Question for horn bellied bow builders

[colin1991]

Ok, for starters, look at the amount of reflex in the limbs of a Turkish bow... You are bending the limbs almost through 90 degrees even before the bow is drawn... I'm talking about using 1-2 inches at either end to create a small curve.

Second, the glue I will be using has never failed on me and I have bows up to 150lbs which are held together using it. It is a structural grade epoxy for use in buildings, joining beams.

As for horn,compressing 8 tines further than wood, are you talking about compressive stress or compressive strain, because there is a massive difference between the 2. I'm aware horn has a massive crushing strength, because of its density and hardness but if it could physically compress 8 times more than wood it would not be any good for a bow because it wouldn't hold any weight.

[bubby]

Well sounds like you got it all figured out😕 good luck

[mikekeswick]

Yes indeed look at the reflex on a Turkish bow....where is it? I've made a few and have experienced the problems/heartache through thinking I could just do it how I wanted.
I could save you a lot of problems but as Bubby says looks like you already know what you are going to do! Good luck to ya!

[colin1991]

Is there any curve in the limbs forward away from the direction the Turkish bow is draw when it is un braced, yes. Therefore it has reflex in the limbs. Just looking at photos of your most recent build un braced id say the limbs are reflexed heavily and also recurved slightly at the tips...

No need to say things I want to try WONT work when you have not given any reason as to why... For example, why won't Mass work as a core? Its very strong in shear and bending and wont fail in my design. It will also allow for some pre tillering before I add the horn layer to the belly.

[loon]

Most (but not all) of the reflex in horn bows is at the kasan eye, tip, and sometimes grip. Turkish bows usually don't have any reflex on the bending limb (except on the kasan eye?) unless they're flight bows? Well, war bows don't.

Massaranduba might work, but if it's an oily wood there's a chance of delamination and you might have to treat it somehow

[mikekeswick]

Nope the sals were straight before adding sinew. Any reflex in the bending limbs is due to he sinew drying. The reflex at the kasan eye is a different matter altogether. That was steam bent in to the core. Indeed when tillering these bows the most likely place for delamination is at the reflexed kasan eye.If you have too much reflex in the sals the forces acting on the gluelines are literally prising the layers apart compared to if you start with a straight limb then the forces actually press the layers together. You can make reflexed bending limbs (still minimal) as per flight bows but not for your first try!
The limb profile for your prod would be best with straight limbs through the center section and recurved tips. Stress the composite construction enough by drawing it further than wood alone/make it shorter but don't try adding crazy reflex through the bending portions.
Maple has the required charteristics for a core massa doesn't....its too dense for a start and won't accept glue as well as maple. Maple has been used for cores for an awfully long time on all sorts of bows. Any core on any bow doesn't benefit from being dense. The core has nothing to do with draw weight either it simply puts the back and belly surfaces the required distance apart for the required draw weight.
Any core you use will have to be shaped but it's best done after the horn has been glued.
Also you haven't mentioned sinew - you must use sinew for the back! Forget wood.....
Horn is a lot less stiff than most belly woods. It has less bending resistance but its elastic limit allows it to be bent 8 times further than wood. Marry this to the fact that sinew also has low stretch resistance but the ability to stretch 8 times further than wood = perfect combo.
I went to uni to study mechanical engineering and am well aware of the differences between stress/strain....it was one of the first topics.
Don't try to reinvent the wheel - use the lessons that can be learnt from the old bows made by the real masters.
Good luck with your project.

[colin1991]

You now say that there is in fact reflex in the bow... doesn't matter how the reflex gets into the bow, its there! Your bow has picked up reflex due to the sinew shortening when it dries (im assuming that's what happens, never used it so I don't know) which leaves the horn in tension... im putting reflex into mine using a form, also putting the belly into tension.

I'm very aware of what the core does in a bow and second moment of inertia. I make a lot of heavy draw weight tri-lam English warbows and have found that denser core timbers help to retain glued reflex.

As far as horn being less stiff than belly woods, I'd have to do a small bend test to compare them since I've never used it in bending., However, its potential for strain in bending is not what im looking for for this project.  The radius of curvature along the length of my prod will be much greater than that of the limb of a turkish bow for example.  I want horn for its compressive crushing strength rather than bendability.

I have found a source of sinew so I will be doubling my order or horn (if I can actually get it) and making 2 prods.  One using a sinew back and maple core as you have suggested and one as an experiment with a hickory or bamboo back, JUST to see what happens with it.

I have a degree in Civil Engineering so Im very familiar with things bending and how they work, and I wanted to try something different and see what happens.  We learn more through failure than success, hence my experiment.

Colin

[bubby]

Well I'm not sure why you are asking for advice and then arguing with it, there is not much in common with a english warbow and a hornbow, the best approach to building bows is to be a sponge and absorb the advice given and wring out the good from the bad.

[scp]

As a guy who just makes selfbows with less than perfect staves readily available but still wants to make a bow that shoots a 10 GPP arrow over 180 FPS, I'm learning a lot from this thread. I also would like to experiment with a bamboo backed horn bellied bow. It is possible that horn alone would not be helpful without sinew on the back. But it is also possible that a special design can use horn in the belly to improve the speed of a bow. As Collin1991 suggested, a highly reflexed bow with horn belly might work, especially if the bamboo back is wide enough while the horn belly is rather narrow and thick.

[Urufu_Shinjiro]

Just remember there is a fine line between innovation and reinventing the wheel...

[loefflerchuck]

Your research needs to go into the french crossbows of the middle ages. They were laminated sections of horn put together like the bamboo or wood of old Yumi bows and with a thick sinew backing. These are after-all primitive crossbows and were used with devastating effect. They were Richard the Lionheart's favored weapon for his army in his conquests.