Recurve design project

[Pago]

So I'm tackling my first design project.  This is very raw but actually represents a chunk of time learning how to do things.  So spare some time to kick this around with me if you have it to spare and let's see where this eventually ends up.  No holds barred any input welcome. It's modeled as osage in supertiller. Sketchup 2D uses a 20 inch riser (I like the old groves bows) but the limbs are too long I think.  We will see where it goes.


 

 

 

[BenBow]

Pago I love playing with supetiller. My first reaction is your limb is ony bending at the fade which means the rest of the limb isn't contributing anything except a leaver effect. You might try adding some taper to your limb to get more of it bending. Also be sure to add the thickness of your riser so it will show up as non bending. This will move the working portion out onto the mid limb. It maybe you only added the limb portion to supertiller. If so you have 60" of limb plus the length of your riser which will be one very long bow. Just suggest you include the riser and limb to see how they interact and it will give you a better indication of the actual length of the bow.  
Have fun!!!

[Pago]

Thanks Ben. I did as you suggested and shortened up the limb.  It needs more work but here is some more to look at.

 

 

[BenBow]

Pago what do you think of the desigh so far?

[Pago]

Oh boy feels like a loaded question.  There is more that I don't know than I do know so I worry about my inexperience getting the better of me.  However, from my perspective I am pretty tickled with the projected performance and the way the limb is unfolding. String angle looks good.  Draw force curve looks good to me.  The weight jumps up right at the first of the draw and then settles down to right at 2 lbs. per inch through the rest of the draw.  I was initially shooting for something with deeper hooks but I have been doing a lot of reading and experimenting and this is where it has led me. To me it almost looks like a cross between a long bow and a recurve.  As it currently stands I could build this either one piece or three piece the limb pads on the front are at 20 degrees which is recurve territory.  Time to do some more studying and thinking to decide what the next step is I am thinking. I'm glad to be able to kick it around with another boyer, thanks.

[BenBow]

When you decide on your design supertiller can print out a full size template for your form. Takes a little playing with it but it will print out multiple 8x11 sheets that can be taped together.

[Pago]

Thanks, although you didn't give the critical analysis I'd hoped you would I am grateful for your input. I started using google sketchup about 3 years ago and while I'm not a pro at it I get bye.  The rendering above is a 2D export from sketchup and is true to scale in the program. I used the coordinates from supertiller to construct the limb in sketchup.  I will do a full 3D render of the bow both raw and finished before I build and print the form with all critical measurements included at a print shop.  I will start out with a full set of blueprints.

[BenBow]

Pago a couple of things you haven't mentioned are the lamination stack layup and the width taper. Do you have any tapered lamination? Will the width taper evenly to the tip or stay parallel then taper to the tip like a recurve bow? All of this will influence the bending rate of your limb. As I look closely at the last group the limb profile looks wavy rather than an even bend is that what you're going for? I'll ask more critical questions to help you analyze and decide on what you're after.    
Oh and one other thing, do you have a wedge fivured in. Right now it appears to be bending right off the riser. On a one piece you have to figure length of the fadouts into the thicker portion of the riser and have that thickness entered in supertiller to get a truer sense of how the limb will bend.

[Pago]

That's more like it lol. I can't get to all that yet but here is something to look at.  My first rendering of a bow in google sketchup.

 

[BenBow]

Having fun now      Here is a picture of how I use sketchup to enter data in supertiller. By the way you can import pictures into sketchup and use them as a pattern which is what I did with this. I create a baseline and put in the dimensions every 2". Then I enter that data into supertiller and see what happens.
   

[Pago]

That's cool, I use pictures in sketchup a lot.  I prototype just about everything I build in sketchup and overtime I get more sophisticated.
This bow is definitely looking like a recurve with longbow limbs but that might not be a bad thing. I will build it as a one piece first and use that to figure out the wedge to build my first take down from there. Currently it tapers from 2" to .33" at the tips, the thickness is kind of meaningless right now but the taper is .004 per inch.