deflex and reflex theory

[SLIMBOB]

Very interesting discussion, and this is a topic on which the answers have never seemed entirely complete.  I came to the the whole D/R party late in the game.  After building a handful of them over the current year, it was pretty obvious that the design does offer some real improvements over a reflexed bow.  The why has been fairly elusive however.  I think Arvin nailed a few of the key aspects so far as I can pin them down.  Moving the bend outboard, getting the tips lighter and thereby reducing set, which cripples a bows performance at some level.  You simply, so far as I can determine, have less wood moving a shorter distance, which increases the efficiency, coupled with the bow taking less set as a result.  That's a winner in and of itself.  But it doesn't tell the entire story.  Glass bows benefit from the design without reduced set being a factor.  I think you can go shorter with a D/R than it's reflexed counter part without suffering the consequences as early.  Still not the entire picture though.  I don't yet understand the differences (and may never) but I appreciate the discussion.   

[Stick Bender]

Slimbob is right this topic is really interesting to illustrate some of the advantages of the design I will post this bow granted its glass test bow but all the same principals apply & Im planing a similar design in sinew/horn composite with less aggressive bends but I have made 10 of these over the last year different riser/ handle lengths & different working limb lengths & many different power lam wedge tip combo's & and different amount of reflex and tested performance on all but this bow is short for my 31" draw but maintains a great string angle with a total mass of 17oz  with all the changes I found every time I effected the string angle in a negetive way the performance drastically decreased ,I think with a beffed up lower limb via a power lam on a bamboo backed bow you could achieve similar results & play with the design to achieve perfect ballance, I would bet set would be low performance would be on the upper end for wood ,but the bow posted has no stack to 32" draw the draw is butter smooth out to my 31" draw for a 58" bow !

[Selfbowman]

I agree to disagree. I would love to see that design in a selfbow and its cast. You guys are to far ahead of me in the math for me to totally understand the whole string angle stuff. Yet in a selfbow I know my limitations in a reflexed bow to an extent. The wood in a selfbow will only go so far without set depending on the design. Longer limbs vs short limbs and on and on. I am only talking selfbows or even boo backed bows into account here. If the belly crushes we loose. Turning great bow into  a good bow. I think we might try some secret sauce on the heat treatment . Ok question? Has anyone ever heated a limb to say 350 degrees and brushed 140-160 degree hide glue onto the limbs and let cool the appropriate time for full cure? If so what was the affects. If I am so far off the intended post please be kind and say Arvin this one is not for you.  . Arvin

[Halfbow]

Stick Bender, yeah that design you posted includes many things that I would expect to make for excellent string angles, and an excellent bow. By having the limbs start out curved away from the string, they actually effectively get longer when you start bending them. That bow's limbs are pretty straight at full draw, which is great. That gets those tips especially far away from the handle.

You'd want to make it longer for a self bow, but the concept absolutely still applies and is possible. Because those tips only start out a few inches in front of the handle, it will strain the wood similarly to a long bow with a few inches of reflex. Make it as long as you'd need to for a long bow with a few inches of reflex, and you're good to make a self bow with a similar shape to the pictured bow. I'm actually working on a primitive materials bow that is an even more extreme design that uses some of the same principles.

[Selfbowman]

I agree to disagree. I would love to see that design in a selfbow and its cast. You guys are to far ahead of me in the math for me to totally understand the whole string angle stuff. Yet in a selfbow I know my limitations in a reflexed bow to an extent. The wood in a selfbow will only go so far without set depending on the design. Longer limbs vs short limbs and on and on. I am only talking selfbows or even boo backed bows into account here. If the belly crushes we loose. Turning great bow into  a good bow. I think we might try some secret sauce on the heat treatment . Ok question? Has anyone ever heated a limb to say 350 degrees and brushed 140-160 degree hide glue onto the limbs and let cool the appropriate time for full cure? If so what was the affects. If I am so far off the intended post please be kind and say Arvin this one is not for you.  . Arvin

Has anyone done this or are you all trying it before you comment??? Well I guess I better build a bow and try it. What is the best source for hide glue?
Arvin

[Stick Bender]

I havent used this glue for your purpose but its high quality hide glue very good stuff for sinew & so forth !

[sleek]

Knox gelatin at the grocery. It's the best. Tim Baker started a very similar experiment but lost interest. I'd like to see what you are able to do with it, especially if you build up a thin layer and leave it. You will need some matrix to hold it and keep it from crushing under compression.

[DC]

Slimbob is right this topic is really interesting to illustrate some of the advantages of the design I will post this bow granted its glass test bow but all the same principals apply & Im planing a similar design in sinew/horn composite with less aggressive bends but I have made 10 of these over the last year different riser/ handle lengths & different working limb lengths & many different power lam wedge tip combo's & and different amount of reflex and tested performance on all but this bow is short for my 31" draw but maintains a great string angle with a total mass of 17oz  with all the changes I found every time I effected the string angle in a negetive way the performance drastically decreased ,I think with a beffed up lower limb via a power lam on a bamboo backed bow you could achieve similar results & play with the design to achieve perfect ballance, I would bet set would be low performance would be on the upper end for wood ,but the bow posted has no stack to 32" draw the draw is butter smooth out to my 31" draw for a 58" bow !

I like this design although when I've thought about it my aim was to have it end up with straight limbs at full draw. That makes the limb lever longest as possible at FD.
String angle--- My gut says that string angle is probably a symptom, not necessarily a cause. You said that anything you did that affected the string angle in a negative way was a bad thing. Is that string angle at FD or through the whole draw? By negative you mean increasing the angle? What kind of things have you found that increase the angle?

[Selfbowman]

Sleek what is matrix??? My thinking is open the cells up and fill them with hide glue if it’s thin enough. Hoping  to make the belly more dance without adding much mass. I started one . How long for full cure on the glue. Guess it depends on the thickness. Arvin

[Halfbow]

DC, the bows you make with that design are great, and are a strong testament to how good the design can be. I think you're spot on, straight limbs at full draw is ideal. If your gut says string angle is just a symptom, I'm curious, does it have any feelings about what's the cause?

[Stick Bender]

Don yes I was talking FD/string angle ,a good example of negitive string angle is in Half bows reflexed bow drawing if you have length vs draw length ratio achieving good string angle is not much of a problem the trick is acheving it in short bows with long draw length, in shorter bows with long draw length it becomes a balancing act to still maintain good string angle in the pic there is another 58" bow compared to a osage self lever bow with slightly shimed forward leavers & a BBH thats approaching a neg angle all thought the more whiped BBH is a smooth shooting bow very user friendly the osage pic was under construction pic the tips where thined to the point of flexing and heat treated with 1/2 in forward ! Both natural bows are 68" !

[Selfbowman]

Ok stick bender which one wins the race. I am guessing the middle bow pic wins.

[Stick Bender]

Well it depends on what race as far as string angle there all acceptable the osage lever bow & the BBH are with in 2fps of each other the BBH has a better FDC the original 58" posted dwarfs them all both in FPS & FDC , I think for any given design & material there is a balance between working limb and string angle but for a 20 yard hunting bow Im comfortable with them all !  I will take user friendly over speed but try for both , I have bows that ring the bell at some crazy numbers but would not hunt with them, non user friendly ! Adam Korpowicz & Jack B Harrison have great exsplanation on this topic in there books !

[DC]

DC, the bows you make with that design are great, and are a strong testament to how good the design can be. I think you're spot on, straight limbs at full draw is ideal. If your gut says string angle is just a symptom, I'm curious, does it have any feelings about what's the cause?

Not really but possibly the actual lever length of the limb. A "lever" is the direct measurement from the fulcrum(grip) to the point of effort(where the string hits the bow) ignoring any bends. With a straight bow the lever gets shorter as the limb bends. Bad. With a reflexed bow the lever gets longer as the bow bends. Better but can be unstable and by the time you get the bow braced you've used up most of the bend. With an RD the deflex gives you your brace height without using up much bend and by moving the tips back it also stabilises the bow some so you can use more reflex. If you can arrange things so that the limb is straightest at FD then I think you would have maximised the lever length.
Also if you can move the the bend toward the grip you can shorten the actual string length. By that I mean the part of the string that isn't touching the bow. Then your braced lever length is short because the lever is measured to where the string hits the bow. This gives you a short lever when the bow is easy to pull and the lever lengthens as you draw it when it gets harder.
That was a lot of typing for a "not really" but those are my thoughts. I get the impression that some others here are swishing roughly the same thoughts around in their heads.
All that said if I understood the physics of bending a beam with a string maybe string angle would mean something

[sleek]

I really think you nailed it DC. The issue becomes stabilizing the limb from torque. That's where a wider limb comes to help, but with width comes mass, and the thinner limb is also the less efficient limb, so power in vs power our ratio starts dropping even though stored energy goes through the roof. That's the realm we play in.