Curvature recurve

[ocramvb]

Hi everyone, I'm new here  

For the last few months I'm researching bows because I want to start making my own traditional bow. I've learned a lot on materials and woodworking but there are two things I can't figure out:

1. How should you determine the curvature of the limbs? What is the radius of the tip?
2. Can you predefine the brace height of the bow while designing it? Or is that determined after the bow is 'finished'

Hope you can help me to answer these questions   . Thank you!

[AJMag]

Can you be more specific on what you want to build..... be it a glass laminated bow or a selfbow, etc.

[Swissbow]

I would recommend to use a proven design for the first recurve, because a lot of variables come into play when designing a recurve. Otherwise you eventually might need a few attempts to get a decent shooting bow.

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Andy

[talkingcabbage]

I agree with Andy. Do a few with a proven design first to get the process and some basic skills down, then start tinkering with different limb profiles, shapes, curves, etc. You can check with Kenny M here or on Bingham's website.

[ocramvb]

Thank you all for the responses!  

Ofcourse, a proven design should be the first thing I make. But, as an academic, I'm interested in the why of things. The design is proven, but why is it proven? I can't find any reasoning.

For me it would be interesting to hear why the curvatures of the limbs are what are, and why the curvatures of the tips are what they are.

The bow I want to make is a recurve bow. And I'm wondering what the influence is of the curvature of the limbs, the curvature of the tips (more agressive, or not) and how I could design for a low (or high) brace height.  

[dfrois]

My best recommendation is to read the Performance chapters of the TBB series of books. Ther you will find what is the influence of each of the design parameters on a bow, be it longbow, D/R, or recurve. The authors are VERY knowledgeable, have a scientific mind (i.e, they don't pay attention to established prejudices, but instead test and measure/verify each parameters influence) and really bring some of this stuff out in the open. The fact that it is written with wooden bows in mind changes nothing to the main parameters, since most of it is geometric or stress-related. The materials only come into play later, when they must be selected for actual building.

There are probably other sources, but this is the best that I know of.

Good luck.

DF

[LittleBen]

I agree with dfrois. Read the TBB series. This will give you some understanding of the principles you are talking about.

[carpin'mark]

A proven design is just that, a proven design because it works well. It's simply to give a novice a higher chance of success. It's not only the curvature of the limb that determines how a bow behaves, glass thickness, what combination of parallel and taper thickness can also have an effect on where and when the limb flexes and compresses.
While I agree with you that most everything can be put to a mathematical formula, you might find bow building has a certain intangible quality, at least I hope you do - because that's what makes it so interesting.

[LittleBen]

Yeah again I second what these guys have said, stick with a proven design.

Frankly unless you're an engineer and capable of complex calculation, and familiar with mechanics (statics and dynamics), the likelyhood of improving a well established design is low, especially on your first go around.

FWIW, if you're interested in how changes in limb shape will affect draw force curve, etc. check out supertiller. It's a macro enabled excel spreadsheet that allows you to test different designs.

This is a supertiller build along to get you started
  http://www.buildyourownbow.com/build-alongs/supertiller/

[John Scifres]

There are two basic types of recurves: working and  static.

Working recurves uncurl as the bow is drawn.  Static do not.

Working recurves add cast through their work.

Static recurves provide leverage and make a bow easier to draw a longer distance by this leverage.

Most wooden recurves are statics.  Most modern fiberglass or carbon recurves are working recurves; although several makers also make statics.

The question on designing for brace height is a little odd.  What are you trying to accomplish with designing for a specific brace height?

[ocramvb]

Thank you all again for the comments!

I am going to order TTB series.

About the brace height:, I want to know or estimate on forehand what the 'sweet spot' of the bow would be.

Will the curvature of the limbs be of an influence to that?

[dfrois]

Off the top of my mind, limb profile, riser size, limb pocket angle, amount of deflex, amount of reflex, string length, materials used...these are only a FEW of the many variables that affect the brace height and, therefor, the elusive "sweet spot" that you are trying to estimate. I don't think you will suceed. Not until you have a lot of experience with similar designs, varying only one or two parameters between bows. And even then, you would have to spend more time measuring them than shooting...hopefully, after you build a couple, you will be having so much fun with them that you will not want to waste time measuring instead of shooting. It is a hobby, right?

DF

[MoeM]

Won`t be a thing with FEM or even the supertiller "app" for excel...