Concave limb tillering

[Yellarwoodfellar]

I just have to say first that the wealth of knowledge here is unfathomable. Now to the topic.
 Some months ago I made a 62 inch pyramid sage bow that was drawn full to compass at 28 inches and 62 lbs. This particular bow had a mildly radiused belly heat treated and three and a half inch stiff tips. The bow was probably the fastest I've ever seen but in my immaturity I decided it needed a shelf and that was the greatest exploding I've ever seen in a bow lol. Here's the thing, the only difference in that bow was that it had a concave back almost exactly two inches into each limb. Did that make the difference? If the whole limb was concave would it increase performance? Is there a certain way to profile such a limb to take advantage of some extra energy? Thanks for the brain fodder!!

[willie]

concave back? would you be kind enough to describe the handle? Bendy? Narrowed? Not sure if I know the answer to your question about performance, but there was a concave backed bow posted a while back.
Did the back separate at the ridge you cut for you shelf?

[Yellarwoodfellar]

The handle was stiff bulbous and slightly sculpted. Fade to fade was 8 inches with a cup running from two inches past the fades to the center. Yes the poor thing sploded by splitting right where I started the turndown for the shelf notch.

[George Tsoukalas]

I had the same thing happen years ago so I don't usually cut in shelves. If you do, it can't be an after thought. You have to make the handle thick enough especially if you are going to cut in towards center.

Can't help much because I usually just glue on some pieces of leather.
Jawge
http://traditionalarchery101.com/leatherhandle.html

[PatM]

Sounds like the bow had a  back with the highest spot spit in two on either side of the fade. That would make those the areas under most tension stress and add to the weakness of a notched out area.

[Yellarwoodfellar]

I seen the error in the aftermath but what made that particular bow so much snappier than other bows made similarly? Did the concavity stiffen the limb faster as it straightened? Seriously the bow was amazingly fast with a 10gpp arrer

[willie]

http://www.primitivearcher.com/smf/index.php?action=profile;area=showposts;u=20229

it was discussed recently in some of these threads

[Yellarwoodfellar]

Thanks, Willie. However I could only find readings on a hollowbelly design. I didn't find anything about a cupped back.

[PatM]

Several of those posts say "hollow back".
 

www.primitivearcher.com/smf/index.php/topic,62468.0.html

[Yellarwoodfellar]

I see that! Thanks Pat. I think that's one of the neatest bow I've ever seen. I wonder if a concavity like that would perform better still if it were a single growth ring?

[Yellarwoodfellar]

Thanks George! I've tried using a broken stone point in that same context. I turned out ok but the leather obscured my idea! I think I will try again with a relieved area to set the point in that way I can hopefully exposed more of the Arrowhead.

[Yellarwoodfellar]

The question here is wether or not a natural concave back would be the holy Grail platform for an unbacked selfbow? Hope this stirs great debate!

[willie]

Some woods seem to do well with a trapped back design while others might be the opposite. I suppose that materiel selection is as important as design. Do you have naturally hollow backed staves? or are you proposing to make the back from the middle of a sapling?

[Yellarwoodfellar]

I've had several staves with a cupped back n all wanted to crack on the ridges to the outside of the limb save that one bow which was wicked fast. Quite different than a trapped back. Just a natural canoe for a back

[Yellarwoodfellar]

I want to think that it would want to curl upon bending making for a higher weight with less wood. If that were true then I could see why that bow was so snappy.