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Curly BBO build along
bobnewboy:
Hi All.
Its been some time since I did any making, bows or arrows, but once the bug has taken hold it is difficult to shake off 8) . Especially with all you guys posting pictures of such fantastic pieces of work.
I've made two BBO bows (both posted on here), and both have worked out really well, so I thought I'd try something different, and perhaps a little more technical. I decided that I would make a short reflex-deflex BBO bow, like a horse bow, which should be well suited to field archery here in the UK. I'm hoping for 50-55lb at 28 inches, but I know from reading posts on this forum that reflex bows are very difficult to tiller well, and can be rather deceptive during tillering. So fingers crossed, and here goes....
First job is to make a former around which I'll bend the recurves. I have a mildly shaped former for setting back the handle area on my previous bows, but this is not nearly tight enough to make the recurved limb tips I want. So I bought a large piece of 2x4, and drew a natural tightening curve on it. I cut it out and added some clamping holes. I then cut the curved end off, and screwed and glued it to the remaining piece of the 2x4, making a step upon which I could rest the limb being bent, hopefully keeping the bent section in line with the rest of the bow.
I then tried bending an example piece of 0.25" seasoned osage with dry heat from a hot air gun. This went well, but I noted that wood scorched a little, and that any loose fibres burnt and discoloured rather easily. See the first pictures:
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bobnewboy:
Okay, so having read some more on the forum about bending osage, I decided that it would be worth going ahead, but using some kind of natural oil to avoid the scorching of the wood - I chose olive oil as I already have some. I also got the belly piece to a floor tiller with a good thickness taper, and made sure that all edges and surfaces were rubbed down with sandpaper. I did not taper the sides of the limbs, so that while bending the tips I could be sure that I didnt pull the limbs to one side or the other, since it seems that limb tip aligment is a common thing to have to correct during or after tillering.
When cooled down and released from the former, the osage sprang back a little, but not much. There was still a little scorching, but this was no real problem as the affected wood would be removed when tapering the limbs. Here are the pics of the limbs being bent on the former:
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bobnewboy:
Having bent the osage belly piece, I found that the bamboo backing piece was fairly unwilling to bend into the tight recurve at the end of the limb tips. This is a nice piece of bamboo, with a good distance between the nodes (12" or so), so I wanted to use it. More reading on the PA forum...... ;D.
Ah, ok, bamboo bends with dry heat too! So I began by thinning the backing strip as much as I dared on my belt sander. The handle area of the backing strip is now around 3/16" thick, but the tips are around 1/16" - very thin but still seems strong. Then I used the former again, and gently heated the backing strip into the same curve. The bamboo sprang back a fair bit more than the much thicker osage belly, but it was now possible to fit the two together.
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bobnewboy:
So now I had the belly piece bent back into recurves at the ends, and the backing piece gently recurved. In order to make a R/D curly bow I needed to introduce some deflex in the handle area. I did this by dry heating (with olive oil) the handle area over a block with the good ol' heat gun, while tying down the limbs to the back of my recurve former. It makes for a nice shape.
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bobnewboy:
Now that I had the parts ready, it was time for the glue up. I prepared the wood surfaces by sanding with 80 grit sandpaper to give a fresh wood surface and a little surface key, and then wiped the surfaces down with plenty of acetone. This draws the oils out of the wood surfaces, especially the osage. I protect the backing piece by covering the waxy outer surface of the bamboo with self adhesive paper masking tape - makes cleanup after gluing much easier.
The glue I use is a resourcinol resin two pack type, originally known in the UK as Humbrol Extraphen, but now sold as "Polyproof Waterproof Glue". I measure it out by volume, and mix it using a piece of hooked wire in a hand drill. Its nasty stuff, so keep it off your hands and clothes. There is no solvent for this stuff once it starts to set! :o
I buttered both pieces of wood with glue, and then held the pieces together at the handle area using a g-clamp. I wrap the whole thing in cling film to avoid too much spillage. I then checked the alignment of the pieces, and then when all is OK, I begin the binding by tightly wrapping pieces of split bicycle innertube round and round the pieces. I start wrapping from the handle area outwards towards the limb tips. A good tip for UK-based bowyers - Tesco sell 26" wheel innertubes of reasonable quality for £1.86 each right now - I bought a few extra for the toolbox....The inner tubes provide constant even clamping pressure all along the glue line, and hopefully this avoids any dry spots or overclamping. At this point I set the bow aside to dry in my shed for a few days - it is nice and warm/dry in there at this time of year.
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