I have been setting up my molds getting ready for the first press and noticed something that after thinking about it makes perfect sense.
My tip mold is different to my tail mold and therefore there is a differnce between "material ski centre" and "actual ski centre". Where material ski centre is the centre of the ski when base material is laid flat, and actual ski centre is the centre between tip and tail when the ski has been finished.
If you used the same mold tip and tail and the tip and tail height were the same then material ski centre would be the same as the actual ski centre, but if there isn't symmetry then the two are different.
The trouble for me is that I based my sidecut waist point and therefore theoretical mounting point on the flat material centre. Actual ski centre will really be a bit more toards the tail than projected meaning the waist of my ski is going to be more centred.
Its only a couple of centimetres different.
I guess the reality is that there is no right or wrong way of determining these things. I just thought I would share this as an example of where my 2 dimensional thinking ended up placing me in the 3D real world.
In actual fact I made my sidecut based on the flat non cambered running length (waist at 65% of running length) not the "material ski centre". So in the end when the ski sits flat on the snow the waist will still be in the same spot of the effective edge as I had intended. It's just that the actual ski centre is differnt relative to where I thought it would be. As you can tell I think I have thoroughly confused myself!
Is "actual ski centre" less important in these days of rockered skis? Is centre of running length more relavent?
Maybe I should just make symmetrical skis and I won't need to worry!
When ski centre isn't ski centre
Moderators: Head Monkey, kelvin, bigKam, skidesmond, chrismp
When ski centre isn't ski centre
Don't wait up, I'm off to kill Summer....
I just drew it all on AUTOCAD and my differnce is only a matter of millimetres not centimetres. I guess what I was interested to see was that I was drawing what I thought were ski centre lines to allign molds and cassette in the press, but what I was actually drawing was just the centre of my cut out materials. In the end it doesn't matter that much as long as the line represents the same thing in all cases. Just academic. Maybe this is why sometimes marked ski centre on commercial skis is so far out?
Don't wait up, I'm off to kill Summer....
Funny. This thinking took me aswell a couple of months to get over. And then I just skipped everything and made my "own" formula. I just put my toe on the middle of the ski. The ski lenght/2. And then I didn't have to think about that anymore...:-)
But thats for my skis. And they "deliver"!
I use SnoCad-X, and it does the job for me.
But I'm a traditionalist and hang out in the piste.
JP
But thats for my skis. And they "deliver"!
I use SnoCad-X, and it does the job for me.
But I'm a traditionalist and hang out in the piste.
JP
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skidesmond
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- Location: Western Mass, USA
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I think you hit on the same dilemma that everyone else has pondered, myself included. I use SnoCadx too, easy to use for basic designing and still allows for customizing of camber setbacks and side cut bias.
I checked a template I made using Snocadx and it always puts the center line evenly between the running length (ie between the contact points of the tip and tail).
You can play around with the shape of the ski with-in the running length with SnodCadx. By changing the side cut bias you can move where you want the narrowest part of the ski forward or backward.
I've used a side cut bias of +55mm and leave the camber set back at 0. I leave the camber setback at 0 because I want the ball of my foot at the height of the camber since that's where most of the pressure and steering of the ski occurs. (* Maybe I should use a camber set back to 55mm also, now that I think about it? *)
When you print the ski template in SnoCadx the center line will still be 1/2 way between the running length. I then make a new line 55 mm behind the center line and I use that as my boot center.
The reason I do this is it seems that most folks are mounting the boot center 55-65mm behind the center of the running length of the ski. So based on that info I moved the narrowest part of the ski, and boot center to the same point of the ski. This places the ball of my foot at the center line of the ski that SnoCadx printed out and also puts the ball of my foot at the highest camber point.
If you play around with SnoCadx and use ridiculous numbers you'll see how it effects the design/shape of the ski. Using 55mm is fairly modest. The width difference of my new boot center and center line as defined by SnoCadx is less than 2 mm.
Maybe the highest camber point, narrowest point and boot center should all be at the exact same point? Either way, these points all fit between the ball of my foot and the boot center.
I'm happy so far with the way the skis have performed.
What do others do?
I checked a template I made using Snocadx and it always puts the center line evenly between the running length (ie between the contact points of the tip and tail).
You can play around with the shape of the ski with-in the running length with SnodCadx. By changing the side cut bias you can move where you want the narrowest part of the ski forward or backward.
I've used a side cut bias of +55mm and leave the camber set back at 0. I leave the camber setback at 0 because I want the ball of my foot at the height of the camber since that's where most of the pressure and steering of the ski occurs. (* Maybe I should use a camber set back to 55mm also, now that I think about it? *)
When you print the ski template in SnoCadx the center line will still be 1/2 way between the running length. I then make a new line 55 mm behind the center line and I use that as my boot center.
The reason I do this is it seems that most folks are mounting the boot center 55-65mm behind the center of the running length of the ski. So based on that info I moved the narrowest part of the ski, and boot center to the same point of the ski. This places the ball of my foot at the center line of the ski that SnoCadx printed out and also puts the ball of my foot at the highest camber point.
If you play around with SnoCadx and use ridiculous numbers you'll see how it effects the design/shape of the ski. Using 55mm is fairly modest. The width difference of my new boot center and center line as defined by SnoCadx is less than 2 mm.
Maybe the highest camber point, narrowest point and boot center should all be at the exact same point? Either way, these points all fit between the ball of my foot and the boot center.
I'm happy so far with the way the skis have performed.
What do others do?
I modeled my 184cm Volkl AC4 dimensions to get this whole ski building project started three years ago. They have the waist of the ski about 50mm aft of the max camber point. Obviously the max camber location is midway between the contact points.
The ski waist (center of turning radii) corresponds to the boot mid-sole location.
I’ve maintained this setback dimension for several ski designs with excellent on-mountain success. My CAD models have datum planes established for the max camber point (my tooling reference line), the two contact points, and the boot mid-sole. The ski press shape and ski plan shape are both generated within a single Solidworks model. Base templates, tip and tail filler templates, and sidewall block core trim templates all fall out of this model. I use tangent splines and arcs to create ski shapes. I used ellipses earlier but they are too constrained. I keep the max tip and tail width locations outside of the contact points to provide a nice long effective turning edge.
One thing I learned early on is that the cured ski perfectly matches the press form so future designs take this into account, there is no “spring back”.
Cheers,
-S
The ski waist (center of turning radii) corresponds to the boot mid-sole location.
I’ve maintained this setback dimension for several ski designs with excellent on-mountain success. My CAD models have datum planes established for the max camber point (my tooling reference line), the two contact points, and the boot mid-sole. The ski press shape and ski plan shape are both generated within a single Solidworks model. Base templates, tip and tail filler templates, and sidewall block core trim templates all fall out of this model. I use tangent splines and arcs to create ski shapes. I used ellipses earlier but they are too constrained. I keep the max tip and tail width locations outside of the contact points to provide a nice long effective turning edge.
One thing I learned early on is that the cured ski perfectly matches the press form so future designs take this into account, there is no “spring back”.
Cheers,
-S
I set my sidecut set back 65mm back but put the center of my camber at the center of the running length.
Boot center almost always ends up at my sidecut setback but ball of foot ends up at center of running length.
So far its worked out pretty good.
YMMV !!
Not sure what would happen if ball of foot and the skinniest (sp?) part of the ski were on the same line.
whoo hoo... 200 posts of, hopefully not, meaningless drivel !!
Thanks for putting up with me!
sam
Boot center almost always ends up at my sidecut setback but ball of foot ends up at center of running length.
So far its worked out pretty good.
YMMV !!
Not sure what would happen if ball of foot and the skinniest (sp?) part of the ski were on the same line.
whoo hoo... 200 posts of, hopefully not, meaningless drivel !!
Thanks for putting up with me!
sam
You don't even have a legit signature, nothing to reveal who you are and what you do...
Best of luck to you. (uneva)
Best of luck to you. (uneva)
No worries.
I will see how my designs turn out. Narrowest point is a bit back of centre will mount so the ball of the foot is about on centre and boot centre is at the narrowest point. Good to see I am on the same track as everyone else, therefore on the right track!
Well done sammer. Fernie would be a great testing ground. I was there season 04/05. Worst season in a while apparently. Lots of rain!
I will see how my designs turn out. Narrowest point is a bit back of centre will mount so the ball of the foot is about on centre and boot centre is at the narrowest point. Good to see I am on the same track as everyone else, therefore on the right track!
Well done sammer. Fernie would be a great testing ground. I was there season 04/05. Worst season in a while apparently. Lots of rain!
Don't wait up, I'm off to kill Summer....
I read somewhere in the past that the waist of the ski should be around 55% of the running surface length. So if a person wanted to put the ball of their foot on the mid running length and the center of their boot on the waist, I would imagine that it would be pretty easy to measure that distance on the average foot and make that your dimension. For my
boot, it is about 2.5-2.75 inches or 63.5m-69.85mm.
As far as moving your mount 1 or 2 cm, it makes a huge difference in the way the ski feels. I have a Marker Schizo that can be moved about 1-1/2 inches in any increment you want of the range and it is amazing how much different the skis perform.
boot, it is about 2.5-2.75 inches or 63.5m-69.85mm.
As far as moving your mount 1 or 2 cm, it makes a huge difference in the way the ski feels. I have a Marker Schizo that can be moved about 1-1/2 inches in any increment you want of the range and it is amazing how much different the skis perform.