My horn bow build-a-long

[bownarra]

Yes make sure the sinew is even. If you have different amounts on the limbs it will season funny.

[DC]

OK. now how about the sinew wrapping around to the belly. I found this to be the most difficult part of sinewing. In the tillering section Adam says

The scraping of the belly or the sides of the bow is done in such a way that the roundness of belly is always maintained. There is no need to worry about exposing the wood of the core at the edges of limbs, but the belly should still remain round with the sinew layer kept as the widest surface on the back of the limb.

Karpowicz, Adam. Ottoman Turkish bows, manufacture and design: second edition . Adam Karpowicz. Kindle Edition.

If there is no reason to worry about exposing the core, why do we bother wrapping the sinew around the sides?

[bownarra]

You can remove the belly sinew when tillering. You can then add the belly sinew once the bow is tillered. Personally I think as long as there is sinew on the edges you are good. You will have the devils own job trying to get it to stick to the horn belly and stay stuck anyway.

[sleek]

You can remove the belly sinew when tillering. You can then add the belly sinew once the bow is tillered. Personally I think as long as there is sinew on the edges you are good. You will have the devils own job trying to get it to stick to the horn belly and stay stuck anyway.

Hide glue doesn't hold well to horn?

[bownarra]

Are all applications the same?

[sleek]

Are all applications the same?

I'm sorry, I dont understand.

[bownarra]

To glue horn effectively with hide glue first you must make the surface smooth. Then size it with 5% glue around 20 times in warm conditions. Then heat it to 40 degs and glue with 30 - 35% glue whilst everything is hot. Solid clamping is a necessity.
Now try and do all this on a horn belly that is already glued up into a bow.....don't get me wrong it is possible but personally I've found it not worth the bother. The sinew is in compression and tends to lift off the belly. Also when tillering unless you are super lucky and the bow doesn't need any tillering you end up removing it anyway. As long as the sinew is the correct thickness on the sides and is blended into the curve of the belly I haven't had any problems with no belly sinew. 

[DC]

So if this bow turns out to be ,say, 55#. 10# too heavy. If I only have 1/8" of horn(possibly less because of the grooves) will I be able to get it down to 45# by scraping the horn or will I have to narrow the sal/eye? If the horn gets too thin will it buckle? How thin is too thin?

[bownarra]

How long is a piece of string
If you followed those dimensions I gave earlier for the 45#'er you will be ok.
2mm is about the mimimum for horn thickness.

[DC]

Getting close to time and now I'm starting to have doubts. I had to remove quite a bit of sinew to even it out. Is it too late to add one layer of full length sinew? Would it stick well?

[stuckinthemud]

I have only sinewed 1 bow so I am no expert but I think you can apply a new layer of sinew at any time as long as you do everything properly.  My question is whether you need to apply any more - if the calipers show the thickness is correct then aren't you best leaving well alone?

[bownarra]

This is why you need to weigh, very accurately, the sinew bundles. Make absolutely sure they are the same for both limbs. Apply them evenly and you won't have problems with too much ,too little etc...
Another very important part is to make sure there is the same amount on either edge of the limbs. If not then the bow will twist as it's drawn and you won't be able to get a straight bow out of it.
The last layer of sinew must not have 'violations' where you removed some. The last layer absolutely must be one whole layer. I know you can get away with it on wooden bows but not hornbows, the ends will lift, maybe not straight away but over time they will lift.
When I've taught friends to make hornbows I tell them from the very start do not expect your first attempt to be a fantastic shooter....even with somebody on your shoulder it is all too easy to make a mistake! It's a journey learning to make hornbows and the beginning can be frustrating! There is no magic to it BUT it can take a while for all the subtleties to sink in and realise how important ever single step is
Anyway good luck and don't stress about it!

[DC]

But is there any problem applying another layer now?

[bownarra]

File/sand everything down to perfectly even thickness both limbs. Do the finishing work to almost final thickness with 60 grit paper, then finish off with 80/120grit and the freshly exposed sinew will stick properly.
Make sure to size with either very thin 5% glue or hot water just before laying down the new stuff. Also where you are working should be hot to avoid any adhesion problems.

[DC]

Thanks. It's going to have to wait a couple of weeks to get the shop warm.