DIY Bow Project XI – Pop!

Well, I think I’m going to grab my shotgun and Winchester and use them during this hunting season. The time is getting short and I already scarified the start of the duck hunting for my bow project. For one week now, I have just build my lyly bow, from the now dry stave I mentioned in the previous post. The days have been really long and it was sooooo promising bow. Now, I’m a little bit wiser again, but without a bow, unfortunately.

Even with superior materials, like with the lyly wood and Dyneema rope in my case, making a serious bow is still like making a pocket watch. I tried to be as accurate as possible, why the back and the belly of the bow were really smooth, but not enough even in thickness. By scraping with a knife, I managed to polish the surfaces really well, simultaneously tillering my short bow, but the other limb was not as even as the other one. Before the knife, the initial smoothness should be made with a rasp or a plane, because the short affecting range of a knife will only follow the initial, rough topology of the material. I saw a hinge in the poorer limb. I noticed it, I concentrated on it, but still I didn’t pay enough attention to it and didn’t fixed it enough early. That is why the bow exploded during one pull! Too much energy in a small bow (120cm ntn) with a hinge, although it was only just over a 40lb pull 😛 You can see from the coming images how many pieces the bow shattered into, just because of a little unevenness. But again, I learned a lot!

As a (couple of) note(s) to myself.

If there is something uneven in the bow, it should be fixed as accurately and soon as possible with appropriate tools. Rasping with a knife will give you a really smooth surface and accurate way of removing wood, like adjusting and finishing at the same time, but the primary smoothness should be made with the tools having wider-affecting-range. It is super hard to flatten major hills and valleys with a knife.

“The good materials will forgive” is a wrong attitude, and many pounds are lost if the bow is balanced too late. If there is a hinge, it can “escape” along the process, if the removal of the surrounding wood is not enough aggressive. If only microscopically thin slices of the wood are removed, and the bow is bend for testing, the hinge will become worse as the hinge wood tires further.

As a beginner, I should not heat bend deflexes in the limbs next time. When a deflexed bow is bent in the tillering tree, it is really hard to see, is all the portions bending evenly, or are some parts statically already curve. I believe that in this bow the effective working length of the limbs was much smaller than the designed one, and this might be the biggest mistake I made.

I also baked the limbs from the belly with a heat gun for 40 min, so that the internal resin “cells” would melt, became connected to each other, and make the bow harder after the spontanous polymerization and cooling. Many people say that the baking is like magic, it increases the pounds, makes the bow tougher, it even smooths the bending, but it will also decrease the tensile tolerance. I got only 4lb increase, and in my case the heat might went through the limbs and make the back more fragile, even though I constantly tried the back temperature by my hand. It would be a good idea to cool the back of the bow actively during the baking process, as the rearrangement of the internal resins seems to be a clever way of increasing the belly stiffness against compression and for evening the stress.

Adding more initially really tight Dyneema rope could give the needed extra support for the back of the bow. If we assume that the baked lyly wood is extremely resistant to compression failures, like it should be, but the baking might make the back a little bit more fragile for tension, then the Dyneema rope cannot be too tight. The twists of the rope will eventually add the effective length of the rope per a constant length, meaning more elasticity, and more individual ropes will share the stress. Furthermore, as a synthetic polymer Dyneema will eventually act like a rubber band under extremely high strain.

For increasing further the tensile resistivity of the back, it would be wise to dig out one continuous line of cut-through growth rings while preserving the flat back. If you look at the coming photos, you see that there is a pattern of changing layers of growth rings in the back of the bow. Every transverse transition between different growth rings could act as a potential origin of failure. Even though the growth rings are needed to be cut in flat bows, these transverse steps of growth rings could be avoided by proper cutting of the tree. From this point of view we can go into a second thought I had. For avoiding the previously mentioned hard-to-recognize-static-bends problem, after digging out the smooth back with the only-parallel growth rings, the bow should be heat bent for making it straight as possible. If the working parts of the bow are straight in rest, it should be much easier to see, does the bow work evenly; every part has the same starting point in the beginning of the tillering process. Thus, after digging out the back with the good growth ring patterns and heat bending the bow straight, the steep shiyas (sakara in Finnish) should be made.

Before bending anything, it is wise to ensure that the opposite parts of the bow are equal. For example, if the upper limb of the bow is thicker before bending than the lower one, it will experience more stress during the bending, making the limbs mechanically different at the beginning. I prefer for using steam for bending, not a heat gun, because with the steam the temperature cannot go too high and make the bow fragile so easily.

Finally, I was too impatient as I waited only for one night after the baking. The bow might be too dry when I bent and broke it.

In a nut shell, as a person living in a modern society, where everything is instantly available, I should remember to take even more time for my coming bow projects and increase the accuracy. I believe that making a bow is like hunting with it, it needs a huge amount of patience and experience. For the coming two months, I’m going to rest, concentrate on hunting and hiking. After that, I will search a new lyly pine, the one which is already waiting me somewhere in a dark and silent forest 🙂 Thus, I will have a lot of time for adjusting arrows and practicing for the next hunting season.

Here are some photos from my promising, but now broken lyly bow, enjoy!


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This is how I search hinges. I pull this piece of wood along the belly. By the elevation of the block I see how the limb curves. Unfortunately, this is not a reliable method in deflexed bows.

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From this photo you can see that the right limb has already given up a little. This photo was taken just before the bow exploded.


Boooom, the whole limb shattered into pieces. I don’t know, was it because of a tensile or compression failure, but with the mentioned tips I will one day make the bow. So far, I will dream about it. 🙂


One thought on “DIY Bow Project XI – Pop!

  1. Thinking about this bow afterwards, I realized one important thing. Because of the hinge I saw in the other limb, the bow didn’t share the stress evenly. At least the other limb bent a lot of more from its base than elsewhere, and it bent further than the other limb. Thus, the stress was concentrated, and the effective working length was shorter than designed, like noted above. This makes me a little happy, because still the bow tolerated so many aggressive draws with the concentrated stress burden! So, by careful and even tillering, I really should manage to make a short and powerful bow with these materials 🙂 And one interesting sing about the presence of this deadly hinge is the small increase of draw weight after the baking. See, if there would have been more working parts in the limbs, the new connections and polymerization processes of the internal resins should increase the draw weight much more, like promised in many other internet sources. Now, only a small part of the total available resins took part into the hardening of the bow, and the increase of draw weight was small. Good to keep in mind next time. These naps in a forest help me a lot for processing things inside my head 😀

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