# The "Six Circles" Shooter Design by Jörg Sprave



## JoergS

I have been making this style a lot lately, it simply works great and looks good, too.

I realized the beauty lies in the simple radius combination. So I limited the design down to those.

All I needed to create this wonderfully symmetrical design is six circles. Of course this should be sawed out of multiplex or other high quality plywood, 15 to 22 mm, and then some scales (palm swell) should be added, from any kind of material.

Fork height is adjustable to one's needs.

Here you see both the blueprints with the radius's, and the cutout.


















Here is the pdf file.

View attachment SixCircles PDF.pdf


Will be making a nice frame soon!

Good luck making your own.

Jörg


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## shot in the foot

I done one nearly the same as that last year sold it on a carboot, just a touch samer the one i made, jeff


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## e~shot

Thanks Jörg. is scale in CM ?


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## JoergS

Sure... would be a monster in inches, right?


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## e~shot

JoergS said:


> Sure... would be a monster in inches, right?












OK let me give a try to make a PDF of it


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## jskeen

That's bloody brilliant! Beautiful because of it's simplicity, not in spite of it. Did you pick that ratio of 2.5x5.5x12 by trial and error, or design? I almost immediately thought of the "Golden Mean" or "Divine Proportion" of 1.61803 to 1, but I can't seem to make it fit your design.

12 to 5.5 = 2.18 to 1
5.5 to 2.5 = 2.20 to 1 
12 to 2.5 = 4.80 to 1

2.20 to 1 is the standard ratio of 70mm film, and is a formulaic constant used to calculate signal loss in radio frequency transmitters and hysteresis loss in transformers for high voltage power transmissions. Hmmmmm, makes you wonder.

Sorry, had a brief attack of engineers disease. If Tex reads this, I hope he don't catch it, as it's very contagious.

James


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## jskeen

sorry, double post


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## JoergS

No such factor, just trial and error until it all made sense.


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## Dayhiker

jskeen said:


> That's bloody brilliant! Beautiful because of it's simplicity, not in spite of it. Did you pick that ratio of 2.5x5.5x12 by trial and error, or design? I almost immediately thought of the "Golden Mean" or "Divine Proportion" of 1.61803 to 1, but I can't seem to make it fit your design.
> 
> 12 to 5.5 = 2.18 to 1
> 5.5 to 2.5 = 2.20 to 1
> 12 to 2.5 = 4.80 to 1
> 
> 2.20 to 1 is the standard ratio of 70mm film, and is a formulaic constant used to calculate signal loss in radio frequency transmitters and hysteresis loss in transformers for high voltage power transmissions. Hmmmmm, makes you wonder.
> 
> Sorry, had a brief attack of engineers disease. If Tex reads this, I hope he don't catch it, as it's very contagious.
> 
> James


Skeen, I'm no engineer, but I've been trying to work the Golden Ratio into my designs since I started making slingshots. I just know it's gotta fit in there somewhere.


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## Ted

Thanks for sharing!


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## NaturalFork

Great design. I have been shooting the Cougar a lot lately. I think the cougar is your best design ... but that is just personal preference.


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## shawnr5

Looks great, but I think that your fork outside radius should be 6cm, not 5.5. I'm going to have to give this a go. Thanks for sharing with us.


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## JoergS

shawnr5 said:


> I think that your fork outside radius should be 6cm, not 5.5.


True - my bad. Yes, 6 cm.

Jörg


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## shawnr5

JoergS said:


> I think that your fork outside radius should be 6cm, not 5.5.


True - my bad. Yes, 6 cm.

Jörg
[/quote]

No worries. I'm going to get out the compass when I get home tonight, regardless. When I started the Angry Birds slingshot, I made myself a compass that will spin arcs from 6 inches to 28 inches radius, in 1/2 inch increments. This design may require breaking it out again. How would you band it if it were scaled up 3x?

Shawn


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## jskeen

I finally got my cheap knockoff..... um er.... tribute design? Whatever it is, I started with just the single value of the diameter of the forks, and calculated the rest using the ratio of 1.61803399 to 1 after much careful drawing and figuring, the final design I came out with is less than one inch different from the original in any dimension. Pretty interesting how closely experience and testing matched a mathematical formula that was used to design the Parthenon, among other things.


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