Trying to make a horn bow...it broke!

[Mesophilic]

This is my third attempt.  The fist was dismal.  The second is serviceable but cast isn't where I want it to be, probably because I didn't reflex it much when I applied the sinew and the core too thick making the sinew and horn layers very thin.

Third attempt came out highly reflexed.  But I can't put it on my tiller tree without it flopping off. I can't even attempt to bend it enough to get a string on it.  The siyahs and the reflex make it very awkward.  I don't want to start taking weight off of it until I see how the limbs are bending. 

So now what does a guy do?
(I know this will not be a work or art, just going for functional)

Before sinew:



After sinew:

[aznboi3644]

From watching most videos of horn bows the guys have jigs to bend each limb to help get it to brace. 

[stuckinthemud]

+1, they tie the limb to a curved block of wood (can't remember the name of it) to pre-shape the limbs - I think just stringing the thing might be a bad idea

[Mesophilic]

Thanks,  guys.  I found some videos and images of jigs and the preshapes I think one person called "tepelik".

[bownarra]

Yes teplics are used but if you have a discrepancy in your taper you can easily break the core using them. Again they have to be just the right shape for your particular bow. They aren't used to shape the limb that is all done prior to tillering by making darn sure your tapers are good. If you have a weak spot on a limb and then try to bend it over a teplics you will break the core.
Personally because I know my tapers are good I go straight to a pegboard for initial stringing.
Be very careful about getting the teplics right. Unfortunately no-one can tell you what is right for that bow.
When you make the handle/fade area make sure you have a smooth curve going from the limb in to the handle. I can't tell from the pictures but it looks like you have butt jointed the end of the horn strip up against the riser? If so that is a bad idea! It will delam there. The horn should go all the way up the fades. Like most glass bows are made.

[Mesophilic]

Thanks for the tips Bownarra. 

I'll admit that I feel like I have a child's understanding of how all this works, but a guy has to start somewhere.

The horn does go up the fades but during glue up the cracked when I clamped it, right at rhe bottom of rhe fades,  I think because the transition was too abrupt. I used G Flex epoxy and made sure I had enough to ooze and fill any gaps and it did ooze out of the cracks so maybe that helps.  The core tapers about an inch forward of the fades and I'm going to do the same with the horn to take some stress off of the areas where the crackkng occured and move the working portions of the limbs forward a bit.  Don't know if this will work, but the only other option is to reclaim the sinew and start over...which I figure I can do if the bow fails anyway so might as well experiment.  I've already resigned myself to the fact that the bow won't survive but I've learned at least a few things during this process.

The cores are hickory as it's the only wood that I've found that can hold up to how dry it is here, all other woods I've used with sinew, including osage and bamboo, get riped apart by the drying sinew. 

I made some crude tepeliks yesterday and so far so good.  Need to reduce some draw weight, my target is 50 pounds at 28 inches but in exercising the limbs it feels way more.

[gorazd]

You can make tepelics with smaller radius of curvature

[Mesophilic]

Well it broke. 

Didn't suprise me.  I think I learned something important as I put the puzzle together on how to make bows at high elevation with low humidity.

When I put on a second course of sinew, I don't think I thightened up my reverse string enough.  When the sinew reflexes the limb here as it dries, it will literally pull the wood off the back of the bow as it dries.  The first course went on just fine.  But the second course lifted a large sliver on the limb that broke.  I went ahead and filled with epoxy and clamped it back down.  I've never had this problem at other locations I've lived.

The fracture point is right where that sliver lifted.  In the second pic,

I ripped off the sinew and you can see the chunk of wood still stuck to it.  The arrow points to right where the original fracture is.

[bownarra]

That is a shame. Really sorry that it broke.
What poundage/drawlength bow are you looking for?
Yes tightening the reverse string after gelling but before any drying takes place will help.
What strength glue are you using? Did you make it yourself or is it bought?
I have the opposite problem to you...high humidity almost constantly.

[bownarra]

Having another look I suspect the sinew wasn't stuck properly. There should be bits of 'fluffy' sinew still stuck to the limb, it looks very 'clean' around the break.

[Mesophilic]

It is homemade hide glue made from rawhide scraps.

I'm going to order some dried hide glue for the next one, so I can use rhe percentages you suggested.

Here's another angle on the fracture.

[bownarra]

 You are best using glue you have made yourself. That way you can guarantee the best strength. The very best glues are made by making certain that the temperature never exceeds 60 degs during cooking of the rawhide/sinew etc and it is heated for no more than 8 - 10 hours.
If it gels strongly it is more than likely strong enough.
You can dry your fresh glue by letting it gel in thin layers and cutting into small pieces. Place the pieces in front of a fan in a cool place and it will dry in a day or so.
I know you mentioned the drying crack as the likely cause but even when a core is broken right through a good sinew layer will keep it together. I once had a Turkish bow at full draw for the first time....heard the dreaded 'tick'. I checked the bow all over but couldn't find anything wrong initially. It was only later that I tapped the sinew and found a bit that wasn't stuck. That limb kept acting weak and eventually I gave up on it soaked it in the bath for a few weeks! This revealed that the sinew had delaminated from the core, the core then broke because it was now feeling tension. The point being that even with a core that was broken clean across the back the bow could still be taken to full draw because the sinew layer as a whole was ok. I suspect I got a contaminant on the core somehow that caused the delam. It was a real pain because that bow was basically tillered, perfectly straight and right on desired poundage all I did was open it up and string it.....that will probably never happen again!

[sieddy]

Man I can't imagine how frustrating that feels after so much careful work--it's bad enough when a self bow fails!
Oh well back to it- it'll be worth all the pain when you start making the fully functional beauties! 😊

[Mesophilic]

Man I can't imagine how frustrating that feels after so much careful work--it's bad enough when a self bow fails!
Oh well back to it- it'll be worth all the pain when you start making the fully functional beauties! 😊

Thanks!  Though I'd settle for a "function ugly duckling" right now.

It's kind of like going back to when you made your first selfbow, and you read tons of books, scoured the internet,  watched videos, felt in over your head when the wood shavings started falling...but x's 100 

[simk]

Hello Mesophilic

How much sinew did you put on it? For me that layer looks quite thin.

I'm also about to do my first hornbow (-attempt), which will most likely also fail  . Soon its time to bend it in...makes me nightmares already 

But one day....one day....

Cheers