My horn bow build-a-long

[bownarra]

Good on you for attempting a hornbow A 100 mile journey starts with a single step....
A bit of advice - you need to make the kasan eye bend less severe/greater radius and your tip bend could do with being tighter. A way to concentrate the tip bend and make sure it is exactly where you want it is to rasp out two curved 'scallops'  from the inside of the lathe, one on either side right where you want the tip bend to be. This method means that there is less wood to resist the compression during bending which equals less chance of raising a splinter on the outside of the bend.

[DC]

That was mentioned in Adam's book. What do you do with the "scallop" when you are shaping the back or do you leave the lath thick enough so that the bottom of the scallop is the finished thickness?
Also I got the impression that the radius of the kasan eye varied from war bow to flight bow. As no particular radius was mentioned I just assumed it was an individual choice. I will work on that after I take these trial laths off. A little heat should straighten them some. In order to end up with enough total reflex should I increase the amout of sal bend wgen I decrease the kasan eye bend?

[bownarra]

I make my lathes 40mm wide give or take. The scallops are around 25mm long and go into the width of the lathe by around 10mm each side. This leaves around 20mm width to play with when trying to get a straight core. The tip is only around 10mm wide when finished. This centre section is of course left full thickness, ideally 18mm. They are around half of the thickness.
If these cores you have already bent have knots in the them no matter how small they are no good for making a bow.
It is a while since I have rad the section in Adam's book on core shape but I seem to remember he does mention a radius as a starting point. It is easy on the first few bows to end up with a stiff kasan eye that doesn't flex quite enough. Also if the kasan eye is a tighter radius the bow will be quite a bit harder to stabilise and the sals will have a lot more stress on them so it is best to start a little 'relaxed'.
The difference between a flight and war bow is more how the limb tapers and thus where it bends. A war bows thinnest point will be right at the kasan eye causing quite a lot of bending there whereas the flight bows bend closer to the handle. Without getting too deep into the whys and wherefores the warbow is less stressed and able to be kept strung for long periods with little deteriation of performance due to the bend being spread over a longer bending limb. The flight bow however has quicker return speed of the limbs as the bend is predominately closer to the handle.
The sal should be straight and gradually blend into the kasan eye, the kasan is again straight (important) with the tighter tip bend aided by the scallops. Don't worry too much about totally reflex to begin with, as long as the tips are more or less 90 degs to the handle/sal section it will be good.

[DC]

Oh, the scallops are on the sides, I missed that, that makes sense. Thank you. My laths are about 35mm so I'll have to go lightly. The laths I have bent are just for testing methods and such. I will work them up to the point of  getting ready to glue on the horn and then I will trash them. They have quite a few knots. They would have made a nice selfbow though. I also thought that if I could bend the ones with knots then the good ones should be a cake walk.

[DC]

Here is my form by itself. If I round off the eye bend that will shorten or straighten the kasan. The Book says I should keep the kasan straight if I'm reading it right. Should I start from scratch.

[DC]

 I've taken the test limbs off the form and there was a fair bit of springback. I glued a piece on the sal end of the eye and rounded off the eye a bit. You can see the kasan eye bend is not so tight. Hope that's enough. I may make the tip bend a little sharper. I set it at 150° like The Book say but I may go to 140° to account for springback. It's also a lot easier to pull bend out than put more in. I didn't see any mention of springback in The Book. Maybe the longer soaking and drying would help. I should have waited but at least I'm working on something. I'm squaring up one of the test limbs pretending this is the real thing. I'll splice a scrap handle on it and see what happens.

[DC]

I managed to get registered to the ATARN forum but there's only one or two people on there. Maybe more will show up.

[DC]

My test limb and practice grip to sal "V"joint. I've never used hide glue for a joint, should the joint be a loose close fit or does it matter if you have to tap it home?

[bownarra]

The main criteria for the fit of the joint is that there is no light showing through once they are fitted together. It doesn't matter if the joint needs to be tapped home better that than too loose. The hide glue is perfect for gluing splices. Sizing parts well (with heat), apply thicker glue and push together. Let the glue gel properly. Then clamp lightly. I've done them with no clamps when the splices are perfect with no problems. Make sure and apply a fillet of extra glue once clamped.

[gorazd]

-close fit as possible
-make the joint area rough with saw blade (longitudial moves with saw blade for metal - small teeth)
-the joint area should be sized well with thin (hot) hide glue - at least 5 times. Let the thin glue penetrate wood properly and dry after each layer .... 10-15 minutes (gently heat with heat gun)
-Then make the glue thicker and put one thick layer of glue
-put the clamps on and tight well

My test limb and practice grip to sal "V"joint. I've never used hide glue for a joint, should the joint be a loose close fit or does it matter if you have to tap it home?

[DC]

I'm curious about something. You put on 5 or so coats of thin glue letting it dry between coats. Are you then depending on the thick wet coat to reactivate the dry coats? It just seems like a bit of redundancy. Why not put on a sizing coat and let it gel then immediately put on the thick wet coat. Wouldn't that accomplish the same thing without the waiting and maybe even better because you don't have to hope that all five layers get reactivated. I know this is the way it's done, I'm just wondering why.

[DC]

Here's the test bow glued up. I'm going to modify the form to put more angle in the tip kasan bend. I may try to put a little more bend it these with dry heat just to kill a little more time

[bownarra]

The reasoning behind letting the coats dry is so you cannot get a dry spot in the joint.
Applying glue, letting it gel then applying fresh glue would mean that the first just gelled layer could be removed (or part of it) when fitting the parts together. The dried layers of glue cannot 'come off'. All the layers do not need to be reactivated just the surface. This method of sizing with many coats of thin glue, drying inbetween and then applying the thicker final layer works perfectly.
Collagen glues contract as they dry and therefore wood to wood joints do not need high clamping pressure in fact it is counter productive. The key is close fitting, smooth surfaces to start with. Roughened surfaces trap air bubbles reducing glue saturation of the surface.
I like to test all these things for myself and it doesn't take long to glue up some test pieces. Try scraped smooth surfaces, 60 grit roughened surfaces, no sizing, thin glue, thick glue, clamps no clamps etc and then break them all. All in the name of experimentation and a bit of fun
It is well worth experimenting with the horn to core joint before going for the actual glue-up.
Yes you want to increase that angle in the tip bend or else the bow will stack early and not store as much energy as it could.

[DC]

I just noticed something(I can be a bit slow at times). With self or backed bows I avoid putting a splice in a bending area of the limb. The grip/sal splice extends well into the bending limb. Is this not an issue when the splice is sandwiched between the sinew and horn?

[DC]

Here it is at the end of today. Dry heat wouldn't cut it so I steamed the tip/sal bend to look much like I hope it will. There is a little reflex bend just at the end of the sal/grip splice on the left side. I'll have to watch for that kind of thing on the real one. No twist in this one. the centerline is nice and straight. Does this look more like what I should be trying for?