asymmetrical ski problem

cashat8500 · Post by **cashat8500** » Tue Jun 21, 2011 7:49 pm

This is my first post. Have been reading this exciting site for some time. I have my press built and now am going to start the mold. Of course this forces me to contemplate the ski design. There are so many variables and directions to take them and in many regards an art as much as a science, that it's a little overwhelming. This is what I've come to so far...I plan a medium fat ski with an early rise in the tip and a conventional tail. Since I do not plan to intentionally ski backwards, ever (I'm an older guy, O.K.), I see no reason to rocker the tail. I haven't applied exact dimensions yet, but let's say the rocker starts at 12" back. Drawing the camber arc from here to the tail creates a centerline that is way to the rear of the center of the ski (what with 12" of rocker plus a tip length dangling out front). I've read here that a good rule of thumb for binding location is 54% from tip contact point. If I apply this to my design the binding will be way to the rear. If I apply the 54% at the tangent point of the tip radius then the binding will be way forward of the apex of the camber. Does anyone have experience/ideas on this problem? And also thoughts on the design? Thanks.

MontuckyMadman · Post by **MontuckyMadman** » Tue Jun 21, 2011 8:11 pm

I go 55% from tip of ski measured in a straight line or tape.
This will usually, if designed correctly, put the center of my size boot with the narrowest part of the ski or center of the sidecut. Additionally I will try and put the high point of my camber profile to be near the ball of my foot of slightly aft of that.
It depends on where you taper of your side cut starts, in the tip and what type of arcs you are using and the amount of camber you put in affects where the contact points will be.

I would start with a few known things before you go forward.
What waist ski do you want?
What type of running length are you looking for?
How much ski do you want out in front of you?
What will this ski do, condition and terrain wise?
Camber profile will be dictated by allot of these factors I have found.

sammer · Post by **sammer** » Tue Jun 21, 2011 8:34 pm

The high point on your camber arc should be close to the waist of your ski, eg; the center of your sidecut arc.
With just a tip rocker it's not really possible to have a nice round arcing camber.
It's a hard one to visualize, but the rise from tip contact point to ski center has to be steeper than tail to center.
It's simple rise over run.
Try to keep your camber to a minimum, 1or 2 mm is lots for a powder ski.

The fact is, if the highest point of the camber is near boot center you've already moved the high point back 50-60mm from the center of your ski.

Also remember that, regardless of where your rocker starts, when you lay that ski over you want to be close to the center of your effective edge.

Go down to your local ski store and look at some skis.
K2 sidestash are pretty similar to what your describing.

Have fun with it and don't over complicate your 1st few pair

sam

cashat8500 · Post by **cashat8500** » Wed Jun 22, 2011 8:36 pm

So is it true generally that you want these points to line up; apex of the camber, the waist, the 55% mounting point rule(roughly)? If so, then I need to back up and start with the side cut design.
MM. Waist? Probably around 105, I don’t want too much ski to wield around yet. Starting cautiously. Running length? Contact point to contact point, right? Currently, I ski the Salomon Lord which has 144cm and it feels pretty good. How much ski out in front of me? I don’t know how to answer that. What will this ski do? This is a great question. I don’t get to ski powder that much. But, usually I can find some off in the trees. So I have to ski the mountain between these spots. When I do get deep stuff I want to float like a butterfly. Also seems that I spend a lot of time in crud and heavy snow, I want to be better able to cut through this stuff. Am I expecting too much out of one ski?
Sam. I understand now that I can move the apex of the camber to where it needs to be and let the arc accommodate that. 1 to 2 mm camber? I had planned on 10, ha. My thinking is that I need healthy camber to ski groomed and hard pack, yes? Also, I wanted the rocker tip to ski powder. Am I trying to design something that won’t work? Now then, the effective edge is the length of edge that is engaged in snow(when edging of course), correct? This means, to me, in powder the effective edge starts at the bottom of the tip. But in hard pack it starts at the beginning of the rocker. Once again, does this ski make sense? Your advice to keep it simple is looking better all the time.
Thanks guys.

MontuckyMadman · Post by **MontuckyMadman** » Wed Jun 22, 2011 9:02 pm

Product Specifications for Salomon Lord Twin Tip Skis 2011

Gender
Mens
Bindings Included
No
What Binding is Included?
None
Binding DIN
N/A
Binding Weight Range
N/A
Twin Tip
Yes
Race
No
Alpine Touring
No
Waist Width
86-95mm
Tip/Waist/Tail Widths
128/87/115mm (@ 177cm)
Tail Profile
Twin
Rocker
Tip Rocker/Camber
Turn Radius
16-20
Actual Turn Radius @ Specified Length
17.4m (@ 177cm)
Used
No
Titanium
No
Construction Type
Cap
Core Material
Wood
Special Features
Edge Armor
Warranty
One Year
Skill Range

Advanced - Expert
Model Year
2011
Product ID
163950

Product Features for Salomon Lord Twin Tip Skis 2011

50% Groomed - 50% Un-Groomed
Edgy Monocoque Construction
Full Wood Core
Total Edge Reinforcement with Edge Armor
Rocker 210mm

This mine as well be a park ski to me.
solomon skis are very weird to me.
Put a bunch of rubber in there and yeah you will want camber.

skidesmond · Post by **skidesmond** » Thu Jun 23, 2011 3:11 am

Considering the type of conditions you normally ski, 10mm camber is fine. The ski you're trying to make is doable and not out of your reach.

Keeping it simple for the first pair or 2 is good advice. From what you've said so far, making it rocker is the only thing that could complicate your design but, if your mold is made correctly it shouldn't be a problem.

If you like the Salomon ski, try making your first ski after that design, then you'll have something to compare it too.

But yea, soooo many variables.

vinman · Post by **vinman** » Thu Jun 23, 2011 8:47 am

Shouldn't it be 55% of the running length instead of 55% of the total length? Especially when we are talking about rocker?

Am I thinking about this incorrectly? Wouldn't a long lo rise tip and tail mess up this calculation in comparison to traditional camber skis?

For me with a running length of 1080 on my current design on a 185 cm ski, 55% RL is equal to 6 cm back from center vs 55% of total length being 9 cm back from center.

ski length 1850mm400mm rocker tip and 370mm rocker tail
running length 1080 with 3mm positive camber
true center 925mm
55% running length at 984mm (59 mm set back)
55% true length 1017.5mm (92.5 mm set back)

is my math wrong or am I thinking about this incorrectly?

sammer · Post by **sammer** » Thu Jun 23, 2011 6:40 pm

cashat8500 wrote: This means, to me, in powder the effective edge starts at the bottom of the tip. But in hard pack it starts at the beginning of the rocker. Once again, does this ski make sense? Your advice to keep it simple is looking better all the time.
Thanks guys.

This statement is not quite true.
Your rocker, if properly planned, should become effective edge when you lay your ski on its side during a turn.
The plan would be to match your rocker to your sidecut.
Your ski will turn with less effort, you don't have to pressure your tips as much, as the rockered section is already bent.
Hope this makes sense.

I'm sure someone else can elaborate more.

vinman: your math looks right to me although I've never really measured it that way.
I measured my boot. Ball of foot on ski center (of running length), boot center is X distance from from ball of foot.
Sidecut setback and high point of camber end up somewhere closer to boot center when I draw up a ski. (usually about 65mm back)
Once again I hope this makes sense.

sam

cashat8500 · Post by **cashat8500** » Thu Jun 23, 2011 6:46 pm

Sammer you are so astute. The K2 Sidestash is an excellent match for what I have in mind. The K2 website tells alot about the design, just not everything. Doubt if I can copy the 2 layers of Titanol and the Hybritech sidewall, whatever that is. Any ideas how to imitate the Titanol?
I had an adjustable mold design figured out when the ski design was conventional. But now with rocker tip and asymmetrical camber it seems an adjustable mold isn't feasible. Anyone tackled this?
Thanks to all, I learned alot with this exchange.

sammer · Post by **sammer** » Thu Jun 23, 2011 6:57 pm

Don't worry about titanal. Just make a conventional ski. wood, fiberglass, epoxy, maybe tip/tail fill.
Keep your first few simple.
The more you complicate your layup and design the more chance you have of failure.
And you will have failure (everyone here has a story or two)

Just keep at it but start with the basics.

sam

cashat8500 · Post by **cashat8500** » Thu Jun 23, 2011 7:00 pm

[quote]Your rocker, if properly planned, should become effective edge when you lay your ski on its side during a turn.
The plan would be to match your rocker to your sidecut.
Your ski will turn with less effort, you don't have to pressure your tips as much, as the rockered section is already bent.[/quote]

Ooooooh, I see. I can visualize it, but that's some fancy math.

sammer · Post by **sammer** » Thu Jun 23, 2011 7:06 pm

Not really just keep your rocker arc less than your sidecut arc.
The closer you can get the two the easier it should turn.
At least that's the way I envision it.

sam

maximegb5 · Post by **maximegb5** » Sun Jul 24, 2011 9:39 am

Worst case senario: your rocker is too small and your tip still need to bend a little when turning, which does not matter as the ski will still be easier to make turn than a traditional camber profile. Or your rocker can be too bent and your tips will not touch snow unless you bend your ski a LOT, which will make it ride like a snowblade on the hardpack but with some profficiency in powder. IMO just go with your gut feeling, and as long as they hold together you'll manage to ski them and have fun on the first imperfect pair a couple of days

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