Sinew Backed, Double Curve Bow

[Papa Matt]

Yes, Pat...More info on the fish glue please. Also, you said Ishi used to decrown his bows and violate rings to get a flat, level, surface for the sinew...is this to say that you should not sinew a round-backed bow, only de-crowned bows? Do you have an opinion on this?

~~Papa Matt

[JackCrafty]

The fish glue I use is made for furniture restoration work (among other things).  It is liquid at room temperature and does not need to be mixed or heated.  The manufacturer says the formula is fish glue, a small amount of glycerin, and a deodorizer.

There are various commercial sources for fish glue (just google it).  Some of it can be pricey.  Isinglass is the most expensive (fish bladder glue).

I suppose I could make my own....someday.

As far as flat surfaces for sinew, no, the surface can be rounded as well.  I was referring to the way the growth rings are violated on wide limb paddle bows made from juniper.  A straight grained stave of juniper is a VERY rare thing.

[JackCrafty]

Here are a couple of photos of a Native American double curve bow showing a single layer of sinew on the back.  (A friend sent me these photos of his bow when he asked me to make a new string for it....the string in the photos is too thin and was made for display purposes). Anyway, the length of the bow is 40"....and the draw is probably 20" (typical of most NA bows of this type).  It appears that the sinew is a safety feature (to help prevent breakage) rather than a performance enhancer.


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[JackCrafty]

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[Papa Matt]

That's a bow that your friend made? It looks old. I would have guessed it came out of a museum. What wood was used for it?

~~Papa Matt

[JackCrafty]

The bow was made by an Indian, from the late 1800's...and my friend is an antiques dealer.  He thinks it's Apache in origin.  Not sure about the wood.  I would guess that it's mulberry (a favorite among Apache bowyers).

[Papa Matt]

Ohhhhhh I see. That's pretty neat. Was the double curve the most popular horse bow at the time?

[JackCrafty]

Matt, it's funny but I've heard that the Apache's didn't like the double curves that much...they preferred a simple D-bow.  As far as the horse culture goes, yes, I think the double curve was as popular as the buffalo hide tipi, long-flectched arrows, and the war shirt (during that time period).

[JackCrafty]

1. Jute twine wrapping removed from bow (today)....6 days after wrapping.  You can see the fuzz of the twine left behind.
2. This is easily removed with a light sanding with 120 grit sanding sponge - using a circular motion.  I try not to sand through any of the sinew.
3. Jute fibers removed.
4. Applying a coat of fish glue over the sinew (straight from the bottle).  This is let dry for a few hours.


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[JackCrafty]

1. Adding temporary "shoulder" nocks to tips of bow.
2. Loop and 4 strands of poly twine (temporary bowstring).
3. Loop placed over upper tip.
4-6.  Tying off lower end. There is a little slack in the string.  The bow is not braced.

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[JackCrafty]

1. Marking center of bowstring.
2. Drawing for the first time (slowly).
3. Checking tiller @ 18" draw with the slack string.  Looks like the right limb has a flat spot.
4. 42.7 lbs on the scale.
5. Removeable pegs on the tillering stick.

Note:

I've read several posts that suggest that sinew should dry for at least 2 weeks before tillering.  The reason I don't wait that long is because of three reasons:  (1)The climate is dry here in West TX  and (2) I make an effort to keep all excess water and glue out of the backing (I don't soak the sinew in water, I dunk it, and I wrap the sinew with firm pressure so that all excess glue is squeezed out).  Also, (3) I put on one or more thin layers of sinew....not a thick layer all at once.

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[JackCrafty]

Checking set...

1. About 15/16" distance in the center immediately after tiller check (the bow was left in the tiller stick for 10 minutes).  The original distance was 1-1/8" (before sinew).
2. About 1-1/4" on the left (upper) limb.  The original distance was about 1".
3. About 1-1/8" on the right (lower) limb. The original distance was about 1".

Overall, very little set....but i still need to finish the tillering @18" draw, "sweat" the bow for a little while, relax it for a day, then shoot it a couple times to check for hand shock.  I don't expect more than 3/4" of set on the limbs at this point.  I will then add another layer of sinew over the entire back and sides for additional safety because of the relatively poor quality of the stave.

I will not be using the jute twine wrap over the second course of sinew. This should give the sinew a smoother look. I normally let the first course of sinew dry a bit longer but the weather's been very dry lately.  However, I'm not going to draw it to 22" until the second course of sinew is dry.  I will then wrap the tips (with sinew), add sinew shoulder nocks,  and add sinew wraps in the center and at intervals along the limbs.


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[JackCrafty]

1. Bow braced at 4".  Draw weight is 5.5#@1"
2. Bow drawn to 10" ...24.0#
3.  Bow drawn to 12".....29.8#


At this rate, I'm on track for a final draw weight of close to 60# (assuming I don't remove any wood).  For 60# final weight short bows, here's the numbers I use:

60#@24"Draw
55#@22"
50#@20"
45#@18"
40#@16"
35#@14"
30#@12"
25#@10"

If the bow is pulling 25#@10", then it's on track to pull 60#@24".

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[JackCrafty]

I decided that the upper limbs needed to bend more and that the middle was bending too much....so I thinned down the upper limbs and re-tillered.  The new draw weights are:

22.7#@10"
27.9#@12"

I'm now on track for 55#@24" draw but that's OK.  I'll try for 60# with the next bow.   Here's my chart for 55# bows:

55#@24"
50#@22"
45#@20"
40#@18"
35#@16"
30#@14"
25#@12"
20#@10"

The last pic shows the bow drawn to 18".  The limbs aren't bending in perfect arcs yet but I'll stop messing with it for now.  I'm going to add a second course of sinew before I do any further tillering.

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[JackCrafty]

Measuring set:

1. Bow braced at about 4" for about 30 min, then string removed and let rest for about 15 min before measuring set.
2. Center distance about 15/16".
3. Measuring set in right limb.
4. Right tip distance (upper limb) about 1-1/2".
5. Left tip distance (lower limb) about 1-1/4".

The tiller is asymmetric at this point....but from what I've learned recently, this might not be such a bad thing.

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