Primitive Archer
Main Discussion Area => Bows => Topic started by: maatus on March 31, 2016, 07:33:06 am
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Do any of you have any experience with compression spruce (Picea abies / Picea obovata)?
Few days ago I tried compression spruce as a belly. I glued the birch on it's back and a light sinew cover on birch. Then I tried bending it towards my knee before I put the string on, just like I always do. I pulled some and then the spruce failed, a big hinge and then it completely broke. Luckily the birch part didn't take any damage. The belly surface was sanded to nice and clean, not any toolmarks or bugs.
I still got some compression spruce and soon getting reindeer leg sinew. What do you think of this combo? Is it worth it or should I just go and pick some juniper?
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Well since compression spruce ("kremlin tr.") was used, according to Russian lit, in some traditional two-wood bows, just a suggestion to look into for possible causes:
Belly lam too thick for the bend
Back lam too thick for the type bow
Belly-to-back ratio wrong fo the type bow
Sectional shape wrong for the type bow
Compression wood not of correct quality, density, cut, etc.
Birch of wrong type or quality
Heat treatment (or none) incorrect for the type bow
Wood flaws at the location
Moisture level too high for belly, or too low
Moisture level of back too low
Sinew application, or proportion incorrect for type of bow
Since it seems to have worked at one time for traditional bows, you have to find the missing piece of the puzzle in troubleshooting.
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I think the possible reasons could be
- Moisture level too low for belly
- No heat treatment
If the compression wood has to have some moisture in it, what do you think of sinew back, how it's going to be?
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Rings and the belly that broke
It was near the tip where it failed, like 10-12cm towards the handle
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http://paleoplanet69529.yuku.com/topic/29305/NorthEurasian-laminated-bow?page=1
this is an excellent thread about compression pine/birch bows of the north. most the pictures are gone (unfortunately). also ignore the rantings about the bow being too light of draw weight to make the design worthwhile.
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Sorry Markus, but I only have the questions for you to possibly look into, not the answers. You're the man for answers, eventually when you work it out with these materials!
One thing I have noticed in illustrations of two-wood bow sections (and they might not be accurate) but they appear to be quite rounded -- elliptical in shape. And it looks like the birch backing is thinner than the compression belly. thickness And so, because of the elliptical shape that makes the back lam actually narrower than the belly wood. The top of the ellipse cuts the birch lam width off. If the width of the compression wood is greater, it can be thinner, and less subject to chrysalling
Like I said, the illustrations may not be accurate and may not apply to the Russian spruce belly bows specifically -- so take this all with a grain of salt. It's a question, not an answer......
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Posts crossed,....... I just noticed you mentioned it broke close to the tip -- like within 4".
Many of the traditional two-wood bows I've seen discussed online and in arch. references have solid birch tips -- the birch back lam usually has a notched hard transition. Maybe a good reason for that tradition -- what was the construction of yours?
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PlanB: Sorry it took that much time to answer. I simply glued them together both having the same lenght. Then I glued the separated tips.
I'm gonna try again soon, will post the results here then.
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So I started working with it again.
It seems that it really needs some moisten in it or otherwise it will be too brittle and will break. I've been moistening the belly with wet rag every now and then and so far it seems to bend pretty nicely. I did glue them (birch and spruce) together with gelatine powder glue and it holds, but just have to be sure not much water goes into the glue line.
It's funny to see how fast it reacts to moisten and starts getting even more reflex.
I'll post some pictures later
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That tetrazolelover guy on youtube may know a fair bit..
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loon - I've watched his videos and did read those comments. It helped a lot.
First picture is what it looked like before. I did moisten the belly every now and then during the scraping process.
Then I steam-heated some curve on the ends. Second picture is what it looked like when it was completely dry.
Third picture is after moistening the belly for 6-8 hours. Most of the reflex came back but not all of it.
All of this happened only by moisture changes... It is very interesting wood indeed!
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It works - if not overdried and compression wood not being too thick. Birch (Betula pubescens or pendula) back and spruce (Picea abies) belly. 110cm, 38mm, pulls 55-60#@20". Linen string with birch bark covers. Brown leather wrap on handle. Sorry for bad quality pics...
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Few more pics
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That looks great! That's a neat little bow! I too have experimented with his combination from time to time but have never had much luck. A question for clarification: did you steam bend the tips after you glued the birch and spruce together? Didn't the glue line fail from the moisture of the steam? And also, I looked up tetrazolelover on youtube but couldn't find the video(s). Would you mind sharing a link? Thanks!
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Thanks Frodolf!
Yes it was already glued when I steam-bended some. I wrapped some linen cord on the tips before and it seems to hold just fine.
I fixed the tiller a little bit and now the whole bow is wrapped with birch bark and is stored outside all the time for experiment. So far it has been OK and no drying noticed.
Here's the links:
https://www.youtube.com/watch?v=ibX_0LgbTEw
https://www.youtube.com/watch?v=7O4_f052syc
https://www.youtube.com/watch?v=qzfqzSzjqsA
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Markus-
tricky stuff to work with. success at last!
and a nice looking bow too.
will you try another? maybe with a full draw?
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I would think you would want a branch of old growth spruce for your best chance. I've been looking for a such a branch of Doug fir for a sinew backed bow. Since I've found Incense cedar to be the best compression wood so far, I would like to try some other less used conifers. By the way I found the best incense cedar is from the natural reflexed top of the branch with very tight rings.
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I've thought about that. The top limbs from big old Doug Fir are like stone.
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Got me wanting to break out my cottonwood bow I started awhile ago lol nice job!
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First when it was finished, I wrapped it with birch bark and stored the bow outside. It didn't work that well, it kept drying and were brittle and weak due to that. Then I took birch barks away and noticed a longitudinal crack at the center of handle. It started spreading if it was too dry so I had to keep it as wet as possible.
Then I found that pitch was used to make the compression wood more durable. Yesterday I then saturated the belly with (spruce) pitch. It is now drying and so far the bow hasn't gone deflex at all.
Going to post the results later...
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Interesting stuff :)
Pitch is normally (any pine) resin heated until you get rid of the volatiles then mixed with powdered charcoal.
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I know you can mix it with different materials but I've no clue should it be done on this
I'm sure this pdf file would answer many questions just if it was in English...
https://docviewer.yandex.com/?url=ya-disk-public%3A%2F%2FWh0XdGgonCs9kl3ZjDuVveFUDqbQVUx5T2yIkCMSArQ%3D&name=%D0%98%D0%B3%D0%BE%D0%BD%D0%B8%D0%BD%D0%B0_%D0%98._%D0%92._%D0%9B%D1%83%D0%BA_%D0%9E%D0%B1%D0%BB%D0%B0%D1%81_%D0%91%D0%B5%D1%80%D0%B5%D1%81%D1%82%D0%BE.pdf&c=576800ec1a7d (https://docviewer.yandex.com/?url=ya-disk-public%3A%2F%2FWh0XdGgonCs9kl3ZjDuVveFUDqbQVUx5T2yIkCMSArQ%3D&name=%D0%98%D0%B3%D0%BE%D0%BD%D0%B8%D0%BD%D0%B0_%D0%98._%D0%92._%D0%9B%D1%83%D0%BA_%D0%9E%D0%B1%D0%BB%D0%B0%D1%81_%D0%91%D0%B5%D1%80%D0%B5%D1%81%D1%82%D0%BE.pdf&c=576800ec1a7d)