Author Topic: Bow Design  (Read 4709 times)

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Offline DC

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Bow Design
« on: July 29, 2019, 02:35:04 pm »
Something I've often wondered about is bow "design". Merriam Webster says " to devise for a specific function or end". I don't think I've ever consciously designed a bow, I pick up a piece of wood and make it bend as evenly as I can and hope it's got good cast. I don't sit down with a pencil and paper before hand and draw a picture. On another thread about sinew most people said that a bow has to be designed around sinew. I've heard that before but I don't think I've seen an explanation of what a "sinew design" looks like or the thought that goes into it. In general a bow should fling an arrow as far as possible so really they are all designed for the same thing. So in your experience what is involved in designing a bow?

Offline Pat B

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Re: Bow Design
« Reply #1 on: July 29, 2019, 02:54:56 pm »
My thoughts are that depending on the wood used the bow design should take advantage of the tension and compression strengths for best results.  As far as a sinew backed bow the bow should be short enough to get the most the sinew has to offer at a given draw length so a bow with a 2/1 bow length to draw length or less to get the optimum results from the sinew.
Make the most of all that comes and the least of all that goes!    Pat Brennan  Brevard, NC

Offline DC

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Re: Bow Design
« Reply #2 on: July 29, 2019, 03:00:55 pm »
My thoughts are that depending on the wood used the bow design should take advantage of the tension and compression strengths for best results.

So this would be the red Oak bow should be wider and/or longer than a yew bow of the same DW/DL thing?

Offline Ringeck85

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Re: Bow Design
« Reply #3 on: July 29, 2019, 03:07:03 pm »
What each kind of bow wood or composite materials are best for (tension, compression, durability, etc etc.) and designing a bow that maximizes their best qualities and minimizes their downsides.

Great example is hickory (add lots of other white woods to this like hard maple, ash, etc. etc.).  Forgiving material and you can make many kinds of bow designs with it.  But making it flatter/rectangular in cross section (as in a flatbow with or without a stiff handle/riser) to take advantage of its strength in tension and to minimize its less than exemplary compressive strength.  Otherwise, if you try to make it into say, a heavy weight longbow/warbow with that kind of deep oval cross section, there's a high chance it will either take a ton of string follow/set or develop compression fractures/chrysals/frets (are those actually interchangeably the same thing or is there a distinction? would love to clarify!)

Osage and yew are better balanced between tension and compression, but have their challenges as well. Yew is well balanced, and does either an oval section or a flatbow design very well.  Quality varies considerablyfrom stave to stave, and it requires a Lot of careful handling of knots, and since the wood is a little softer it's probably easy to take too much wood off by accident (please chime in people who have experience working with yew!!).  Osage is less forgiving on the back than hickory, so you need to chase a ring Or back it so it won't fail in tension.  But it's much better with compression so it can handle a fair variety of bow designs.  It tends to be --from what I think I understand?-- to be most efficient at lower draw weights as some sort of a flatbow type of design though, as it was used historically and with traditional modern flatbows as well.

Context is important to consider in "design" as well.  Are you trying to get your stick of wood to cast an arrow as quickly and efficiently as possible as far as fps and all that jazz? (I'm thinking more modern riser-shelf flatbows here?)  Then you need to pick the best possible bow wood (or woods or composite materials if you're making a laminate) and choose a design that optimizes the bow's performance.

Are you trying to make an extremely accurate bow?  Modern olympic recurves are designed, with modern materials, to shoot light arrows extremely accurately in extremely competitive contests to score points.  Not saying they are better than traditional (that would be like blasphemy to say on this site!  ;D ) but they are definitely designed for a different context.

Or are you going for a bow that say, is a little easier to make in less time, and is durable for what you need it, even if it casts slower?  Let's say a Cherokee style or a Sudbury designed hunting weight (45-60 lbs. or so) flatbow? Depending on how the bowyer makes it, Some Set/string follow, wider tips, slower cast, etc. is fine as the bow is designed primarily for durability in a moist hunting environment (so self bows would be both easier and more practical), ease of use, and definitely ease of manufacture (stone/bone/copper tools pre-Columbian exchange).

Those are my thoughts anyway.  Anyone feel free to chime in, and any feedback to expand or correct what I've said is welcome constructively.
"It is how we choose what we do, and how we approach it, that determines whether the sum of our days adds up to a formless blur, or to something resembling a work of art."
-Mihaly Csikszentmihalyi

(Ren', in Wytheville, VA)

Offline DC

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Re: Bow Design
« Reply #4 on: July 29, 2019, 03:25:03 pm »
Maybe where I'm getting confused is that people don't differentiate between design=plan and design=type so when someone says, "that's the wrong design" I 'm not sure if they mean I have my dimensions wrong or I should have built a Cherokee rather than an RD.

Offline Pat B

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Re: Bow Design
« Reply #5 on: July 29, 2019, 03:28:37 pm »
DC, yes.
 Some woods are tension strong but weaker in compression so designing your bow with a trapped cross section can equalize these properties so the bow is less stressed. A trapped cross section(trapezoidal) can go either way, either strengthening the back or belly, depending on the wood's qualities. Once you are familiar with the different qualities of different woods you just know which way to go without having to design a bow on paper.
Make the most of all that comes and the least of all that goes!    Pat Brennan  Brevard, NC

Offline Ringeck85

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Re: Bow Design
« Reply #6 on: July 29, 2019, 03:39:24 pm »
Personally, after my fourth stupid breakage in a row (I still suck at tillering haha!), I find that if I did not carefully lay out the bow's profile well enough in advance and take my time with that, I make stupid mistakes that make tillering the bow much harder and more finicky later.  So, starting out, draw those profiles would be my advice from my Very limited experience!!  And be paitent, take your time, and do Not overdraw that bow! X_X  (I am learning this the hard way, attempting to make bows out of sourwood lol)
"It is how we choose what we do, and how we approach it, that determines whether the sum of our days adds up to a formless blur, or to something resembling a work of art."
-Mihaly Csikszentmihalyi

(Ren', in Wytheville, VA)

Offline DC

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Re: Bow Design
« Reply #7 on: July 29, 2019, 03:43:30 pm »
Front or side profile?

Offline Ringeck85

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Re: Bow Design
« Reply #8 on: July 29, 2019, 04:16:16 pm »
Front.  But side profile helps especially on board staves where you have a clean flat surface to draw lines on.  On split staves it can be trickier to do that (I need to get some caliphers to measure thickness for that, I don't trust my eyes)
"It is how we choose what we do, and how we approach it, that determines whether the sum of our days adds up to a formless blur, or to something resembling a work of art."
-Mihaly Csikszentmihalyi

(Ren', in Wytheville, VA)

Offline Woodely

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Re: Bow Design
« Reply #9 on: July 29, 2019, 05:43:49 pm »
I'll sit down and design a takedown somewhat ,   at least something to give me an idea where to start and end with some dimensions.   I always have other bows hanging on the rack for reference,   So this is my experience involved in designing a bow?
"Doing bad work is an exercise in futility, but honestly making mistakes is trying your best."

Offline Stick Bender

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Re: Bow Design
« Reply #10 on: July 29, 2019, 07:02:16 pm »
I think when I design a bow I always start with a idea what I'm looking for ,do I want a bow that shoots light arrows fast or a bow that shoots heavy arrows fast do I want a long length bow or a shorter bow Ect the choices are endless then I choose a design and materials that will work for it and make one then if it's not right change it and make another & another & another some how I never make the perfect design & have to make another  :D
If you fear failure you will never Try !

Offline DC

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Re: Bow Design
« Reply #11 on: July 29, 2019, 07:35:58 pm »
,do I want a bow that shoots light arrows fast or a bow that shoots heavy arrows fast
What would you do differently if you don't mind? I've had trouble sorting this part out.

Offline Stick Bender

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Re: Bow Design
« Reply #12 on: July 29, 2019, 07:45:49 pm »
That's a hard question to answer In a post but in short if I want a bow to shoot light arrows I would use the shortest limbs in a design that won't stack at my draw with out over stressing the material & for a heavy arrow bows longer limbs generally I have found a good performing short bow will work well in a longer version for heavy arrows but a bow designed around heavy arrows doesn't always work shorter mainly do to stack !
If you fear failure you will never Try !

Offline Stick Bender

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Re: Bow Design
« Reply #13 on: July 30, 2019, 07:38:08 am »
When I design a bow I just use a simple formula I choose a design that gives me the best posible early draw weight with the best string angle at FD really pretty simple , just getting there takes building a lot of bows is the problem but I have also found some of the fastest bows I have built are really not good hunting bows not user freindly or accurate so that adds another dimension to design fast, accurate & user friendly  :D
If you fear failure you will never Try !

Offline Dances with squirrels

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Re: Bow Design
« Reply #14 on: July 30, 2019, 08:05:08 am »
Yep, much to consider, if ya want. There are bow qualities that factor into design that may be found just as, or more important than speed. Sometimes I feel as much choreographer as woodworker.
Straight wood may make a better bow, but crooked wood makes a better bowyer