Primitive Archer
Main Discussion Area => Bows => Topic started by: Oldvol on February 08, 2022, 12:40:55 pm
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Are there any guidelines on choosing bow width? Is the length or design of the bow a deciding factor? Should it always be as wide as possible? Does extra width cause problems? I have a tendency to make bows at least 2” wide if possible (only made 2). It occurred to me that making a bow wider than necessary might not be a good idea.
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Are there any guidelines on choosing bow width? Is the length or design of the bow a deciding factor? Should it always be as wide as possible? Does extra width cause problems? I have a tendency to make bows at least 2” wide if possible (only made 2). It occurred to me that making a bow wider than necessary might not be a good idea.
I would say a lot of it is based on experience as to what a particular type of wood will take in terms of stress/strain. Bow length, bow design, any reflex/deflex, draw length and draw weight all affect how much stress will be placed on the limbs and this affects how wide the bow needs to be.
Extra width adds a weight penalty that may reduce performance a bit but nothing else. Where the extra weight is located on the limb also matters. On pyramid style bows the extra weight is almost all on the inner 1/3 of the limb and has very little effect on the overall performance of the bow.
Mark
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Bowyers Bible vol 1 has a lot of information on bow design and will help with that on lots to f different woods. Don’t remember which chapter but I think it’s performance and design by Tim Baker.
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This is kind of a general answer and somewhat non-specific but I think it does cover it pretty well. Osage is usually about the densest wood. While most of the white woods tend to run between 60 and 70 sg. Osage is also more elastic than most and can be narrower, same with yew. Most figure for a 66" stiff handled 50# pyramid bow about 1 1/2" for osage and 2" for white woods. As you go longer or shorter you can add or subtract slightly from the width. I usually go about 1 1/4 for osage but if I go back to building I will lean more toward 1 1/2 in the future. Anything you do to shorten or lengthen your working areas should be allowed for. A bend in the handle bow can be much narrower for example.
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Very good summary, as exected, from Badger.
I would observe that for a given thickness of any piece of wood, there is a degree of bend that will produce compression fracture. Thinner will allow more bend before failure. Width governs draw weight.
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Good info. Thanks to all.
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Not all wood in a given species is equal. A particularly dense piece of whitewood will make a pretty narrow bow. Best to go with recommended widths till you know what the wood you’re working with is capable of
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Just finished a hickory bow that 64 inches. The stave is 17 years old. It is the hardest most dense piece of wood I have ever worked with. It dulled my tools in no time. I made it 1 1/2 at the fades to a little under a half at the tips straight taper, and sinew backed. It is 35lbs at 25 inch draw for target shooting. I bare shaft tuned a 600 spine carbon arrow with a 100 gr. tip that weighs 350 grs over all. 8 strand D97 string, and 5/16 deep cut out arrow rest. It weighs 24 ozs., and holds 1 1/2 inches of reflex. It amazed me that this piece of hickory is that dense, and rock hard. Maybe because it seasoned for 17 years. I have no idea.
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Good information guys. Bassman well done. I’m not a fan of hickory but that doesn’t mean hickory is not good. It’s broke records lots of times.
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Not a hard shooting flight bow like you make selfbowman, but it should suit my needs. I am going to shoot a 300 round indoors tonight. 74 years old now ,and can't handle to much weight any more. I will leave that to you young fellows. Good building.
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Very good summary, as exected, from Badger.
I would observe that for a given thickness of any piece of wood, there is a degree of bend that will produce compression fracture. Thinner will allow more bend before failure. Width governs draw weight.
That's it ^^^^^ this same sets of facts also determine what the tiller should look like ;) Tiller logic
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Here's a link to a post by KS51 from 2015. I've used it for years. It works-out really close if you know the specific gravity of your wood.
KS15 - a Formula for Limb Width (@the fades)
https://www.primitivearcher.com/smf/index.php/topic,53529.msg725728.html#msg725728
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Wow, I've been working on something damn near exactly like this for 3 years. I haven't said anything yet because I haven't finished proving it yet, however I feel close. His formula makes sense and is close to mine with a few key differences. It's always a surprise to find out that there is nothing new under the sun.
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Lots of folks say you cannot make a narrow limbed bow of most whitewoods. I have never made a bow with limbs more than 1 1/2” wide and made many that are 1 1/4”-1 3/8” wide. These are all parallel limbed bows for 2/3 of their length or so and taper to 1/2” or so nocks most have been 60”-66” long. I have had a few compression failures but most has held up. I’m looking forward to looking over that info on SG and see how it comes out on some of the staves that I have that I know will produce a narrow limbed bow, or at least the split right next to it did. Another side of it is saplings. A good hunting weight bow can absolutely be made from a 2” diameter sapling. After you take the wood you need off to make that sapling a bow, you aren’t left with very wide limbs, but it works. I think there are a lot of variables, from crown, bow length, density, limb shape, and probably more. I don’t think I could make a whitewood pyramid bow starting out with 1 1/4 limbs, but it might be possible with the right piece of wood. Most everything I make is of hackberry or elm, with hackberry quality varies greatly from tree to tree. You can cut two trees that started as shoots from the same stump and they will be different, I don’t understand why.
In the end, if you want your best chance at a shooter, go with a wider limb. If you have plenty of wood and time, and you want a more narrow bow it is worth trying, just make sure you get a good dense piece to start with.
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Just for the record, Tim Baker presented a chart of widths for a 50 pound bow made from maybe a dozen different woods in The Traditional Bowyers' Bible Vol. I.
To my knowledge, that had never been done before. Though it seems some of you are doing it again.
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Here's a google sheet that calculates the width based on KS15s formula:
https://docs.google.com/spreadsheets/d/1YGOuEcokwRiWDs7oGAn7y-Q56rM9f60iA9TI3cBk3hc/edit?usp=sharing
Give me a definitive guide to specific gravities of wood species and I'll see if we can make a dropdown so you don't have to look that up.
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Just for the record, Tim Baker presented a chart of widths for a 50 pound bow made from maybe a dozen different woods in The Traditional Bowyers' Bible Vol. I.
To my knowledge, that had never been done before. Though it seems some of you are doing it again.
It's good general starting points, but what I am trying to do is make a formula that tells you exactly the dimensions a bow needs to be for a given draw weight. I'd post it here but I don't want to post something I'm not done proving yet.
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As others have said, there is a lot of variation within a wood species. The best that can be done is to find an average of performance predictions. Baker's list does that. It's a starting place for the listed woods. Nothing more specific would be any more accurate.
The Forest Products Laboratories tested thousands of pieces of wood to reach their average of mechanical characteristics.
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As others have said, there is a lot of variation within a wood species. The best that can be done is to find an average of performance predictions. Baker's list does that. It's a starting place for the listed woods. Nothing more specific would be any more accurate.
The Forest Products Laboratories tested thousands of pieces of wood to reach their average of mechanical characteristics.
Well, like I said Jim, I have to prove it before I can claim it. However There is merit to what these guys are talking about.
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Here's a google sheet that calculates the width based on KS15s formula:
https://docs.google.com/spreadsheets/d/1YGOuEcokwRiWDs7oGAn7y-Q56rM9f60iA9TI3cBk3hc/edit?usp=sharing
Give me a definitive guide to specific gravities of wood species and I'll see if we can make a dropdown so you don't have to look that up.
This must be for a specific style of bow like a pyramid bow. That width seems overestimated in my experience with similar density woods.
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I think that bow width is really up to what you want from the bow. Osage will work well at 1.25" width but it will also work well at 2" of width. It's the same with all other common bow-woods. The suggested width for the different bow-woods in the Bowyers Bible are merely guide lines. All of them will work at narrower widths than suggested even at higher draw weights as long as you compensate with length
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Tim Baker did a nice chapter with a chart as a starting point.
As was mentioned above when I find limbs getting too thin then I begin to narrow them to bring the tiller home.
Jawge
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It's good general starting points, but what I am trying to do is make a formula that tells you exactly the dimensions a bow needs to be for a given draw weight.
You can't do that without measuring the modulus of elasticity for the actual piece of wood you are using for the bow. If you measure the MoE then you certainly can do a pretty accurate calculation of the bow dimensions.
Mark
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I like the weight I want to determine my baseline width, then I shift that width narrower if I want to make the bow longer for the same draw length, or make the limbs wider if I want to make a shorter bow for the draw length. The extreme ends I’ve done are a 50# at 27” hedeby style longbow only 7/8” wide and about 70” between nocks and bending through the handle and on the other end of the spectrum a flip tipped paddle bow pulling 60# at 27” with 2.5” wide limbs and 46” between the nocks. Both took about 1/2” set with the paddle bow still holding 1” reflex.
Kyle
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Any formula you used for width would have to include a lot of information that bow makers don't usually have access to. I don't think a formula would get anyone any closer than the common rules of thumb we all use.