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Questions about sinew backing
Aaron1726:
--- Quote from: willie on May 08, 2023, 09:40:20 pm ---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
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Thanks Willie, I'm gonna keep that in mind and try not to have this one end up like the last one :)
Aaron1726:
--- Quote from: bassman211 on May 08, 2023, 11:08:32 pm ---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.
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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:
--- Quote from: Aaron1726 on May 10, 2023, 06:40:39 am ---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!
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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
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