Progressive SC - Tri-radial geometry

Carvejunky · Post by **Carvejunky** » Sun Feb 08, 2009 4:53 pm

Here is a question for you guy's that do the progressive sidecut or bi-radial and tri-radial shapes. One of my favorite boards for the Ice Coast is a Madd. It had a tri-radial design, not sure of the numbers for the 170 but the 158 had a 7/11/9 M ( so I've heard ). I am trying to picture the actual geometry. Are the Radii evenly distributed along the SC, or in the case of a snowboard would you match the radii to the setback of the binding inserts. Geometrically you could make them 30%@7M 40%@11M 30%@9M, or 33% all.
Just wondering what the norm would be...

Carvejunky

doughboyshredder · Post by **doughboyshredder** » Sun Feb 08, 2009 6:18 pm

Design theories vary. I personally like a centered sidecut on a snowboard regardless of the stance setback. Some boards however have the sidecut shifted the same as the stance.

Currently I am building my boards with a larger radius sidecut under foot for letting it run. 25% 8.5m, 50% 9m, 25% 8.5. This is on a 166.

Carvejunky · Post by **Carvejunky** » Mon Feb 09, 2009 10:09 am

Thanks for the reply...

I am looking at running the large SC the length of the inserts and letting the others fall were they may. If the sidecut is shifted back it creates taper in the board so that is something I will be looking at doing in the future. As the geometry stands it will create a very slight taper but I myself like a centered board. Easier to ride and seems quicker edge to edge for me.

Thanks again

doughboyshredder · Post by **doughboyshredder** » Mon Feb 09, 2009 11:07 am

Carvejunky wrote:Thanks for the reply...

I am looking at running the large SC the length of the inserts and letting the others fall were they may. If the sidecut is shifted back it creates taper in the board so that is something I will be looking at doing in the future. As the geometry stands it will create a very slight taper but I myself like a centered board. Easier to ride and seems quicker edge to edge for me.

Thanks again

You're welcome.

Taper is created by making the tail contact point narrower than the tip. Where the center of the sidecut is has nothing to do with taper.

For example a twin tip shape can have the center of the sidecut at the center of the board. If you shift the center of the sidecut while leaving the shape of the board the same you end up with a smaller (tighter) radius towards the tail and a bigger (straighter) radius towards the tip, without affecting the taper (or lack thereof).

Conversely if you leave the sidecut radius centered, but taper the tail you will have a bigger radius towards the tail. This is why on most tapered boards the sidecut is also shifted towards the tail.

Carvejunky · Post by **Carvejunky** » Mon Feb 09, 2009 1:09 pm

Where the center of the sidecut is has nothing to do with taper.

Sure it does.... My wife always says I don't explain things properly. They say a pic is worth a thousand words so here's my thousand... Hope this makes sense. When I realized this it allowed me to make my parts modular so I can build custom boards from templates.

In this image both boards are the sane, 14.5M sidecut. What I did was move the sidecut 1.477" linearly back, the center moved back 1.477" . it creates 4mm of taper. Kind of neat, huh?

Actually were both saying the same thing in a different way, LOL

doughboyshredder · Post by **doughboyshredder** » Mon Feb 09, 2009 1:51 pm

You are wrong.

Taper refers to one thing and one thing only. Whether the tail is narrower than the tip. Sidecuts have nothing to do with it.

doughboyshredder · Post by **doughboyshredder** » Mon Feb 09, 2009 2:13 pm

If you notice the second board while not a taper does have the center of the sidecut shifted 20 cm back resulting in a much tighter radius in the tail section of the board.

Carvejunky · Post by **Carvejunky** » Mon Feb 09, 2009 2:16 pm

Okay.... I guess geometry lies.

I am creating taper in my boards by adjusting the Center of the sidecut radius linearly to the rear by 1.477" as you can clearly see in the drawing. I do this to get away from the angular measurements which are so small. When I do this it creates a wider nose and a narrower tail. I believe that is the definition of TAPER. Please don't tell me I am wrong as I have designed Machined parts using this same concept.

Before you say I am wrong I think you owe it to yourself to try reproducing the geometry. I have 12 cores built using this concept with 0mm to 6mm of taper using radial sidecuts. I am not discussing what the definition of taper is both you and I know what that is! I am trying to show you an alternate way of making the same thing. If I am wrong how did I make this drawing? The dimensions are there, you can reproduce it if you like, but you should not say the geometry is wrong until you do.

However... I do appreciate your response to my original query...

P.S. You can't draw the geometry in snocad it works differently...

Per Dan Graf

Change the "sidecut bias" setting on the rails menu - that will offset the focus of the sidecut back, and tighten the radius towards the tail

dan

You are working with a focus and that is not the same geometrically as what I am saying. If you look at your image you should notice that it is not a single defined radius. Even Dan eludes to the fact that there are more than one radius by saying it tightens the radius towards the tail. I am talking about a pure radial arc. Are your rails defined as Quadratic or 7 point spline? That is not the same as a radial sidecut. When you work with a focus point that is not the center of a circle. Am I right or wrong?

doughboyshredder · Post by **doughboyshredder** » Mon Feb 09, 2009 3:53 pm

Sorry, I misread your post, I thought you said that shifting the center of the sidecut radius creates a taper. You actually said that shifting the sidecut linearly would create a taper. I said that shifting the center of the sidecut radius without changing the width of the contact point on the tail creates a board with different sidecut radius.

So we are both right, as is obvious by our drawings

Really, we are talking about different things.

As I showed in my drawings the placement of the sidecut has nothing to do with whether a board has a taper.

And actually you can do it snocad you just have to manually change the dimensions of the tail.

Carvejunky · Post by **Carvejunky** » Mon Feb 09, 2009 5:05 pm

If you shift the sidecut as I suggest the center point also moves linearly as the arc does. It would have to... Because you are using SnoCAD, your curve shape is changing mine is not. I don't want to change the shape of the curve I just want to induce taper. When you move the arc, and the center along with it the nose and tail width also change. I think this drawing will illustrate much better.

[/img]

doughboyshredder · Post by **doughboyshredder** » Mon Feb 09, 2009 5:18 pm

Uhh, yeah that's what I already said.

And, that is just a limitation of snocad, like I said easily taken care of by manipulating the tail width manually.

Your last post seems pretty condescending and rude. I'm not fcuking stupid.

In case you haven't figured it out, you are shifting the entire arc maintaining the same radii which obviously moves the centerpoint and creates taper. I am shifting the center point only which redefines the radii and does not create a taper.

Like my first post said, design theories vary. Like my last post said we're actually both correct in our statements. My argument was simply that shifting the center point of the radius (without shifting the entire radius) does not create taper. Right?

Carvejunky · Post by **Carvejunky** » Mon Feb 09, 2009 6:08 pm

Dude,

I thought we were having a discussion about geometry not an argument. I was merely try to show you how I derive my geometry since you said I was wrong. I was actually excited we were having this discussion, I thought I could show someone my ideas for the geometry.

If you shift the sidecut as I suggest the center point also moves linearly as the arc does. It would have to... Because you are using SnoCAD, your curve shape is changing mine is not. I don't want to change the shape of the curve I just want to induce taper. When you move the arc, and the center along with it the nose and tail width also change. I think this drawing will illustrate much better.

I really don't understand the f* stupid remark? I was just trying to show you how I am designing my core geometry. I thought if I could show the difference between SnoCAD and my CAD drawings you could understand my geometry better. I really don't understand how I was condescending or rude.

In case you haven't figured it out, you are shifting the entire arc maintaining the same radii which obviously moves the centerpoint and creates taper

Is this rude, or condescending? I believe I said this before you said I was wrong...

In this image both boards are the sane, 14.5M sidecut. What I did was move the sidecut 1.477" linearly back, the center moved back 1.477" . it creates 4mm of taper. Kind of neat, huh?

doughboyshredder · Post by **doughboyshredder** » Mon Feb 09, 2009 6:22 pm

allright, my bad.

Been a rough monday, sorry I took your posts wrong.

Anyway, back on subject. How are you determining how much to shift the sidecut? Are you shifting it just as much as you need to get the taper you want, or is there a different idea going in to it.

Your core drawings look great btw.

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