Sinew Backed, Double Curve Bow

[JackCrafty]

This is my first build-a-long.....and my hope is that it will spark a discussion on how to produce a replica plains bow with the best possible performance.

The wood I will be using is juniper....not because juniper is awesome.....but because it is what I have available right now.  The wood has already been chosen, cut down, shaped, and seasoned.  What's left is the application of sinew, making a bowstring, final tillering, painting, finishing, and shooting to test performance.

Many of you guys have already built double curve bows and it seems a lot of people have one.  The one thing missing, though, is how to get one to perform well without turning it into a wide-limbed, narrow tipped, long, non-bendy handle, laminated monstrosity with an arrow shelf cut in the side (yuck) and fast-flight string.  I've looked high and low and there are few references on how to build a reproduction of one of these.....far fewer than the databases on how to build a traditional ELB, for example.

Ok, enough introduction, the first step is choosing the right wood.  The wood must, first and foremost, be very flexible.  The MOE and Work to Maximum Load (WML) must be higher than average....with ash wood being the average.  It must be easy to bend with heat and or steam.  It must have been available to NA's.  And the wood has to be able to withstand the strain imposed by the dimensions of the originals.

Since I am using juniper, I will discuss how I choose a juniper stave.  The pictures show that not all juniper is created equal.  The ratio of sapwood to heartwood varies quite a bit between trees and between branches and trunks of the same tree.  As a general rule, tension wood (the upper side of limbs or leaning trunks) has a very high percentage of heartwood...and is the best choice for bows...if you can get a long enough piece without twist or branches.  However, juniper trees growing close to water seem to have a lot of heartwood in their trunks (which are usually straighter than limbs) and this is the wood I try to harvest.  I have made bows with all heartwood and all sapwood and they both work well.....but the heartwood is better at not absorbing moisture and taking set.  The bow in this build-a-long is almost 100% heartwood.








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[JackCrafty]

The measurements for this bow will be very closely matched to a bow I've already built out of juniper (with the same amount of heartwood).

The older bow's mass is 10.9 oz.  The accompanying string is .4 oz.  The new bow's mass is 12.9 oz.

The width of the older bow is 1-1/16" and the new one is 1-5/16' wide (I plan on making it stronger than the older bow).

The thickness of the older bow is 1-3/16" (including sinew) and the new bow is 13/16".

The limbs of both bows are tapered gradually to the tips in both width and thickness (just like the originals).

The new bow will have slightly recurved tips.



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[benjamin]

is that the normal brace height on the older bow? does it slap your thumb? Very nice. Can't wait to see the rest of the build along.

[sailordad]

i was curious too, however if you look at the left limb you can see the string is off the nock, atleat i hope it is cause thas gonna hurt other wise

[JackCrafty]

The overall length of the older bow is 47-1/2" and the new bow is 49-1/4" long.  The extra length is for the "tassel pin" at the top of the bow.

I'm also posting a couple pics of how I measure the "curves".  The shape was mainly done by eye and then fine tuned with a tape measure.  The general shape is something that I learned with practice (with juniper in this case).  Other wood types will have slightly different curves depending on how much set I expect to have in the final bow.

The central curve is 1-1/8" from from the edge of the board to the back of the bow.  The distance between mid-limb curves is 24".  The distance from the edge of the board to the back of the bow @ tips is 1" (not shown).

(That's it for now...I'll post more soon).

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[JackCrafty]

Yes, the older bow is unbraced in the pics.  The normal brace height is 4-1/2".  Sorry for the blurry pics....I plan to replace my cheapo camera in a week or so.

More pics of the older bow can be seen here:
http://www.primitivearcher.com/smf/index.php/topic,9026.0.html

[JackCrafty]

Just so we are all on the same page...here are some pics of the real things...



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[a finnish native]

nice thread. Remember that you only have to reflex the bow in the handle. no deflexing the outer limbs is necessary. that will happen automatically with set and tillering.

[JackCrafty]

Finnish Native, thanks for bringing up the issue of final shape after tillering.  This is a fundamental question: How much should set and tillering affect the final shape of a double-curve bow?

My answer.....NOT AT ALL. Nada. Zip. The goal is to induce the least amount of set during construction and shooting.  This is true for ANY bow.  It is a fundamental principal.  Of course, set is nearly impossible to eliminate but the goal is to minimize it.....not use it as a shaping tool.

So, yeah, I respectfully disagree with the idea that no deflexing of the outer limbs is necessary.

[YewArcher]

Yes, agree. The shape of the bow is set prior to tillering the bow. The way you are proposing Finnish would either break the bow real realy in the tillering process orwould end up being a real dud. I think that Tim Baker tries that in one of the TBB.He describes how they bent a bow like that in the middle and trid to tiller it to take the gull wing shape with a broken bow resulting every time. I think it was Tim. Besides its much easier to just create the whole shape prior to tillering. More predictable as well.


Steve

[M-P]

Hi Folks,   From what I can find in the literature, Patrick is right in saying that the originals were shaped into the gull wing shape before tillering.  A bow that is reflexed at the handle and straight limbed will also take a gull winged shape when strung.  I think the second option increases perfomance by increasing early draw weight.  See my example made from rocky mountain juniper

Ron

[a finnish native]

what M-P said. you tiller the bow so that the wood bends from everywhere, and the handle being a tad stiffer will remain reflexed. I have to say that I have made several gull wing shaped bows. not for one have I defleced the limbs before tillering. it takes the shape automatically. And those bows of mine still contain reflex after several hundread shots.

[El Destructo]

thats what I do to mine also....the Shape is pre-tiller

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[JackCrafty]

Awesome!  Thanks for the pics guys.

It seems there are various interpretations of double curve (gull wing) bows.  As for me, I try to focus on reproduction bows.  After careful study of Native American designs, there seems to be one characteristic that stands out:  Plains Indian bows are simply "curved" D-bows.  They perform basically the same, and are tillered the same, as D-bows.  The primary difference is the decreased brace height of the double curve bow design.

Any characteristic that improves the performance of a D-bow will also improve a double curve bow.  Less deflex in the upper limbs is a good performance enhancer (as M-P mentioned) and so is recurved tips, narrowed tips, wider limbs near the handle, etc.....and there are Native American bows with these characteristics.

The reason(s) behind why Native Americans often liked to deflex the tips of their bows is a mystery from a performance standpoint.....but many NA bows have them, so I think they are an essential element.

IMO, a bow with a reflexed stiff handle and slightly reflexed, slightly deflexed, or straight limbs is simply a reflexed stiff handle bow.  The design is efficient for long lengths but not for a compact bow....unless the limbs are quite wide.  I would say that a reflexed stiff handle bow is more like a Sudbury bow than a plains double curve bow.

[JackCrafty]

There is also the issue of the ability of the handle area to remain reflexed during the life of the bow.  Many bowyers make the handle stiffer so that the reflex will not "pull out".  Some woods are better at keeping this reflex than others.  IMO, if you are using wood that does not hold a reflex well, it is not suitable for a double curve bow.

The way to get around this, of course, is to find a stave with the natural shape of a double curve...which is not too difficult if you've got thousands of acres of woodlands to rummage through.  I don't know about you but I certainly don't. So...I've experimented with quite a few species and here is my list (best first) of suitable wood for double curves:

Osage
Juniper
Elm
Locust
Mulberry
Other low to medium stiffness, high tensile strength wood
White Oak
Hickory
White Ash