Primitive Archer
Main Discussion Area => Bows => Topic started by: Marin on September 14, 2022, 05:14:14 pm
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Hey,
I have not posted in a while but have been experiementing a lot. I recently had an issue and was curious if anyone else had any ideas. I was making a beautiful little short bow I had sinew backed with two layers of sinew. It was a replica of a central Californian Miwok bow, which were already narrower compared to the more northern "Paddle" bows. I used a spare piece of ERC I had that I thought I wouldn't be able to use for anything else, as it was rather narrow and had a bad hairpin grain. While shaping, I accidentally made one of the limbs slightly narrower than the other. It was not a major difference and still within the threshold that is known for these bows, so I thought it would be fine, so long as I watch it when I tiller.
The bow itself was short at around 43" with working recurves, with the idea of getting about a 19" draw length.
I began tillering the thing and was getting a nice even bend throughout, with both limbs bending about the same amount. Once it was bending at about 6 inches or so with a long string, I thought it would be ready for low or medium brace. I was working with a friend who has made more bows than I and we both thought the tiller looked fine and that it was ready. Once we strung it, the tiller still looked perfect, but a large chrysal developed in the middle portion of the narrower limb. We were both confused as the tiller did not seem to indicate that this region was bending anymore than the other limb, nor did this limb portion have a hinge in any way. The only thing I can think is that the narrow design, which has a rounder cross section, was just too crowned for the bow at this width. But this also is a little confusing, as these bows were made rather narrow in the first place and the bellies were always rounded in that manner.
I'm thinking one of two things:
1: the narrower limb, despite bending the same amount as the wider limb, was taking more strain in the bow overall for the amount of width it had. The recurves, which were bending quite a lot during the long string, took less strain once I strung it, thus focusing more strain at the center of the limb where the chrysal formed
2: the bowwood, ERC, while being mostly identical to juniper was perhaps not as well made for compression as Utah Juniper or Incense Cedar, the material the originals were made of, and is thus not as well equipped for the narrower design of these Central Californian bows.
I have pics of the bow's tiller shortly before the "disaster" which I can post if ya'll want to see. And like I said, I had a second pair of eyes on the tiller when it happened. We are both confused as to how this happened, and while I can't fix it, it has been a puzzle for me in the last couple of weeks, and I would like to actually learn something from this. Maybe someone else has an idea?
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Hairpin grain(worst culprit), with a narrow limb. Combine that with a short, highly stressed design = problems.
Without the dodgy grain it probably would have been okay, and free from chrysals.
Grab a clear stave and get at it.
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Yes, Marin, please do post the pictures. Jawge
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Here are some of the photos of the bow, including my most recent tillering photo before I strung it. Unfortunately don’t have the strung profile, but all I can say was the inner limbs were bending evenly and the recurves were not stressed. It matches what I see in historical photographs of strung Miwok bows
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More photos
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And sorry about the photos, some of them have been compressed so the bow looks a bit shorter than it is.
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Also, why exactly would the hairpin grain cause problems? I thought it wouldn’t do anything compression strength wise
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Anything like figure, or knots, or other anomalies of grain doesn't seem to be as tough as regular straight grain.
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So you haven't strung it, Marin? Hard to tell tiller without a strung bow.
Anyway, chrysals that are localized are indicative of a bad tiller or perhaps another problem as mentioned above.
Chrysals that are spread out over the entire limb or so are indicative of a design problem...too short...to narrow...to heavy for the wood, etc. So do check that please.
Jawge
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I had strung it. I just didn’t have any photos of the strung profile. All I can say is having a second person there with me when I strung it, someone who was more experienced than me too, we both checked the profile and saw nothing wrong or obviously wrong with it.
There was only one Chrysal though, so I guess that means that particular area was weak in a different way. I guess it had more to do with the hairpin grain.
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How much weight were you pulling on the bow in the pic where you have the long string on it?
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I could be wrong but it looks like the handle section is narrower than the limb. If it is bending evenly then that area will be more strained than the wider portion of the limb. Looks quite narrow even if it is representative of preexisting bows.
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Badger: if I remember right I think it was pulling just under 20 pounds with the long string, maybe closer to 15.
RyanY: yeah the photos are bad. The handle section actually isn’t narrower than the limb in this case. These bows were more akin to D bows in overall profile, with the handle being the widest point. Also, the chrysal did not happen in the handle but closer to the mid section of the limb.
And you are right, this design is surprisingly narrow, especially compared to other California bows. I think it was most likely because it was often made from branches which were already narrow and had a rounded shape, though it is also possible it was made from larger staves as well. To give you scale, the handle of this bow is about 1.2 inches, or around 30 mm. Based this measurement off of a stave they found in the Coso mountains of Eastern California a couple years ago, also made of juniper and also with a rounder cross section.
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maybe the photos were a little large when you loaded them,,
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Yeah not sure how to improve them. Are you suggesting upload smaller photos?
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A possibility I was thinking about was the fact that the bow was sort of asymmetrical in profile. I accidentally made one limb narrower than the other. Could it be possible that this led to the narrower limb taking more strain than if both limbs were of equal width?
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Forgot to add this but I found an example of the strung profile as it looked. This was the target I was going for so I was quite excited that the strung profile almost perfectly matched this one....... before it chrysaled