Primitive Archer
Main Discussion Area => Bows => Topic started by: huisme on September 05, 2013, 02:16:34 am
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I'm working with a lot of Oregon Ash, and keep getting 3-4 inches of set no matter how smooth tillering goes when I reach ~50-60# @ 28". Is this because the wood is just not as dense as the better woods, or is two months not enough for Oregon Ash to dry in near-bow form?
I admit I haven't done much heat treating since my heat gun broke, and I'm assuming that'd help some, but in the mean time I'm confused.
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First off, what are the demensions of the bow?
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I've made several, most recently a Z handled flatbow, about sixty six inches TtT, two inches at the fades to quarter inch tips, 55/26, took three inches of set.
My black locust bows are taking one or two inches while this stuff takes three or more. I know it's not the best ash, but doesn't that seem excessive?
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Ash is a wood that has a lot more strength in tension compared to its strength in compression. If a standard bow is made from ash it takes a lot of set. The way around this is to trap the back and I don't mean just a bit....make the back half as wide as the belly (obviously you need to adjust this ratio near the tips). Once you have done this then a good heat treating to a solid brown will turn this 'set prone wood' into a top draw bow wood.
I am currently making a 75# @ 30 narrow elb from ash and have just got it to 29 with only a shade of set by trapping and heat treating.
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Mike,
How wide would you make the belly for a standard bow? Thanks.
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Also worth noting the early to late ratio with ash. The early is junk and if there is too much of it and not enough late then it's going to be crushy n spongy. I have a mild DR ash bow that has awful early to late and no amount of heat or width stops it from taking a ton of set.
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Ash is a wood that has a lot more strength in tension compared to its strength in compression. If a standard bow is made from ash it takes a lot of set. The way around this is to trap the back and I don't mean just a bit....make the back half as wide as the belly (obviously you need to adjust this ratio near the tips). Once you have done this then a good heat treating to a solid brown will turn this 'set prone wood' into a top draw bow wood.
I am currently making a 75# @ 30 narrow elb from ash and have just got it to 29 with only a shade of set by trapping and heat treating.
And that trapped back will translate to thicker limbs for equal weight, right?
Trapping the back is one of the things I still haven't tried, so while I could just go try it out I'd like that little bit of info.
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Remember that generally, a bow twice as wide will be twice the poundage, a bow twice as thick will be 8 times the poundage. Trapping the back, wont take much more thickness to make up the difference.
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I tend to trap once the bow takes that first tiny bit of set.
I would probably rough out the max width to be around 2 inch.
Remember also that a high crown on a smaller diameter stave does the same job as trapping.
I once made a short,narrow ash bow. Completely rectangular because it was from a big tree. I then tillered it and pulled it about 10 inches too far.
The result was about 5 inches of set!
I then turned the bow on its side and cut it in half along the neutral plane.
The back half sprung straight again and the belly half took even more set.
That little bows back was never even close to breaking and the belly was actually being held in a position of less set by the back.
My conclusion = trap the heck out of ash and other tension strong woods ;) It works.
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Remember that generally, a bow twice as wide will be twice the poundage, a bow twice as thick will be 8 times the poundage. Trapping the back, wont take much more thickness to make up the difference.
No... not quite. Wood that is double the width will be twice as strong structurally, and double the thickness will be 8 times as strong. It has nothing to do with poundage.
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The point was to answer his question about trapping the back, losing the width and making up for it in thickness. Wanted to clarify that it wasn't a 1 to 1 ratio. It's far less than that. I'm not sure that 8 times stronger is accurate, but it's close enough to illustrate the point.
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When was the wood cut? I'd look to excessive moisture causing that amount of set. Jawge
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I use my moisture meter all the time but there are other ways to insure moisture content is where it should be. But I'll wait for your answer. Jawge
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It was cut two months ago, and I went ahead and trapped a longbow and it came out with one inch of set as opposed tot he classic 3+. Maybe I'll post it after it's finished.
Showed me how important trapping can be ::)
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I'm with Mike on the trapping I've built a couple long flatbows out of Oregon Ash that was seasoned 1 year and they both took some set. Maybe the wood was still a little wet then? I trapped them slightly but not nearly as much as the back being half as wide as the belly, and heat treated and they still took about an inch or so of set. They do shoot real nice though, one was 67"ntn and the other 60"ntn. The 60"er tood quite a bit more, especially where there were kinks on one limb, but it still shoots an arrow pretty well.
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It's still wet. Good call Jawge. let it dry longer. I rarely use a meter but only because my wood is dry, dry by the time I get to it.
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Auggie & I got 3 air dried ash boards from the Amish a couple years ago... 1 was edge grain, 1 was almost edge grain, like this/////, and the 3rd was good enuff to chase a ring on( and we did).. It was very flat backed from a large tree.We built them all to basic board bow specs.. 66" and 45#at 27"... The 2 edge grain were awesome shooters, and they only took 1/2-1" of set... The one with the chased ring took 5" of set(and i cooked the hell out of it) and was the slowest dog i ever built... If i had only known about trappin back then, lol... I guess my point is dont count ash out.. It shines when its edge grain! ;).... Brian
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Put it in a reverse form and let it dry