Shape of the sidecut

[István]

Guys,

Technical question: what is the difference of an elliptical and a parabolic sidecut.

Pls someone explain me also the geometrical consequences of it, i.e. what is the difference when a parabolic/elliptical sidecut meets a flat surface.

Also would like to know the impacts of the sidecut shape on the performance/riding of the board.


Cheers.

István

[István]

Did I ask something too simple or too complicated?? No responses so far....

[Simon]

too difficult!

isn't there a progressive sidecut too?

Elliptical and parabolic sidecut describes how the radius of the sidecut changes over the lenght of the board.

If I remember right, swoard uses a circular sidecut, so the radius is always the same.
Parabolic sidecut: bigger radius at tip/tail than at the middle of the board following a parabolic curve. The radius must not be the same at tip and tail, I think thats called progressiv or declining sidecut.
Elliptical sidecut: I think that's almost the same, bigger at tip/tail but with a slightly different allocation.

please correct me, if I'm wrong and how changes the behavior of the board?

Now I want to know it exactly, come on!

Simon

[Simon]

Is it possible to ride a board with a small sidecut radius at tip/tail and a big one at the centre of the board? It would also be an elliptical curve, simply rotate the ellipse at 90°.

[Simon]

I played with some formulas of ellipse, circle, parabola and plotted a few curves to visualize this topic. Have a look at the plot:

[tufty]

I played with some formulas of ellipse, circle, parabola and plotted a few curves to visualize this topic. Have a look at the plot:

Is that the curves themselves, or the curve obtained when applying a curve to a curved board in order to make it 'sit' on a flat surface at a given angle?

To visualise the curves themselves, you have to start thinking in terms of conic sections, which is what they all are - a good place to go is wolfram's site, here.

Once you start cutting them into planes, curving those and tilting them to try and work out contact curves, things get really hairy really fast. I could probably work out some math for them, but my brain's fried after 14 hours of work today.

As for what difference they make when applied to a particular board sidecut, and what the actual technical diference is between two sidecut types on otherwise identical boards, my personal answer would be "stop asking questions that make my brain bleed". I would imagine the most important differences would be the shape and radius of "perfect" carve for a given board inclination, the way that that curve changes with relation to inclination, and where the points of maximum pressure are for a given inclination. and other stuff like that.

Simon

[Simon]

That are just the curves themselves, but fitted to the same middle and end points. The radius is much too tight, otherwise you really can't see any difference.

My question is how this curves are applied to the board and how the board reacts.

Simon

(I don't want to fry other brains)

[Chris Houghton]

This is one of the "secrets" of board manufacture, I think we cannot analyze the effect of different types of sidecuts because they all appear on different boards. My favourite is the sidecut that allows the tail to follow the nose exactly, making one thin line in the snow. This makes a very smooth quiet ride. But others work well (Virus for example) where the radius allows the board to be ready for any radius of turn.

[skywalker]

So here comes some theory which is only my little thoughs:

The goal, you want to achieve when building a carving board is a circle of the edge in the snow in a carved turn. This curve is a function of sidecut and angle between board and surface, which first of all depends on torsional behaviour of the board. Nevertheles I will not care about torsion, because this does not change the principle of sidecut layout, only the numbers

So what I did in some free minutes was to create a dull and ugly snowboard-dummy. I defined a sidecut depth of 22mm (like an FP for example), but did not cut a radius or anything like that. Then I projected the characteristic points of this sidcut to a inclined plane.



Based on the resulting point, I created a resulting circle



This circle was the base for an extrude...



...and the result is a parabolic sidecut


Please note, that this is only theory. But IMHO this makes hyperbolic sidecut look strange in my eyes. BTW: The difference between an circle and a parabola, which leads to aperfect projected circle under 45° is less than 0.02mm, so CATIA V5 is not able to calculate it

Just 2 ct...

skywalker

[István]

Skywalker,

I think I got lost in your argumentation. Did you arrive to the conclusion that boards should have parabolic sidecuts? Or I completely misunderstood....

Viruses have parabolic sidecuts, is that correct?

Best,

István

[skywalker]

Hello István.

Skywalker,

I think I got lost in your argumentation.

sorry about that. I thought, it was a good one;) Just stay focussed on the goal of a perfectly round shape of a bent board on the snow.

Did you arrive to the conclusion that boards should have parabolic sidecuts?

I would never tell a board-builder how to build his boards. Maybe I come to the comclusion, that in theory a parabolic sidecut might work better...

Edit: To use the words as defined before I should call that "elliptical along"

Viruses have parabolic sidecuts, is that correct?

I don't know. They just take about "built out of several radii", no idea, in which way. There is even a combination possible like big radius at the beginning, smaller, even smaller, wider, little wider, little smaller, smaller, wider, wider. No idea, if this would be of any use, but as I mentioned before: The differences are so small, that a board would work anyways

skywalker

[kelvin o]

Some thoughts...

The precision of the sidecut would only show up if the piste were perfectly flat and perfectly hard (an ice rink would be an example). Since snow, even relatively hard snow, is deformable along the plane of the carve the minute difference between the shapes would be lost. The depth of the trench would simply swallow up the differences. The approximate radius of the sidecut or the effective depth of the sidecut is going to make a much bigger difference. Also if the shape was going to have any effect on the board performance the board flex would have to be tuned to perform collaboratively with the sidecut shape and the rider would have to be perfectly balanced on the board to get the board to get full edge contact...

It just seems the differences between the sidecut shapes are engineering exercises that don't really have much affect in the real world but give the marketing department something to crow about.

my 2 cents... (or whatever a 1/100 of a Euro is called)

[István]

Surprisingly its called EuroCent...

[kjl]

If the shape was going to have any effect on the board performance the board flex would have to be tuned to perform collaboratively with the sidecut shape and the rider would have to be perfectly balanced on the board to get the board to get full edge contact...

I don't know about that. The flex+camber on the board provides force along the entire board - it seems like at the minimum all of the edge in the nose and in the tail will contact the snow as long as you are heavy enough to push the edge under the bindings to the snow. Perhaps the edge between the bindings does not, though I expect it does as well.

My intuition tells me you may be right w/r/t to the shape of the sidecut not affecting the contact shape very much... if it really mattered it should be obvious (one kind of sidecut would best approximate a circular arc when bent and contacting the snow, and that would be much superior to all the other shapes), but it's not really that obvious from board to board, in my opinion.

I haven't done any math, but I would guess that neither circular, elliptical, or parabolic sidecuts actually contact the snow plane in a circular arc, nor that a shape could be made that would contact the snow plane in a circular arc at different edge angles (e.g. at both 30 and 70 degrees of inclination).

It would be interesting to choose a "most important" edge angle, like, say, for EC somewhere between 70 and 80 degrees, design a perfectly circular arc, and reverse engineer the exact sidecut shape and see what you get.

[kjl]

Oh, hah - I didn't even see above Skywalker already did the math.

Although to be over precise you can't actually project like that, as the board doesn't project, but bends (so from an overhead point of view it shortens as it flexes). Probably a negligible amount, but maybe not when it becomes very, very flexed at high edge angle :P