Ozbow

I've been looking at this bow for awhile and wanting to have a crack at replicating it. The bow is 36" tip to tip with a horn belly, 1/8" thick osage core and sinew back, pulls 42# @ 23"
My choice of materials as stated will be a 0.40" Gordons fibreglass strip on the belly as a substitute for the horn, a 1/8" thick hickory core and several layers of sinew for the backing. I'll be reflexing the hickory core as much as possible before applying the sinew and glass to really get that sinew stretching and glass compressing

What would the best method for reflexing hickory be?

Cheers genteman
Cameron

Cameron, because the hickory is so thin it may be best to make a form and glue the fibreglass and hickory into reflex.

Some reflex will come out but you can regain the reflex by pulling the tips closer together with some string. Have a look at videos of making Korean bows.

Pull in extra reflex if you want to and then apply the sinew.

Daryl.

I would be inclined to lay the sinew onto the hickory with a reverse braced string and allow it to shrink and pull into reflex then add the glass or horn. Maybe try to source some Buff horn off ebay and make it authentic rather than use glass. Cheers Steve

longbow steve wrote:I would be inclined to lay the sinew onto the hickory with a reverse braced string and allow it to shrink and pull into reflex......

Steve,

With the hickory core being 1/8" thick maintaining symmetrical reflex could be an issue. I don't have any ideas on how to maintain the correct shape.

With all the horn and sinew bow making videos I have watched the sinew is applied last.

Daryl.

That little bow is a near replica of the very short Plains style Indian horse bows which were bellied with Dall or other Mountain sheep horn and backed entirely with Sinew. There was no core material that I am aware of. According to Jim Hamm (Native American Bows and Arrows) and Laubman's (American Indian Archery), the laying on of the sinew is all that is required to induce huge amounts of reflex. The greater the thickness of sinew, the greater the reflex because of shrinkage during drying. That is a common principle and has references to it in Paul Klopsteg's book (Turkish Archery).

Your problems will simply be adhesion to the fibreglass surface and twisting during drying. Finding a glue which will adhere both to the glass and the sinew will be a problem and my suggestion would be to put a skin of wood over the glass when flat using a synthetic glue and then glue the sinew to that wood skin with an animal glue. Sinew layers are applied in layers up until the desired amount of recurve or draw weight is achieved.

Tillering is accomplished by strategically thinning the sinew thickness rather than the belly as is conventionally done on wood bows for obvious reasons of lack of material thickness from which to shave.

Before applying the sinew, you could place a well-feathered block on the back side of the glass and lay the sinew over it to form some kind of handle. although the Plains Indians seemed not to bother with this in the pictures in the books cited above and as your picture shows.

They were highly sought after among the Plains Indians and were very very expensive bows to them.

Good luck on the venture.

As an afterthought, even though I have never made one myself, I would be inclinded to glue the sinew onto the glass with it still very wide for its full length as an aid against twisting. Once it is glued and drying begins, you will have to keep a close eye on it according to the books above to ensure that it retains tip alignment. When dry, and fully recurved to the point where it is not increasing, you could then cut it out to preferred dimensions.

If I had some of the pictures of Plains bows handy, I could have uploaded them for you to have a look at. I will have a ferret around for some, but there will probably be plenty on the web anyway.

Here she is at her current state of progress. I steamed the hickory and clamped it to a form with 4" of reflex and left it overnight, the 'stave' maintained 3" of reflex which I was quite happy with so I went about gluing the fibreglass to the belly using techniglue.

The stave developed a bit of twist but it's nothing I can't live with, time to start processing some sinew

cmoore,

With a core of that thickness and a bow of that length, don't be surprised if when backed, you can't get the beggar to bend at all. If you put a reasonable amount of sinew on the back sufficient to maintain the 3 inches of reflex or even increase it slightly, don't be surprised if it comes out well above 60 - 70lbs.

The propeller looks to be in the outer part of the blank, so it will be gone when you put the side tapers into it. Otherwise make the side indicated by the red arrow a bit thinner by chamfering the glass on the belly as well as the thickness of the sinew layer on that side. This is going to be a very interesting build-along.

Cheers dennis .. im not yet sure as to if I'll sinew up the blank at it's full width or cut the tapers and then lay the sinew? Which brings me to another conundrum, given that the bow is already in a reflexed state and I'm no longer reliant on the shrinking of the sinew to pull the bow into reflex, could I glue the sinew down with a non hide based glue, say titebond II? As Ed Scott (bowyer) does?

cmoore,

I really cannot advise you on glue types other than that in my few books on the matter, all use animal origin glues. On would have to know with synthetic adhesives whether or not the chemical compounds do not react adversely with the sinew and I do not know how to assess that other than by actual use.

At any rate, you can just glue some sinew onto a bit of the same wood and see what happens to it before you commit to using it on the bow.

However, these same sources apply the sinew with the bow in pretty much the finished shape. All also agree that the sinew will definitely pull the bow in increasingly greater reflex based upon the thickness, drying time allowed and ambient humidity.

Expect the bow to increase reflex in arid areas and the reverse. The reflex it now has is not the final shape of your bow unless you leave it very thin indeed.

Okay I've got some strange results to report.
Since the application of the sinew which was soaked in warm water then glued with titebondII the twist in the limbs is now on the opposite side, and whats more is that the belly has now gone concave through the 'handle' section of the bow
The bow has also lost an inch of reflex ... though im putting this down to the wood absorbing the water from the sinew and softening up. I'll let the glue cure for another day or so then carve out some nocks and put her on the tiller with the long string.....I've got mixed feelings about how this one's going to end up

cmoore wrote:Okay I've got some strange results to report......I've got mixed feelings about how this one's going to end up.......

Did you use any types of forms to hold the components rigid whilst the glues/epoxies were curing?

Daryl.

greybeard wrote: Did you use any types of forms to hold the components rigid whilst the glues/epoxies were curing?

I made a basic form and then steamed the hickory and clamped it to the form leaving it over night. I then glued the glass to the belly and clamped it all back in the form again leaving it overnight. But whilst the sinew was drying it was not clamped down in any way hence that migrating twist the handle section ending up concave is a real noodle scratcher

cmoore,

That concavity at the handle section shows how strong the sinew is. This is going to be a very interesting project indeed. 'Mixed feeling' would barely describe it, but I think both Daryl and I would suggest that you continue on to the either bitter or gratifying end just the same. If you stop now, you won't learn anything.

My suggestion now would be to scrape the centre of the sinew down just a little at at time in that area leaving it thicker at the sides. The concavity in the middle is telling you that the tension side of the bow is pulling more than the edges. If the edges were too strong, then the belly would be convexing.

In my old books, the old sinew bowyers held their bows in a system of clamps intended to prevent the bow twisting or bending laterally, but I cannot find anything about the phenomenon you have experienced. Just the same, my bowmaker's intuition tells me that the suggestion above is what I would do if I were on that job. See what Daryl thinks as well. He has much more experience with short curvy bows than I have.

I would leave that bow for a week or two, rather than a couple of days. While the TBIII might cure in 24 hours, water-soaked sinew will still be wet within the glue for quite some time. It will cost nothing to wait a little longer, and could cost dearly to rush to finish the project.

You may find some of the reflex comes back as the water inside the sinew slowly leaves through the glue. Hopefully.

The anticlastic curvature imparted post-sinewing is called the poisson-effect. It is the beam's attempt to maintain dimensional stability under flexion in one plane by also flexing in the other. This is a rather extreme example of it, but it happens to all bent beams to some extent. Flat ones anyway.

Cameron, I think the thinness of the strip of hickory and its grain orientation is part of the problem. Dry heat applied in the correct spots and gentle twisting of the limbs may correct this problem.

Check out the on line videos of Korean bowyers correcting limb twist in their horn and sinew static tip bows.

Another approach in making these styles of bow could be laying up the sinew in the form and making a strip of sinew that can be glued to the core and glass.

Cover the form with a plastic film that will act as a release agent, lay up the sinew, cover with plastic film, place a pressure strip on top and clamp in place.

When the glue has dried the sinew matrix can be glued in place like a lamination.

Daryl.

The last time I used Sinew on a Bow I glued it on with Bondcrete and glued it onto a fully Tillered Stave. I may as well of Backed the Bow with Canvas or Rawhide as you need the Collegon in the Animal based Glues to activate [ for want of a better description ] the Sinew's Properties. Purely from a effort/time perspective the amount of effort put into harvesting/ preparation and application of the Sinew my experience suggested I would have been better off just using Rawhide as not using Animal Glue robbed the Bow of any performance gains. It was a tough as nails backing and looked way Cool.

I think you should have Tapered/Tillered the Bow before applying the Sinew and then retillered when the Sinew was dry. I reckon the Core should have tapered in thickness also . If the Limbs where tapered down their length I doubt you would have had twisting issues to this extent. I would also have left it in the Form until it was judged Dry because as more moisture evaporates tensions will shift further. I do like a challenge though and chasing a Propellor Twist can be as vexing a challenge as there is in Bow Making. I'd guess it will take as long as 3 weeks for the Backing to be Cured, that's how long I judged it took the Sinew/ Bondcrete Bow to dry thoughly. I guess when you do begin Tillering you will have to remove material from all surfaces of the Bow. Based on my experience with Bondcrete and Sinew I doubt the Sinew would set as hard as when an Animal Based Glue is used and it will go a bit "Furry" if you Sand it.

I have a Grozer Biocomposite, Horn Belly, Timber Core then what appears to be a very fine Fibreglass Lamination but it could be the undisclosed Glue Mr Grozer uses and a Sinew Backing that was made in the manor Greybeard suggested with the same undisclosed Glue. It is most certainly not a PVA type Carpentry Glue. Very Impressive Bow, I'm not the only one who wants to know what type of Glue Grozer uses with his Sinew Lamination. An interesting comparision in that Grozer Glues and Binds Siyahs onto the Body of the Bow which resembles you partially completed Bow

A really interesting Project, I'm sure this will shoot an Arrow, I look forward to watching your Progress cmoore

regards Jacko

I agree with you there jacko, the core should definitely have a thickness taper prior to the application of sinew. I braced the bow today and wasn't suprised by the twisted mess that confronted me Im thinking that rather than sanding off material to attain tiller I'll add sinew to the weaker areas of the bow to even out that twist
That's a very interesting idea to Daryl, I never thought of anything like that before. As an after thought though isn't there any modern day material that would be equivalent to sinew?

cmoore wrote:.........That's a very interesting idea to Daryl, I never thought of anything like that before. As an after thought though isn't there any modern day material that would be equivalent to sinew?

Synthetic materials such as glass yarn and carbon tow definately have the strength but lack the elasticity of sinew.

http://www.fibermaxcomposites.com/shop/ ... fiber.html

Daryl.