Primitive Archer
Main Discussion Area => Bows => Topic started by: DC on April 25, 2020, 12:52:50 pm
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Has anyone glued a wedge in the end of a billet instead of using a riser block? I'm mostly concerned about a weak spot at the end of the wedge. I glued this experiment up. It's an OS billet with a chunk of fir for a wedge. I just used wood glue. I grabbed it in the vise and gave a good reef on it. I gave a bit of a crackle on the first pull but was fine after that. Hopefully it was just a bit of bark or something. It won't be used for a bow anyway. With contrasting wood it could look OK. I might cut the kerf a little closer to the back or maybe start close to the back and slope it toward the belly so that the end of the wedge is close to the neutral zone. Ideas? Comments?
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I love the idea, but I'm concerned about splitting on osage, maybe if you got it hot first?
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I love the idea, you would just have to feather it in really thin? I think you should try it with a hard wood. Fir vs OS outside of the neutral plane might not be a fair fight. Keep up the good work sir!!!
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DC, I can remember a bow built like that and posted here. should be possible... cheers
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I love the idea, but I'm concerned about splitting on osage, maybe if you got it hot first?
I put a C clamp on the limb right at the end of the kerf to stop it from splitting there. That works well. I tried kerfing and then steaming a piece of OS but the back part cupped quite dramatically and then I couldn't clamp it together without it splitting lengthwise.
I love the idea, you would just have to feather it in really thin? I think you should try it with a hard wood. Fir vs OS outside of the neutral plane might not be a fair fight. Keep up the good work sir!!!
You only have to feather it out to the thickness of the kerf. In my case about 1/32"(1mm) thick. It may be better if you could feather it like a power lam but I haven't figured out how to get the kerf tapered to nothing. The fir insert was just a test on the end of a long OS billet. it will be firewood.
DC, I can remember a bow built like that and posted here. should be possible... cheers
I don't doubt that. I don't think anything is new in archery ;D
I epoxied one last night. I used a Black Walnut insert in an OS billet. After I finish my coffee I'll unclamp it, clean it up and post it. The other thing that is bothering me(beside breaking at the end of the kerf) is where to position the end of the kerf between the belly and the back so that after tillering there is still enough belly wood left. On this one I put it about 3/8" from the back.
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If that is in a working area of a limb I'd be concerned it wouldn't be able to handle the stress of bending.
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Yeah, that. :D I made mine 8" long which puts it about 2-2 1/2" outside the fade. Right in the highest stress area. If I made it any shorter I couldn't get any appreciable thickness gain in the fades where I want it. Because the joint is so long and the stress will just be on the last couple of inches I'm hoping it will hold together. Just for speculation what do you think would happen if the glue let go on the last inch or so. Everything would still be held in place. I guess it would be like a grain delamination. We'll see. This is a fairly long term project so don't hold your breath :D :D
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If the kerf is in the middle it won't break there. If the back and belly are proper material, the core could be a line of blocks glued end to end and it would work. All force on the neutral plane is shear.
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I put the kerf closer to the back so I have enough belly wood for tillering. Kind of an educated(primary school) guess. It would be similar to putting a power lam under a bamboo back sorta. I'll show you in a bit.
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If the kerf is in the middle it won't break there. If the back and belly are proper material, the core could be a line of blocks glued end to end and it would work. All force on the neutral plane is shear.
+1. The vast majority of the bending moment is dealt with in the outer skin of the belly and back. The core is simply holding the outer surfaces in shape while they carry the loads. The only thing I can see that may be a problem is cracking along the grain that starts at the end of the wedge.
Mark
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Here it is cleaned up a bit. It would look better if the insert followed the flow of the limb but this will tell me if it will live ;). I put the other bow in there just so you can see where things will be. It's handle is quite deep. I'll might have to glue a bit of riser on there but it will be out of danger of popping off.
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Have a look at a few glass bows :)
That is basically how I make all my glass designs. It definitely won't fail. Ideally you want the 'riser' in the middle of the limbs thickness.
Are you planning on having the handle made entirely out of the center piece or are you going to use something to join the two backs? Two self limbs spliced on? If you went with a boo back and a couple of cores with a belly (for the limbs) you could 'work out' your design more easily.
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I'll cut the splice into the fat end you see in the picture. Natural back and belly. So a self bow with an insert and a leather handle to cover all the crap :D I just glued up the other limb. Maybe splice it tomorrow then Tuesday we'll see how it looks.
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This has given me an idea for tips too...
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I think this is a really neat idea, hope it works out.
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Here's both. The newest on the left. With the opposite curve in the stave it's hard to get them looking the same. I'll work on that.
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That would make a fun looking bow :)
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The splice is done and curing.
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Here it is with a riser. It will be reduced a lot. The green tape is where the handle wrap will go. Sorry for the blurry pictures. It's early and I'm old ;D
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can't see why it wouldn't work, seems like an elegant solution to me
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OK here's the results. Not so great. I think the first two are a result of the clamping gluing process. They appeared right away. Even though I clamped it so it wouldn't split, it still did. OS is incredibly stiff so there is a lot of strain right at the end of the wedge. Maybe sanding concave sides on the wedge to spread the strain wood help. I'm also thinking that putting the wedge closer to the back, making one side thinner would relieve some strain. A little heat might help also but trying to steam the whole thing was a failure. The second two pictures are the other limb and only one side has a small split. I think it happened after I started tillering but it's small so I may not have noticed it. I was a bit of a coward and didn't make it bend too much in the wedge area. Anyway they were there for 90% of the tillering and haven't moved since the beginning so I'll make a string and shoot it a bunch. I'm thinking that with a more flexible wood like Yew it may not happen.
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I think you need to make them come to a feathered edge over a longer distance, just like a real power lam or the way the fades are done on a glass bow.
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I can't taper it out any thinner than the width of the saw kerf. Any ideas would be appreciated.
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Tip of the wedge needs to be in the center of the limb thickness--the neutral zone.
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Tip of the wedge needs to be in the center of the limb thickness--the neutral zone.
True :D
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Tip of the wedge needs to be in the center of the limb thickness--the neutral zone.
The problem with that is the neutral point moves as the limbs are tillered. What was on the neutral axis at glue up is no longer there once wood has been removed from the belly during tillering.
Mark
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I did a lot of looking at other OS bows to get an idea of how thick the bow was going to be at the end of the wedge. I got it reasonably close that way. With a high tension strength wood like OS I think it would be safe to move it closer to the back but only trying would prove that.