Putting a sinew backing on a wooden bow will improve the bow in a number of ways. It will keep fibers from lifting up on the back of the bow, and thus help prevent the bow from breaking. It will help keep the bow from following the string (the tendency of the bow to stay a little bent after you have un-strung it). It will give the bow more snap when you release an arrow, and it will increase the draw weight of the bow a little. For all of these reasons, sinew backing is a good policy with wooden bows; and I rarely build a bow anymore that I don't sinew back.
I am currently building a bow for a friend's little boy, so I thought this would be a good opportunity to do a post on how to sinew back a bow. The bow in question is thirty-six inches long and made of hickory. Hickory is a very good bow wood, but it is a little sluggish on release and it does have a tendency to follow the string. A layer of deer sinew on the back of the bow should eliminate the string follow and give the bow more snap. Pictured below: The bow that I will be sinewing
To sinew back a bow you will need the following:
A wooden self bow (see posts of January 25 through February 15, 2009 on how to make a wooden bow)
Some liquid detergent
A hacksaw blade or coarse wood rasp
Something to hold the bow while you sinew it
Sinew fibers (see post of November 7, 2011 on how to prepare sinew)
Rawhide glue (see post of November 27, 2011 on how to make rawhide glue)
A brush to apply the glue with (see post of February 20, 2012 if you want to make your own brush)
A cook pot and heat source
A lot of clean water
The question is often asked, "How much sinew does it take to back a bow?" I've tried to work out some kind of formula for this, but I haven't had any luck. There are just too many variables. Sinews come in different thicknesses and different lengths, bows can be wide or narrow, they can be long or short. You may just want one layer of sinew on your bow, or you may want four or five. I guess you could figure out how many grams of sinew it takes per square inch, but my guess is that you would probably be wrong. With the type of bows I usually make I figure four to six sinews per layer of backing. I always do up more sinew than I think I'll need. That way I don't run out in the middle of backing a bow, and I can always use the excess on the next bow that I make.
I like to use a trick that I learned from one of Jim Hamm's books to help keep my sinew organized while I'm backing a bow. After you have your sinew separated into fibers, sort it into little bundles of six to eight strands. Take these little bundles and put them in an old magazine with a page separating each bundle. All you have to do is turn the page and you will have a new bundle of sinew fibers ready to use. Pictured below: Sinew organized in bundles between the pages of a magazine
The first step in preparing a bow for sinew backing is to thoroughly wash the back of the bow with detergent to remove any oils that might be on the bow. If the back of the bow is not clean when you sinew it, the sinew may separate from the wood when you draw the bow. So, don't skip this step. Some people wash the back of the bow with a lye-water solution. Lye has become increasingly hard to find. Somebody told me that it is used somehow in the process of making meth, so a lot of stores have quit carrying it. I don’t know if that’s true or not, but I do know that our local grocery store doesn’t cary it anymore. So now I just wash my bows with detergent and it seems to work fine. Pictured below: top, Washing the bow back: bottom, drying the bow
Step two is to rough up the back of the bow so that the sinew will adhere to it better. You can do this by dragging an old hacksaw blade along the back, or you may use the coarse portion of a wood rasp. You're not trying to remove any wood. Just scratch the surface up a bit. Pictured below: roughing the bow back with a hacksaw blade
When you have the bow roughed up it is time to warm up your rawhide glue. I am using unflavored gelatin for my glue. Most people don't realize that gelatin is made from powdered beef hide. Don't tell your kids this or they will never eat Jello again. All you have to do to make your glue is dissolve the gelatin in some warm water. I put a pot on the stove and heat about two cups of water and then stir in about three of the small packs of gelatin. Don't cook the glue; just warm it up. If you can't dip your fingers into it, it is too hot; and it will cook the sinew and make it useless. Pictured below: Mixing up some rawhide glue
When the glue is ready, take your brush and paint a coat of rawhide glue onto the back of the bow to prime it. Give the glue about ten minutes to set up and it will be time to start applying sinew. Pictured below: sizing the back of the bow with rawhide glue
In the next post we will apply the sinew.