Exact center of the ski question for shaping skis

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Cadman
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Exact center of the ski question for shaping skis

Post by Cadman » Mon Mar 20, 2017 5:23 pm

I have working on some new shapes and some of the people that I have chatted with always mention everything in relation to the exact center of the ski (total length divided by 2). They want the mid running length on the center of the ski. With tips being much longer than tails these days, I find it difficult to agree that the mid running surface needs to be at the exact center of the ski. They also think that the mounting point should be in relation to the exact center. I also am skeptical about that. I think it has more to do with the distance from the mid running surface. Historically, the ball of the foot went on the mid running surface and the center of the boot should be where the waist is. From size 5 to 12, that distance between the ball of the foot and the center of the boot only changes by slightly more than a centimeter, believe it or not. I don't know if this is still the standard or not with the new tech skis.

Anyone have any suggestions? Maybe what worked and what didn't so well?

burnside
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Post by burnside » Tue Mar 21, 2017 6:16 am

I don't ski, but I've seen this topic pop up a few times. Here's a couple discussions:

http://www.skibuilders.com/phpBB2/viewtopic.php?t=2395

http://www.skibuilders.com/phpBB2/viewtopic.php?t=591

http://www.skibuilders.com/phpBB2/viewtopic.php?t=785

http://www.skibuilders.com/phpBB2/viewt ... 4fe309abca

I know there's been a more in-depth, multi-page discussion that I couldn't easily find. Worth some digging into the older design forum pages. G-Man has some really interesting thoughts on this subject.

Hopefully this helps and I didn't just completely misunderstand what you were asking ;)

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vinman
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Post by vinman » Tue Mar 21, 2017 8:44 am

Those are some good threads. I typically place the waist of the ski somewhere between 53%-56% of the ski when measured from the tip. This depends a lot on what type of ski I'm designing. For powder and freerode umm make the tip a bit longer 54-56% range and for all mountain or carving designs I'll make the waist slightly closer to the tip 53-54% range.
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Cadman
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Post by Cadman » Tue Mar 21, 2017 10:45 am

So are you talking about the tip (widest point) or the forward contact point? Historically the waist was around 55% of the running surface length. It seems like the free riders who ski switch are mounting their ski forward of this point so they can ski backwards so the 42-44% appears to be more appropriate for twin tip free ride. Perhaps the 55% would be for directional skis.
I want to keep the widest point of the tip up off the snow abit so the ski doesn't hook up and then release as the tip vibrates up and down.

By the way, I did some experiments with a Brannock device that they use for measuring shoes sizes. I measured the total length and divided by 2. I then found where the ball of the foot was and then subtracted the difference to see what the dimensions were for different size feet. If anyone is interested in looking at the results, please send me a message and I will send it to you.
Last edited by Cadman on Tue Mar 21, 2017 1:50 pm, edited 4 times in total.

Hannes
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Post by Hannes » Tue Mar 21, 2017 10:56 am

And are you guys talking about the tip of the final ski or are you talking about the tip of the flat template?

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vinman
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Post by vinman » Tue Mar 21, 2017 3:17 pm

I measure this on my initial CAD drawing, so this is from a flat plan view reference.

If I am designing a freeride/BC/powder ski I tend to set the waist back at least to the 55% measurement when measured as described above to give the ski a bit more float on powder. If I want a ski that is more on-piste driven I might shorten this up a little to make turn initiation more of the emphasis.

You can measure this any which way you want. Measure it from a flat plan view using overall length and take a percentage of this, or measure it using a percentage of the running length. A lot of times the difference is fairly small and there are times I draw it both ways and see which drawing looks right to my eye, or even split the difference between the two. There really is no wrong way in my opinion. It really just depends on what you are trying to accomplish with your design. You can always play with your mount location after the fact also.

I also am sure to make when the ski is pressed is that the height of the camber is placed at the waist location of the ski

Not sure if this totally answers your question or not but this is what I think about when i'm drawing skis
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Akiwi
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Post by Akiwi » Tue Mar 21, 2017 11:28 pm

I have found that the binding mounting position doesn't make as big of a difference as I thought.
I have Marker Schizo bindings where you can adjust the binding position over 6 CM. I find that wherever I move the binding to , my body position automatically compensates to the middle point of the ski. There is obviously an optimal position, but our body position can adjust to it pretty easily.
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Cadman
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Post by Cadman » Thu Mar 30, 2017 10:05 am

I used the Marker Schizo also but I find the position pretty sensitive. It depends a lot on how the waist is positioned in relationship to the mid running surface when you design the ski. I have skied on skis in the past that appear to have the mounting position in the wrong place. I keep moving the bindings forward and aft until I find the position that the ski performs the best and then leave it alone. Thanks for the input.
There appears to be a lot of design parameters that make the ski perform different. Such as the length of the blend curves at the tip and tail along with where the wide points are positioned up on the tip and tail. Too short a blend curve makes the ski twitchy or too long makes it harder to initiate or hook up. Having the wide points too close to the forward contact point causes the ski to hook up and release when the tip vibrates up and down. I have found that scaling the ski doesn't work that well. I think there are certain combinations of geometry at the tip and tail need to be used on all the lengths within the family of skis.

Cadman
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Post by Cadman » Thu Mar 30, 2017 10:23 am

vinman wrote:
I also am sure to make when the ski is pressed is that the height of the camber is placed at the waist location of the ski
That is interesting that you use the waist of the ski as your highest point on your camber. I have hand measured a lot of skis and the thickest point on the profile is more at the MRS. In a way, that makes sense since the center of the boot is normally where the waist of the ski is. On the other hand, the ball of the foot is usually at the MRS where you apply pressure to the ski. I guess it is a preference thing.
From what I can tell, there is still a lot of "Black Magic" in designing the ultimate flex pattern. There are so many different ideas as to what makes the ski perform the best. The ski companies keep this secret. Every once in a while a ski comes out that just stands out and I am not sure whether there is a bit of luck involved or some proven theories. My ski right now goes effortlessly into a turn and carves like crazy. I am not sure what parameter made this work so well. I am working on a 109 waist version right now and want to make sure that I get the same results as the 99 waist version.

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Post by mammuth » Thu Mar 30, 2017 2:33 pm

MRS?
Tom

Cadman
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Post by Cadman » Thu Mar 30, 2017 3:55 pm

MRS stands for Mid Running Surface. It is the half way point between
the FCP (forward contact point, where the tip starts to bend up) and the
ACP (Aft contact point, where the tail starts to bend up) on conventional cambered skis. Sorry for the abbreviations.

FEE - Forward Effective Edge (widest point of Tip)
REE - Rear Effective Edge (widest point of Tail)

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vinman
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Post by vinman » Thu Mar 30, 2017 4:51 pm

To be more clear. I make the center of the sidecut and the height of the camber line up in the same location. I place a line at this point. Folks can use that as a reference for where they want to mount their ski in relation to that mark. If they mount on the line then the boot sole center will be at the height of the camber and center of the side cut.
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