the edge and fitting a u shaped spacer, what is your opinion of change in strength, performance etc.? i think i'll have to try it.

it definitely saves time, and wood. the strenth may be compromised, unless there's sufficient reinforcement -- note: i used nothing special but glass. but i'll test. if i knock out my teeth then perhaps it's not such a good idea...