'Gamma SL', new design, hope to press mon, thoughts?

[SCHÜSS]

Ok i finally have everything in place, all the materials and the time and the press. After completing over 6meters of pure test cores for composite layup and core layup, this is what i have come up with.

haha and its scary to think i spent $450USD on tests.. ahh homebuild dedication

This will be my third ski. Here are the goals for the ski.

-A Slalom ski.
- A short radius
- MAX grib on ice and hard pack conditions
- groomed runs only
- Alot of rebound.
- good torsional strength
- High end skier ability.
- if you were to compare with a manufactured ski; trying to compare to race stock fischer wc sl and nordica slr.




The sidecut is 115, 64,100 and will give roughly a 14m radius at 165cm.

The shape is modeld exactly from a 07 fischer wc sl.





i want the ski to carve like its on rails, which means max torsional stiffness. i also need rebound which means i need alot of fibreglass under the core. and to achieve short radius i still need it to flex. for full grip i also i still need it to be stiff. haha sounds like i am very demanding.

reasons for the layup composition:

carbon fibre layers times 2. these will dramatically stiffen the ski to a race ski standard.

tasmanian maple- excellent wood for skis. strong, excellent flex pattern.

triaxial fiberglass 3 times under the core, 1 above. My research showed that fibrelgass under the core gives pop. 1 above the core to balance out the ski more. and triaxial cause the 3rd strand improves torsional stiffness.

2 layers of kevlar. kevlar helps the flex out and is great under the core. it is a great compression material. the second layer will have strands at 45º as kevlar strands a very resistant to stretching, placting them in a 45º orientation will help stiffen up torsion once again.

The press.

I spose it would be classed under a clamp press. however if you were to look at it that way it would utilize 64clamps and spread pressure almost evenly.

it is all set up on an steel I-BEAM, and features 5/8 bolts coming out of the ibeam, spaced 8cm apart. each parralell bolt is linked by a steel angle beam to apply all the pressure. wood and alluminium sheet help spread the pressure evenly. we have used this press for the previous 2 skis and the results are perfect. no bubbles or dryspots, no delams. its great.



Oh and the tip will not feature steel edge!!! the edge will run up and rise until about 1cm off the ground and then normal ptex will take over. We found this is still durable and makes our homebuilds alot better looking cayse i cant bend the tip edges very good yet.

What do you guys think? will it work? any problems u may see? too stiff? how will the edges bond to the kevlar?

thanks guys

schuss, revealing the 'Γgamma SL'[/b]

[bigKam]

my goodness.

great write-up by the way -- i like the details, and thanks for sharing.

based on your ingredients, the ski will certainly be stiff. i'm surprised to see so many layers of 22 oz. fiberglass. i'm interested in the result, however. how thick is the wood underfoot? and what are you using to dissipate energy -- that is, vibrational energy?

like i said before, i'm intrigued by the tasmanian maple. sounds like high quality wood. speaking of wood, when you see the species i'm using for my latest pair you might fall 'dead'....

the clamp press sounds very interesting. please post some photos!

i can't wait to see your new creation....

[SCHÜSS]

I will post some photos of the press during the week when i get my cam back.

well with our last ski, we chose not to use any vds rubber or anything, and the end result, not sure if it was the wood> but the ride was suprisingly smooth. However last ski we did use alot of aluminium.

Also my theory is (based on nothing scientific, hehe): its a ski designed specifiacally for carving. so you must push and exert alot of your own energy into the ski. the ski will alomost be in consant flex as it is a slalom ski and its best when kept on edge at all times. so i figure most of the vibrations will be harmonized during the turn? or soaked up in the many layers of composites:D

im not sure to tell the truth, last time it wasnt a problem so this time i didnt plan for it to be one? have you had issues with vibrations?

Also to increase the power to the edge i desided to go ptex sidewalls that will be routed down to about 1mm thickness, (apply them at 2.4mm thickness), theory there being that the core will be as close to the edge as possible, allowing max power transfer, thus giving extra grip, precision and control.


re. to the many layers of fibreglass. well i did a few 1m long tests of the core profiled from 14mm to 2mm and tried different layups of the fibres.

i found the test pices were not much more stiffer if you had 3 layers or just 1!. but i did notice the rebound energy to be alot greater with the more layers. i did a test peice with 3 on bottom and 1 on top and it achieved very good results.

oh and underfoot peak thickness will be rougly 19mm, that includes edges, topsheet etc

kam, do you think 2 layers of carbon will be too much. i still want it to flex!! lol

cheers

schuss

Γgamma SL

[Cadman]

I would guess that you are going to need to eat your "Wheaties" to ride this bronco! I am excited to see how this one comes out. Maybe that 7 foot
Russian who just lost his boxing match would like to take these for a ride.
Just kidding!
I am guessing that you are using the more fiberglass instead of metal to get both pop and torsional strength. Most of the race skis I see have metal on top and bottom. We built a ski awhile back with double layers of thick fiberglass on top and bottom. It was a stiff one. What kind of temperature are you going to be using?

Have at it, my friend! That is what this site is all about. Looking outside
the box!

[SCHÜSS]

I have spoken to alot of people about this design, and there is a possibility it will be too stiff.. and its getting me worried. i dont want it to be soft at all. but i do want it to flex like it resembles a ski still!!

many people here ave the strong belief that core thickness effects stiffness of the ski the most.

At this current stage, we are sitting on 13mm, Do you think it will make it a little better if we make it only 11mm instead. thats a reduction of 2mm. Or will the many layers of composites drown this 2mm reduction into making it insignificant??

Aslo its good to take note that the waist width is only 64mm.... u guys are all pressing big fatties! so my thoughts are that the wood will not make too much diff!

schuss

[Alex]

Very complex composite design - impressive

Two questions regarding your testing:

Did to compare the properties of carbon above and below the core? Theroetically it should be better below the core!?

Do you have some more information regarding the use of Kevlar - where do you see the biggest advantages?

You say Kevlar is a great compression material - under which circumstances does it take compression in your ski?

[BerkshireSki]

let us know how much this beast weighs and final thickness under boot. I would be curious on cost as well with so many composite and epoxy layers.

As for the compression/tension discussion of Kevlar and carbon. It is correct on the diagram with carbon on top (compression) and Kevlar on the bottom (tension). There are more than a few strings on that topic you can search for.

[SCHÜSS]

re alex, yes one of the tests consisted of a 1m length of vertically laminated tasi oak (profiled 14mm at one end down to 2mm at the other), on the top 2 layers of carbon.

The test showed that with the carbon on top, the piece would bend and shoot back to its original state quickly. When the piece is flipped and the carbon is on the bottom, it feels more relaxed.

and my apologies i had it back the front. compression on the top and tension is on the bottom. so when the ski bends during a turn the under side of the ski will stretch and the top side will compress. carbon and kevlar to my understanding are opposites, kevlar does not like to stretch, so when the ski is bending it wants to flatten back out? in the same bend the carbon on top doesnt want to compress, making it also want to 'flatten out'? i think that makes sense. actually now thinking of it, does that make them want to cancel each other out?????

so it works in two ways. The reason for one of the layers of kevlar to be orientated 45º it will be focusing on the torsion aspect of the ski and not the flex as much, and as kevlar does not like to stretch, torsional flex is reduced. Thus meaning more hard pack grip, control and precision in hard pack conditions.

re berkshireski, as i said above you are correct with the kevlar/ carbon properties, i mixed it up in a typo lol. easier said than done!

I doubt the ski on its own will be too heavy. however with its layers and the extra epoxy i imagine it will gain some weight. It will be a bit of a bastard when i put the plate on it tho. lol

The costs are rather high and as i am at uni i really cant afford it! but some how i am. i love makin skis as i am sure every one here does! kam is experimenting with pallets! as a teen the thought of using hi tech materials seems attractive! surely thats understandable! its the same as fast cars and blow off valves!

So we will see how it goes, i would press right now without thought but because of the extra cost involved in bein a high tech wanna be, i want to do my best in getting it right. well as right as it can get in me garage!

so the more critism the better i say

schuss

[powdercow]

I would just like you to encourage you to try this. I would be very interested to see how the additional layers effect the stiffness of the ski. I know that on the soft and stiff bros splat used the same cores and added one layer of fiberglass on top for the extra flex (at least he used to). Either way good luck, this will be a very fun experiment.

[Alex]

Ok - this get's a little clearer.

Regarding you flex/rebound test with carbon on top/below it would be interesting to know if there was a glass laminate on the other side of the core?

Kevlar laminate is indeed not well suited for taking compression (1/5 of Carbon and about half the compressive strength of glass).

Carbon is almoust equal in compression/tensile strength if use bidirectional fabric - if you use unidirectional you can get a 30% higher tensile strenth compared to compression.

If your goal is getting the stiffest sandwich you should use 0° UD Carbon below and above the core.

For comparison a laminate made of bidirectional (woven) carbon has about 50% of the tensile modulus of unidirectional carbon.

For the +/- 45° laminate there is always tension/compression in one layer at the same time under torsional load.

But regardless of my doubts and critism- please go on with your project the way you think. It will be great to see the results!!

[SCHÜSS]

haha i thought i would throw this in:



Interesting when you look at the strand direction layer by layer!

Ok just for an update( will post in journals soon), we have laminated cores and cut out bases. we also made some mods to the press which you will see tomorrow.

Revisions and updates to design:

*we have decided to lower the core thickness from 13mm to 10mm because of fears you will not be able to bend this thing!

*we have some questioned revisions of removing the second carbon, and/or one of the glass layers.

*Kevlar will be orientated at +-70º in the second layer instead of +-45º due to the width of the kevlar cloth only being 1m wide.

its finally coming together.

schuss

[RoboGeek]

wow! Looking at that makes me dizzy!! lol

Good luck with it!!

[hafte]

SCHÜSS, looks like a fun experiment. I thought I would give you some feed back on my experience with The Big Lebowskis, and provide some more data as you progress into your project.

The Big Lebowskis, are about as stiff of a ski as I would ever want. I telemark, but my partner in this would like to try the ski with alpine gear sometime to see if they would tame down some with the added leverage that alpine gives you. They are a great ski on packed groomers and in powder. If the snow is soft and you can plow through they are fun too. I had a couple of really good corn days on them too once the off pieste snow softened a bit. Where I ran into trouble was on ski packed runs where the snow surface is hard and uneven or lumpy. They really buck me around even at my current 210 lb (225 lb w/gear), and take a lot of effort to control. The sweet spot is also very small. If I get behind these skis at all I get put in the “back seat” and a few times all the way to the ground on my butt because I couldn’t catch up and make a required turn. It’s a weird sensation to have the skis accelerate away from you while you’re on them. I have never experienced that before. They make you stay balanced fore and aft or you pay for it more than any ski I’ve been on before.

Here are the specs on the ski.

185 cm long, 134-98-114, 17 mm camber, 160 cm running length
The mount area starts 200 mm in front of the running length center 257mm behind, and is 12mm thick.
The tips taper to 2.5 mm at the end of the running length.
Weight ~8lb 6oz. (4 Kg)

Layup Specs:
Base and edges
VDS on the edges covering the running length
22 oz. triaxial glass
Birch wood core
22 oz. triaxial glass
6 oz glass
CAP/poly fabric and glass tip spacers
18 degree beveled wood side walls w/epoxy coating


The added glass in your skis will make them heavy. Should be good for plowing through crud.

How are you going to get the triaxial glass to fibers run at 90 degrees to the long access? Are you using uni glass to build up the triaxial layers? The stuff I get has the 0 axis running the length of the ski, and would be too short to get the glass in one lenth the way you show it in the picture.

I like the idea of orienting the kevlar 70 degrees to the long access. I thought I read somewhere that would optimize the torsional stiffness... or was that 20-30 degrees? Oh ya watch out for the stretchness of the kevlar when you cut it on the bias. It'll change shape really easily.

Good luck

Hafte

[bigKam]

SCHÜSS: i'm looking forward to seeing the finished product, and of course hearing about how they work. also, the press...can't wait.

the 10mm will definitely help reduce the stiffness. if i remember correctly from my studies that the stiffness of a composite beams depends strongly on how far the different type of materials are located away from the neutral axis... anyway, i would have to check the details -- i could be wrong, as i'm not an expert...

[SCHÜSS]

As with all projects there are delays and problems that come out. We are working our way through the ski building process, we have lminated woods, cut out sidecuts, and to absolute precision, we cut out the bases and attached edges like our other skis. However, citting out the bases and attactching edges was a few days ago.

every thing fit Perfectly together then... now, a few days later one of the bases does not line up any more and is out by over 1cm and you cant 'bend' it back?. what the!!! is this due to them being in an enviroment where in a 24hour cycle the temperature shifts 15º? are they contracting in the cold and expanding in the heat enough times to warp out of line?!

this annoys me as we have decided to cut out another set of bases, but we are leaving it to just before pressing this time.

makes me fustrated and sad:( lol

schuss