Main Discussion Area > Bows
Stress and performance
Aussie Yeoman:
--- Quote from: Bob Barnes on June 26, 2022, 11:09:00 am ---
So, if you have the formula, and if it's not a lot of work, could you explain using Brad's 2 bow example from the above post? I'm just guessing that your formula involves coming up with the ideal dimensions for a given bow/bow wood...? thanks.
--- End quote ---
Yep, absolutely can do. Stand by for a day or two and I'll pul something together.
--- Quote from: Badger on June 26, 2022, 05:05:03 pm --- I think because all species and even individual samples of wood vary to such a large degree it is almost impossible to predetermine stress levels based on design beyond the standard rules of thumb we have come up with. You can fine-tune that a bit by monitoring set which is the ultimate practical limits of the bow anyway. But Ideally, I would agree that stress limits should be the same for any bow of any weight and design. Without engineering details on every piece of wood any practical useful chart to establish widths would be nothing more than the same estimates we use now.
--- End quote ---
Totally agree Badger. Fortunately, doing a bend test needn't take long. And the time it saves is immense too. I can make a longbow from a board that pretty much comes off the bandsaw tillered to within a couple of pounds of design.
Badger:
Aussie, 1st of all I wanted to publicly thank you for converting the mass formula to an excel spreadsheet for me many years ago.
As for a bend test, I was never able to convert a bend test to usable information that I could apply to making a bow. I think if you could lay out the method for doing this, if it is not too complicated it would be a huge step in making higher performing bows. I came out with several tests that were useful in comparing wood but I was never able to directly apply it to a design. Hopefully you can send us in the right direction here.
bradsmith2010:
the answer to your question is yes,, no graph or formula needed, just make the two bows and see for yourself,, its that easy
Bob Barnes:
--- Quote from: bradsmith2010 on June 28, 2022, 04:26:38 pm ---the answer to your question is yes,, no graph or formula needed, just make the two bows and see for yourself,, its that easy
--- End quote ---
Brad, I agree somewhat. but if someone can tell me that the shorter bow needs to be (maybe) 3" wide and 3/8" thick to be strained the same as a longer bow that is "1 1/4" wide and 3/8" thick... it would be interesting and a good place to make 2 bows just to see how they compare in reality. I guess I'm a visual learner....
bradsmith2010:
me too thats a good point,, I would be thinking is the mass of the 3 inch bow gonna effect the performance,,
I would just have to make it,, shoot it through a chrono and see,, I dont know the answer,
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