Jack Farrell's Subeixi Bow Reconstruction

jack farrell · Post by **jack farrell** » Fri Sep 10, 2010 12:21 am

This bow cannot be tested as it. The stability problem is mid limb. When strung it is possible to bend the tip any amount in either direction, till the string comes off. Upon drawing it will accommodate by itself.

Is it insanity to think that a flat could be rasped onto the edge of each side and the core widened slightly? This seems to be in the spirit of the originals.

Before adjusting, the bow turned at 22" and #65.-j-

Adam Karpowicz · Post by **Adam Karpowicz** » Fri Sep 10, 2010 9:55 am

Yes - the instability mid limb, where the limbs narrow. You are right, the edges were formed into a little bit of a ridge, which tends to diminish at the deflex section. The instability will be less when the limbs are wrapped two times with sinew so the threads cross. I believe the wraps should be well dried for at least a month.

65lb at 22" will be around 120lb at 28". Even in the heat and humidity of Texas! Very close (prob. a little heavier) to the bow I made .

Adam

jack farrell · Post by **jack farrell** » Mon Mar 14, 2011 12:49 am

Well folks half a year has passed and I have taken a different tack to salvage my Scythian bow. I was going to take off the backing and reduce the core but instead I band sawed off the horn belly and took about 40% of the core along with it. Because the bow was so stiff and unstable, this seems like a good solution. I have replaced the thin horn with a thicker one, about 1/4" or maybe a little more. This will allow for tillering without threatening the structure. To do this the spiral sinewing was removed on the limbs but the hooks and grip were untouched. The new belly strips were butted into the widened part of the grip and tapered out below the hooks as original.

So in dimensions the bow is the same as the original except for being slightly thinner. This should give a stabler cross section.

Both belly slats were cut from inner curve of Nubian Ibex.

Some other thoughts on making a Scythian type from a single Ibex horn; After removing the knobs,the first cut would be to remove the outer curve slat but stopping before getting to the tip.

The second cut would remove the inner curve also ending before the horn tip.

Then the two side slats would be separated leaving the entire original tip on one side strip and the fourth side strip would also have a thick but shorter tip.

As they are cut one would have the ingredients of an asymmetric Scythian bow; one long outside curve belly slat, one very long side slat for the upper vertical limb slat, another shorter inside curve belly slat and a shorter sidewall slat for the lower vertical core slat.

Adam, Considering the core and sinew drying time already elapsed, how long should I wait for the new belly to cure?

Adam Karpowicz · Post by **Adam Karpowicz** » Mon Mar 14, 2011 10:30 am

Jack

The sequence sounds very probable and it would be very efficient. Then one horn = one bow. It is quite possible they used other scraps of horn for the bellies as well. Since you you have experience with ibex, perhaps you could do a few mechanical tests, such as bending tests for the modulus, and compare with buff horn? I do not expect anything dramatic, but it can be interesting and helpful for the replicas. Not the Siberan or Persian ibex, but still a different species.

I usually wait for a month for glue joints to dry. Perhaps you may want to consider thinning, or better narrowing the outer limbs and tips, so that the bow gains in cast and be more in proportions to the original? It could be done after tillering.

Adam

jiao · Post by **jiao** » Mon Mar 14, 2011 4:29 pm

adam:
bending tests for the modulus

i think you are said the very important thing share to us, thanks !
maybe many test (bending and others) follow each step , if you bend it it is break or not fine, you has time redo it and think a few or more glue or weak glue,at least you need made other one bow for test

jack farrell · Post by **jack farrell** » Mon Mar 14, 2011 8:27 pm

Adam; How would I perform a mechanical test for modulus? I have scraps of various horns and two kinds of Ibex.

Using my cutting method, the greater part of each sidewall would remain but of shorter length.

I am taking my bow to the Silk Road Symposium in Philadelphia this weekend but do not know if any archers are in attendance. But carrying a Scythian bow around should ferret them out if there are!

Adam Karpowicz · Post by **Adam Karpowicz** » Tue Mar 15, 2011 11:26 am

I meant a standard bending test used in industry for testing lumber. Basically, the pieces must be exactly the same in all dimensions down to a fraction of mm, supported by the ends and weighed down in the middle by a known weight. The deflection is measured by a caliper and the modulus in bending is calculated from a formula. It is better to have several samples of each kind for a more meaningful average. I tested horn like that before.

The test can give a rough idea about the stiffness of horn within, realistically, say 20%. It is more than enough for our purposes, because in the laminated construction one layer contributes only a fraction to the overal stiffness of limbs and therefore to the draw weight of the bow. Even if the stiffness (resistance to bending, not the resilience) of one horn is twice as much than the other, the bow will be only perhaps 15% heavier.

The resilience, or hysteresis, can be tested by Dick Baugh method, which is a modified Tim Baker bending test if I recall. I have not done that, but it is not too difficult.

The properties of the horn, however, depend heavily on its moisture content. The sample must be kept together to equilibrate for a long time and the tests done in the same room.

Adam

jack farrell · Post by **jack farrell** » Tue Mar 15, 2011 12:30 pm

The age of the animals, the age of the samples, the health of the animals, the place on the horn, the orientation of the grain, etc, etc.

JJ · Post by JJ » Tue Mar 15, 2011 7:01 pm

Last not least, temperature is important, too ...

I have the impression that the strength of horn can be variable inside the species. It will be probably depend also on the shape, e. g more or less curve in the horn.

So, comparing horn can be difficult...

JJ

jack farrell · Post by **jack farrell** » Tue Apr 19, 2011 1:19 am

Do you guys notice how I keep resurrecting my thread? Like my Subeixi bow, back from the brink of death!

All those contrivances described above have borne fruit. My beloved bow is up and shooting; stable, flexible, manageable. Right now I have drawn it to 26" but it is not stacking.

You can see the new belly and how it was spliced in. There is no wrapping yet, it was left off for tillering. The upper top limb needed warming and flattening as Adam described so long ago. This was done with the heating pad and a former made for the backing side. Later left strung overnight, relaxed and braced several times, then braced and shot.

You can see that the grip and hooks are not out of proportion.

redhawk · Post by **redhawk** » Tue Apr 19, 2011 6:17 am

Jack, great repairing job, looks quite good. The tips are looking a bit twisted, maybe it?s the angle of the pic?
Never give up a bow, until it has broken.
Michael

Dusan · Post by **Dusan** » Tue Apr 19, 2011 6:22 am

Good job , Jack !

daryush · Post by **daryush** » Tue Apr 19, 2011 7:53 am

Wow, looks amazing!

Kyudohund · Post by **Kyudohund** » Tue Apr 19, 2011 9:36 am

Congratulation Jack! Very fine work!

Zoran Pavlovic · Post by **Zoran Pavlovic** » Wed Apr 20, 2011 12:39 pm

Can't wait to see first shoot. Amazing!