The last few days I've been working on a 3 piece takedown longbow using bamboo/jatoba/bamboo for the limbs.I had this idea that I had to try for the limb to riser joint.I cut dovetails into the limb butts and into the riser where the limbs seat.Then I made a bowtie shaped piece to fit in between and tie the parts together.The bowtie is glued into each of the limb butts and slides into the dovetail in the riser.I also drilled through the joint for a bolt 1" in from the ends of the limbs.Things went well as I began to tiller the bow but I soon began to hear creaking noises as I worked the bow on the tillering tree.Then I noticed that the lower limb had developed a crack at the end of the dovetail near the through bolt.I'm wondering if this is something I should try to fix or should I not risk it?
(http://i1177.photobucket.com/albums/x349/1wood1/IMG_0322.jpg)
(http://i1177.photobucket.com/albums/x349/1wood1/IMG_0324.jpg)
(http://i1177.photobucket.com/albums/x349/1wood1/IMG_0321.jpg)
In the close up you can see the cracked areas circled in red.
Should I just hang this one up and call it a lesson learned?
Dave.
WC2-
Surprised no one has dared an answer to your post so.... heres my 2 cents....
Not sure of how much weight your trying to pull on this bow.
If it was a light weight bow and it was mine I would probably fill the cracks with super glue and then ON A TILLER TREE, Give her a few pulls to see what happens?? Stand way back....
As I see the construction technique, The limbs or limb butts where you placed the butterfly joint were violated. probably 95% of the strength is needed to pull the bow back in that area so in this case the stress is right on the BF joint which failed. (The bolt holds the Dovetail wedge tight but the glue holding the limb butt to the wedge was not strong enough).
I would not violate the integrity of the limbs or the limb butts other than drilled holes (we see enough cracking here even with just those)
Disclaimer I am not by any means an expert in the field but would love to see the other guys here chime in, to further your passion..
Regards
I wouldnt try to fix it, thats just me. That joint has more stress on it than any other piece or area of that bow.
I'd make some new limbs...that area looks too thin around the bolt. If it was thicker and non-bending it probably would have held up fine.
Thank you all for your advice.I was wondering if superglue might fix it but I was worried that it was too big a crack.This bow was to be fairly heavy, about 55# to 60# when finished so I think I'll hang this one up and make a new one.
Either a 2 piece or another 3 piece with conventional attachments.It didn't cross my mind that cutting dovetails into the limb butts would weaken them.If I were to make new limbs for this one I might end up with the same problem.So much for being an inventor.It's not worth a slap in the face with a piece of sprung wood.
Thanks again for your thoughts.
Dave.
Don't beat yourself up for a "failed" invention. That is how new and improved things come about. Keep pushing the envelope and maybe you'll hit a bullseye, one of these days.
Thanks Razorback,I don't feel too bad about this bow.It was an experiment and I did learn from it.I like the combination of jatoba and bamboo.Before the limb cracked, it was pulling about 45# at 12" draw on the tree.I was about to go see if the garden centre has any more bamboo poles so I can get started on another one.
The only problem I have is getting good bamboo.
The poles I am able to get are only 3" or so in diameter.This makes it a bit hard to flatten them for laminations.If anyone knows of a good source of bamboo in Canada I'd be obliged.I would order from the U.S. but they charge a bundle to get it across the border.
Dave.
Ok here is a brainstorm Dave, I have never done a glass or lam bow. But I like what you have done, heck i was wondering when I seen if if you could not put in say metal dove tails and leave it with that. To save that bow I would just cut the dove tail off the riser and glue it in to the lam but. Then just use the tradtional methods of securing to the bow. Just a brain storm.
Good luck with the next build.
Kelly
The butt of the limb is where the most force is happening - the end of the lever. If you look at most take down systems either bolt up or pocket (like bear latch system) the limbs are very thick and not bending at butts. Cutting out that much wood for the dovetail is likely to lead to failures like you have. Kudos for trying new stuff and seeing what happens. I heard somewhere that "experience is a long series of non fatal mistakes."
I'm not worried about saving this bow.All it really cost me was some time and right now I have plenty.I never realized how much stress there is at the limb butts.I thought it would be evenly spread out over the entire joint area.The dovetails seem to be a fatal flaw and I don't want to fix it only to get hurt, or worse, have someone else get hurt.Maybe it's not such a great idea to be mixing furniture making with bow building.After my last post,I went down to the garden centre to see if they had any good bamboo left.The poles they have left are only about 3 1/2" diameter but I got the two best ones and I've already cut one down and planed 2 strips for my next try.
What I think I will do is build a bow similar to the first one but I'll use jatoba instead of walnut and I should end up with a heavier draw weight.That was basically what I did on this failed bow and it was coming out to be a strong one.
I don't pretend to know a lot here,I'm going by 1 successful bow and what I've read here on the forum so please keep coming with your ideas.I'm learning a lot and having fun.I've read that jatoba can have problems too,but it"s also a very strong and springy wood.(plus I have leftovers from our floor).
Dave.