Sinew backing advice

[superdav95]

I have this bow that I made earlier this year and I’m looking to add a couple maybe three layers of back sinew to it.  My bow is complete and shoot well but there is a small little knot on the outer 1/3 of the bottom limb.  I’ve put lots of arrows through the bow and it is nice but would like about 55lbs draw weight instead of the 48lbs.  It’s one of my mollegabet bows with a heat treatment on the belly.  The dimensions are…

67ttt,  66ntn,  width of widest part is 1 7/8” which tapers very slightly out to 1 3/4” for about 20 1/2” on the top limb and 19 1/2” on the bottom.  The levers are about 12” each.   The working limb is about 15-16” respectively for the bottom and top limbs taken in to account for the fades out of the handle and the fades at the levers.   

My question is this.  How much sinew (weight) is recommended for adding about 5-10lbs draw weight?  I realize that it’s not likley that simple of an equation as there are so many variables but a ball park would be better then nothing.  I’ve heard guys on here mention 30grams sinew per side on horn style bows bow with the longer limbs maybe more??? Yet my working limbs would be in similar ballpark of about 15-16” as the levers are just that levers and not working per se.  let me know what you think and also would love to here methods that guys are using too.  I have done very little sinew this far and was planning on hide glue to apply the sinew.  Another question…  how much should I rough up the back to prep for sinew.  The back now has 5 coats of tru oil.    Here’s a few pics of the bow

Cheers

Dave

[superdav95]

Some more pics…

The first pic here shows the little know on the back that carries to the belly. 

[bownarra]

Personally I wouldn't sinew an already shot in bow. The problem you have is that to make the most of the sinew you would need to reflex it quite a lot - this is asking the already compressed belly to go into tension - that is a recipe for things to start going south. You can get huge cracks going right across the belly.....true these sort of cracks tend not to be fatal but still....
If you were to do it then I would use 40 - 50 grammes per limb. A hornbow would normally be made with 35 - 50 g per limb.o not rough up the back! Collagen glues work best on smooth surfaces. Sand the back flat with 60 grit intially then go down through the grits and use a very sharp scraper as the last prep. This roughening the back is something that has transferred over from hornbows butthey are not 'roughened up' they have grooves scored into the back. These grooves aren't to help adhesion they are to help stop the core breaking - which isn't an issue with wood bows.

[Tuomo]

These grooves aren't to help adhesion they are to help stop the core breaking - which isn't an issue with wood bows.

Could you please elaborate this, please? How it is possible that grooves are helping to stop the core breaking? I can not get any kind of physical reason in my mind.

This would be great topic in the new Atarn-foorum...

[BowEd]

Not to hijack with pictures your thread here but I've sinewed a few of the same type hickory you have there,but just tillered it to brace and then sinewed it.You might be better off starting another bow for that.I can't say it won't work for you though.I just never did it to a finished bow.I take a hack saw sideways and stroke grooves full length after 100 grit sanding on that varigated muscled up back and size it well before sinewing.Works for me even with extreme reflex induced.
I just finished a few weeks ago [it's curing now] sinewing a winged elm levered bow [62" TTT/,50/50 lever to working limb].Because it was given to me roughed out but cut out to osage width.I knew it would'nt make the poundage from working with this wood before [barely 40#'s].It has a heat treated belly [reflexing 5"] into reflex.Then reflexing further to around 9" after sinewing.I put around 1000 grains on a 3' length of the working limbs and handle estimating to get a little over 50#'s.I'll then tiller it to my draw weight.I figure to get at least an extra 15 pounds or more from that sinew and reflex.Around 25% of the working limbs thickness is sinew now.

[Pat B]

It would be a shame to cover that beautiful back.     If it were mine I'd start another bow with sinew backing in the initial plan. That knot on the lower limb shouldn't be a problem just as it is.

[superdav95]

Awesome thanks for the responses guys!   I think I’ll leave this one the way it is.   There nothing wrong with it I just thought sinew might give me some insurance on that little knot and add a few pounds in draw weight.   

So here is another related question. I have a few of these bows have experimented with heat treatment and such as well as figuring out how to tiller these molles.  One of my earlier attempts in the junk pile is a bow that had pulled a splinter on the back.  Different bow but similar layout.  I’ll post some pics of it too.  I knew I didn’t get the tiller quite right on this one.  It’s about 50 lbs.   I didn’t finish this one up as it failed on me.  I had glued on horn tips to shoot in failure occurred and heard the dreaded tic.  I tried to dribble some ca glue down into the lift but didn’t hold and lifted again.  Can I still salvage this bow with sinew?   I had planned it to be garbage and another bow to be thrown into burn pile but could this be salvaged with sinew backing??? It’s not very deep of a lift as far as I can tell.  This may give this bow another chance perhaps?  I’d likely have to Re tiller it again but I’d be cool with that. Another consideration is rawhide or back with a strip of bamboo even. Let me know your thoughts on this.  In the pics you can see the lift and last pic some vertical checks in the fades.  I wasn’t happy with these checks and think I tried to dry out to quickly.  They ha e been filled in with ca glue and appear to be fine.  Should these also be of concern and maybe not worth the effort to sinew or back at all.  Let me know thanks. 

Cheers

Dave

[superdav95]

Not to hijack with pictures your thread here but I've sinewed a few of the same type hickory you have there,but just tillered it to brace and then sinewed it.You might be better off starting another bow for that.I can't say it won't work for you though.I just never did it to a finished bow.I take a hack saw sideways and stroke grooves full length after 100 grit sanding on that varigated muscled up back and size it well before sinewing.Works for me even with extreme reflex induced.
I just finished a few weeks ago [it's curing now] sinewing a winged elm levered bow [62" TTT/,50/50 lever to working limb].Because it was given to me roughed out but cut out to osage width.I knew it would'nt make the poundage from working with this wood before [barely 40#'s].It has a heat treated belly [reflexing 5"] into reflex.Then reflexing further to around 9" after sinewing.I put around 1000 grains on a 3' length of the working limbs and handle estimating to get a little over 50#'s.I'll then tiller it to my draw weight.I figure to get at least an extra 15 pounds or more from that sinew and reflex.Around 25% of the working limbs thickness is sinew now.

Looks great!  Can’t wait to see it done.

[superdav95]

Personally I wouldn't sinew an already shot in bow. The problem you have is that to make the most of the sinew you would need to reflex it quite a lot - this is asking the already compressed belly to go into tension - that is a recipe for things to start going south. You can get huge cracks going right across the belly.....true these sort of cracks tend not to be fatal but still....
If you were to do it then I would use 40 - 50 grammes per limb. A hornbow would normally be made with 35 - 50 g per limb.o not rough up the back! Collagen glues work best on smooth surfaces. Sand the back flat with 60 grit intially then go down through the grits and use a very sharp scraper as the last prep. This roughening the back is something that has transferred over from hornbows butthey are not 'roughened up' they have grooves scored into the back. These grooves aren't to help adhesion they are to help stop the core breaking - which isn't an issue with wood bows.

Awesome thanks bownarra.  I’m gonna leave this one alone.  I have another bow that lifted a splinter on shooting in that was thinking I could poss salvage.  See the pics of the damage and would welcome your suggestions. 

Thanks again

Dave

[BowEd]

Awesome thanks for the responses guys!   I think I’ll leave this one the way it is.   There nothing wrong with it I just thought sinew might give me some insurance on that little knot and add a few pounds in draw weight.   

So here is another related question. I have a few of these bows have experimented with heat treatment and such as well as figuring out how to tiller these molles.  One of my earlier attempts in the junk pile is a bow that had pulled a splinter on the back.  Different bow but similar layout.  I’ll post some pics of it too.  I knew I didn’t get the tiller quite right on this one.  It’s about 50 lbs.   I didn’t finish this one up as it failed on me.  I had glued on horn tips to shoot in failure occurred and heard the dreaded tic.  I tried to dribble some ca glue down into the lift but didn’t hold and lifted again.  Can I still salvage this bow with sinew?   I had planned it to be garbage and another bow to be thrown into burn pile but could this be salvaged with sinew backing??? It’s not very deep of a lift as far as I can tell.  This may give this bow another chance perhaps?  I’d likely have to Re tiller it again but I’d be cool with that. Another consideration is rawhide or back with a strip of bamboo even. Let me know your thoughts on this.  In the pics you can see the lift and last pic some vertical checks in the fades.  I wasn’t happy with these checks and think I tried to dry out to quickly.  They ha e been filled in with ca glue and appear to be fine.  Should these also be of concern and maybe not worth the effort to sinew or back at all.  Let me know thanks. 

Cheers

Dave

I'm afraid that's going to need a wrap with sinew for sure.You could place one on the other limb to balance the look.Cover it all with rawhide or a thick snake skin.I've used about a 1/32" thick faded out covering with angel hair type flax before with success covering the splinter,then covering with rawhide but since I don't have the bow in hand I can't advice that for sure.Cracks in those fades don't look bothersome to me.

[superdav95]

It would be a shame to cover that beautiful back.     If it were mine I'd start another bow with sinew backing in the initial plan. That knot on the lower limb shouldn't be a problem just as it is.

Thanks pat.  I’m gonna leave it then.