mollegabet board bow

[Knoll]

I have trouble seeing elliptical tiller when it's subtle. If you run the straight edge across the belly. With an eliptical tiller, the gap will gradually get larger as you move out on the bending portion of the limb.

Yep, that helps me too.

[Zedd]

Zedd elliptical or circular tiller the gap between the straight edge and belly should be even, a circle tiller may have more gap than ellitical but the gap should remain constant. I don't need geometric theory to know that if that gap isn't consistently the same the limbs aren't working equally from fade to fade

I apologize in advance as I can be pretty hardheaded in that it takes a bit to sink concepts into this thick irish skull of mine. You have given me something to think about. I was a nuclear technician in the Navy and the training has followed me my whole life. One of the consequences is I tend to over think things... That being said, I can think of a couple situations where what your describing would not be the case, however, I don't know if they would apply to this situation. What you are describing is a circle. If 'working' is defined as moving equally throughout the power stroke portion of the limb (pretty obvious where this would be on a mollegabet), then I did not do this. Am I understanding you correctly that you are saying an evenly bent or circular tiller (which is what that method would give) bow means the stress on the limb will be equal throughout the bend? Given two factors, the levers of the outer 1/3 of the limb and the support the fades will give to the working portion of the limb, I am sure this is not the case. That doesn't mean you are wrong in suggesting how to check my tiller though... I am not trying to be argumentative, just trying to understand the stresses on a this type of bow so I can minimize the chance for a catastrophic failure in the future (though this does shoot fantastic now).

[Zedd]

Ok Eric, after looking at what you said, I redid the ellipse and it seems you are suggesting a tiller a bit at the shaded in section here?

[bubby]

http://www.primitivearcher.com/smf/index.php/topic,23134.msg311835.html#msg311835

Build one of these it will take care of the problem

[High-Desert]

Yes! That is exactly what I meant. You can see it perfect with that drawing, and where you have red marks is where it need to bend most.
As far as what you said about stressed. The idea is to keep stresses even throughout. When limbs are parallel, the limbs in theory are thinner the further you progress out, thinner would can bend further than thick would, so your stresses are still "equal," when limbs are pyramids, the thickness is the same, so bend must be even, circular, to keep stresses equal.

[Zedd]

This is the difference between book smart and hands on smart! I have read these pages thousands of times, and only now after seeing what you two fellas are talking about do I understand. It makes perfect sense now! Eric and Bubby, thanks for your help. So on this bow as it stands, the highest stress level would be at the fades nearest the handle because they are working or moving more than the rest of the limb?

[High-Desert]

Glad to help. It's awesome would it just clicks.
Yes, so right now your limbs are being stressed the most at the fades and not sharing the stress with the rest of the limb. This can cause excessive set where you least want it.

Eric

[Zedd]

When you say fades, you are referring to the fades near the handle? What is the fade where it goes to the 1/3 outer part of the limb called?

[Zedd]

I was hoping someone could answer the question regarding the use of tanned snake skin as opposed to raw (untanned) snake skin for use as a second backing? Also, since I am going to do at least a couple more board bows before I plunge into the world of the stave, how much leeway do I have regarding the run-off on a red oak board, keeping in mind I will be backing it with rawhide? Finding a board with no run-off and the correct grain orientation is very challenging.

[bubby]

I've used tanned skins before i soaked in dawn soap water and rinsed no problemo

[willie]

very nice bow, especially with the white cobra skin. As for a recommendation for the best glue to use with the rawhide to snake skin joint, you might consider a contact type, rubber cement. Leather workers often use barge brand.

It is hard to prescribe a certain amount of runoff as acceptable, but I would look to minimize runoff angle, especially in the highly strained portions of the limb, and be looking for a board with high latewood ratio, or at least consider other  ring orientations besides flat, if using red oak or another ring porous wood. Raw hide as a fix for excess runoff is debatable. Certainly better than a something thin like a cloth backing, but not a cure.

sagitta is latin for arrow 

Ultimately, when tillering any bow, the appearance of set, early on in the tiller process, is the hands on way to ascertain the working limits of the wood. Although I can appreciate the technical understanding of stress and strain when fleshing out a design, when tillering, I find that tracing the back curve of the just unstrung bow very helpful to learn where the wood is heading towards becoming overstrained.

[Zedd]

I've used tanned skins before i soaked in dawn soap water and rinsed no problemo

That's exactly what I did, I even used Dawn! Thanks. They seem to be holding up ok. I trimmed the skin off flush with the edge instead of rounding the edge off. It would definitely look more polished with a rounded edge and I think the skin will have much less risk of lifting up.

[Zedd]

very nice bow, especially with the white cobra skin......
....Ultimately, when tillering any bow, the appearance of set, early on in the tiller process, is the hands on way to ascertain the working limits of the wood. Although I can appreciate the technical understanding of stress and strain, at least with design considerations. When tillering, I find that tracing the back curve of the just unstrung bow very helpful, when set first becomes detectable.

Thank you. The skin is actually a metallic steel or silver color. It was very shiny, like you could use it to warn away aircraft shiny. I stained it with a coffee brown stain I had from an old job and it took some of the sheen off. I am more a natural color kind of guy.

I don't understand the last part about tracing the back curve. How does tracing the back curve help? Again, my ignorance is showing.

[scp]

Congratulations for the incredible first bow. Even for a Mollegabet style bow, the easiest way to tiller the working limb is to give it pyramid front profile. Maybe next time.

[Zedd]

Congratulations for the incredible first bow. Even for a Mollegabet style bow, the easiest way to tiller the working limb is to give it pyramid front profile. Maybe next time.

I might even look more graceful.