Questions about sinew backing

[Aaron1726]

Hi all, I am working on a replacement short bow for my failed sisal backed one.  I got my hands on a good hickory board and have a 42 in bow tillered out to about 40lbs at 17in.  Now I'm looking to add a backing, I thought about sisal again, but I kinda want to give sinew a try.

So my questions...  first, does anyone have any idea how much sinew I would need to back this one?  It's 42" long, 1.5" wide in the middle 8in and then tapers to 1/2" tips.  Would like a little performance, but not looking to go overboard on how the sinew so I'd guess maybe 2 layers at the most?  Finally, I thawed out several backstraps to make jerky and trimmed the sinew off the back to add to the few I already had dried, is there any issue with using sinew that's been frozen and thawed like that?  If it's good to use, I may have more sinew in the freezer that I had realized 

Thanks in advance for any help or guidance, really appreciate it.

[willie]

what is your intended draw length?

[Aaron1726]

Willie, was really only looking for about 18in or so, not sure how much more I could get from this one, maybe 19in?

[willie]

seems ok, I was thinking that overdrawing your previous one might have been too much

not on account of the typical stress increases one see with overdrawing, but if i remember correctly. a bendy handle can be subject to disproportionate levels of stress of one goes beyond the 2:1  bow length: draw length ratio

[bassman211]

One good layer of sinew should do it for you. I have made quite a few 38 to 50 inch sinew backed plains bows, and one good layer of sinew has worked well for me. Draw lengths to 20 inches on the short bows, and draw lengths up to 25 inches on the longer ones.

[Aaron1726]

seems ok, I was thinking that overdrawing your previous one might have been too much

not on account of the typical stress increases one see with overdrawing, but if i remember correctly. a bendy handle can be subject to disproportionate levels of stress of one goes beyond the 2:1  bow length: draw length ratio

Thanks Willie, I'm gonna keep that in mind and try not to have this one end up like the last one

[Aaron1726]

One good layer of sinew should do it for you. I have made quite a few 38 to 50 inch sinew backed plains bows, and one good layer of sinew has worked well for me. Draw lengths to 20 inches on the short bows, and draw lengths up to 25 inches on the longer ones.

Thanks.  Any idea how much sinew would be needed for one layer?  Never done it before so trying get it all planned out before I just dive in.  I just weighed what I currently have, 32 grams.  Doesn't seem like enough, but like I said, not sure that "enough" is.

And any thoughts on using pre-frozen sinew?  I assume it's ok, but don't just want to assume anything...

[superdav95]

I agree with what bassman says here.  One good layer will be good enough for ya.   As far as amount of sinew to use I would say for a bow this length and width I would use 40-50grs dried weight should be enough.  You’ll add the same weight in hide glue again. So maybe adding 80-100 grams of mass to your bow overall not including any other coverings and or finish.  If it were me doing this bow build I may consider starting with 15grams per limb total of 30grams dried weight and see where you are at.    You also need to consider this… what length is your sinew?  If I were doing this build I would save all my longest strands for my final layer on each limb.  Your working bending area is fairly long despite it being a short bow.  You’ll need to sinew your bow equally over the entire bending area of the bow which includes the middle handle area.  I would organize all my available sinew and organize it all according to length in bundles.  I would comb it well to get all the extra casing bits and fatty bits out.  You want to measure your dry weight in as clean as possible strands separated into bundles according to length then evaluate the amount you have.  Freezing sinew should be fine. I’ve used much sinew previously frozen from my local butcher without issue.  As far as laying it down on your bow there is many many different ways to do this.  I personally like to rough up my bow back with a fine toothed 20tpi blade and clean with wire brush to prep it.  I then size the back thoroughly prior to laying down the sinew.  This involves applying several coats of very thin hide glue to soak into the bare bow wood back until it becomes shiny in appearance.  You’ll know it’s sized enough when it shines when dry.  This will help immensely with sinew adhesion. Usually about 6-8 coats will do it.  Laying down soaked wet clean bundles weighted and measured of sinew in an organized manner will more likely give you a favourable result with little to no tiller tweaking afterwards.  I would carefully look at what sinew you have when dried, cleaned, combed and separated into bundles of similar lengths.  If you get to your 30-40 grams in your first layer and the bow dries for a couple weeks you can start bending it safely.  Some circumstances may allow it to dry faster but better safe.  If bow bends well and it is in the poundage you lime and it shoots well I would finish it up.    If it is still feeling like more is wanted you can add another 20 grams.  My hesitation in adding more then 40 initially on first layer and maybe only layer is that you may rob performance with adding too much mass.  This bow will have a fairly short draw by the limits of its size you want to keep the mass down to as low as possible.  This will likley land you with similar performance as your sisal backed bow maybe little more performance.  The major advantages of the sinew will be improved strength and recovery of the bow.  You’ll also notice that it has a different feel to it compared to a material like sisal linen materials.  It feels more alive and married to the wood and becomes a new thing.    It’s hard to explain but noticeable.  There’s lots of info here and many guys here willing to help and share experience.  I’ve been the benefactor of this generosity of guys here.  If you are looking for good quality clean sinew I would reach out to Eric Garza on here.  I used him last year for some in a pinch and it was great stuff.  Just a thought if you end up little short on sinew.  Hope this helps ya.  Reach out anytime. 


Dave

[Aaron1726]

Thanks Dave!  That is really helpful.  I think I'm going to get what I have now cleaned up and combed out like you suggest and weight it again.  I will then see just how much a have and of what final lengths.  Sounds like I may still be a little bit short, but I still have a few backstraps in the freezer still, so might be good.  I like the idea of sourcing from the butcher too.  We have one here in town that I might go talk to and see what they might could provide.  I have the word out to family and friends for this fall to send their sinew my way so gonna start trying to amass a bit for future projects, hopefully.  I generally take only 1 deer every year, and haven't saved any until recently.

As for sizing the back, is it OK to go ahead and size it, even if it may be a month or 2 before I finish backing it?  If I get a chance to work on it I had thought of going ahead with this part in advance.

Thanks again for all the help!

[superdav95]

Thanks Dave!  That is really helpful.  I think I'm going to get what I have now cleaned up and combed out like you suggest and weight it again.  I will then see just how much a have and of what final lengths.  Sounds like I may still be a little bit short, but I still have a few backstraps in the freezer still, so might be good.  I like the idea of sourcing from the butcher too.  We have one here in town that I might go talk to and see what they might could provide.  I have the word out to family and friends for this fall to send their sinew my way so gonna start trying to amass a bit for future projects, hopefully.  I generally take only 1 deer every year, and haven't saved any until recently.

As for sizing the back, is it OK to go ahead and size it, even if it may be a month or 2 before I finish backing it?  If I get a chance to work on it I had thought of going ahead with this part in advance.

Thanks again for all the help!

Aaron.  No problem at all anytime.  As for the sizing it don’t really matter too much I you size it now a week or so before you lay sinew.  What does matter more is when you rough up your back to prep the surface for sizing you’ll want to do that the same day as you size if you can.  Also something I do that was shown to me is to use radiant heat source like a stove element or something that isn’t forced air heat to heat up your surface just before the first few size coats to really let it get down in there to the wood cells and fibers as deep as it can.  As it cools it will draw the watery glue down in deeper.  Deeper is good for glue and holding the sinew.  Best of luck with it and sounds like a fun project.   

Dave

[willie]

Nice instructions and tips, Dave !

@all
what is the easiest way to strip dried tendons into fibers? do you soak them much first?

[superdav95]

Nice instructions and tips, Dave !

@all
what is the easiest way to strip dried tendons into fibers? do you soak them much first?

Willie.  I use a wood on wood and pound it.  I use a section of muscle wood sapling to hammer with on a stump.  I twist the tendon as I pound it to get it broken up good.  I get less breaks in the fibers this way.  Leg tendons are little more work but yield more sinew fibers.  Back sinew is the easiest to process but not as much yield.  They do give more longer sections though depending on the animal.  Once I pound it well when dried I use my hand to separate the fibers into as many long strands as k can.  It will have some casing on it after pounding it but this can be resolved with a steel dog brush or wire brush.  Once you get it fairly fine hair like strands I use wire stiff brush again and then weight it all and separated into length bundles.  If doing a bow like Aaron’s the last layers should be the longest ones.  On a stiff handle bow you can measure out your bundles and then divide in half for each limb.  Just prior to laying down I wash with dawn soap really well and use a clean surface to comb it out again as pre measured bundles.  This is done with little wire brushes I use stainless steel brushes. This gets more of the unwanted little bits out and makes for a very clean sinew job in the end.  This method gives a fairly accurate measured way to get the same amount of sinew on each limb.  When I actually lay the sinew down I use the dunk in the glue method.  I keep the sinew in it water and wring it out of excess water with fingers then dunk into the glue and wring it out and down on the bow.  I also brush on a layer of glue on the back of bow just prior to the sinew.   Hope this helps.  Best of luck.  Dave

[Aaron1726]

Really appreciate all the advise yall, thanks! 

I found someone selling leg sinew on etsy. $32 for 1/2 lb, not sure if that's a good deal or not, but seemed cheaper than anything else I had seen so I got it.  Just arrived today and looks pretty good, and several fairly long pieces.  So now I guess it's time to get to pounding it all out and see what I end up with.  I'll start a new thread for the bow and let yall know how it goes.  Thanks again!

[Eric Garza]

I found someone selling leg sinew on etsy. $32 for 1/2 lb...

That is a heck of a deal. Leg sinew is so much work though...

[superdav95]

That’s a good deal.  Keep us posted.