Tension Cracks in Sinew Backing

[Marin]

Okay, I'll bend it down 2 more inches and inspect the curve, and take some pics for you to see.

[Marin]

Pulled it two more inches. Still getting some cracks when I pull it on the long string to string it, but not cracking noises occur with the low brace tests still.
Checked bend and it still appears to be bending evenly. Even bent it back and forth a bit to see the movement of the outer limbs, and they appear to be bending evenly compared to the rest.
Any thoughts?

[superdav95]

With a bend like that I would proceed.  Unbraced looks good too.  What powndage are you at low brace?

[Marin]

Haven't measured it exactly yet but it feels close to 20 lbs, maybe slightly above. Am targeting 40 lbs at full draw, which for a short bow like this will be around 20". Even if  I can't make that, most of these bows were probably close to 35 lbs in draw weight.
Good to hear about the tiller. So you think the cracks occurring only in this one spot are not indicative of overstressing of this limb portion?
Also, was curious about your take of how I should proceed. I was thinking about tillering further with the short brace like this till I get the tips bending around 10 inches or so, before trying to brace it fully. Should I stick with short brace for longer?

[superdav95]

Marin.  I haven’t made a shorty this small yet myself but based on my experience with slightly longer bows say around 55-60” ttt I would get the brace looking as close to perfect before proceeding on a bow like this.  I would not worry about those tips bending yet till further in the draw.  It’s hard to tell if they are working much now at your low brace but I suspect once you get out to the last few inches of your draw you’ll see them bending a little.  I would get the bend looking balanced on both limbs at your desired brace height.  I have found with my more reflexed bow with sinew I have better luck taking my time on getting to perfect or near perfect looking brace then proceeding from there.  Doing it this way may be a lot more work initially but saves time later on in the tiller.  I’ve had it on some where very little tiller scrapes were needed for tiller and balancing the limbs out to almost full draw if the time is taken to get to brace with perfect looking bend.  As for the cracks… it’s likley not an issue but it’s hard to know from pictures really.  Typically sinew dose t fail across its fibers this way.  The failures I e had with sinew bows is usually not sinew related.  I’ve had some sinew lift off of limbs and delaminate on me but never fail itself.  It very strong.  The wood will fail before the sinew.   I ussaully stick to 1/3rd sinew thickness or under to 2/3rds wood core.   On these bow I would use a long yard stick method for tillering to brace for perfect brace tiller.  I can’t remember where I saw this method but it’s great.  I did a quick google search and can’t find it now but basically it’s taking the length of your limbs and measuring to find your mid limb point and make a mark.  In your case use from the middle of where the handle would be to just before the recurve tip bend at the belly.  As you bend it get it to the point initially where both limbs are straight at the same time using long string.  I know you are passed this point now but for future reference.  In your situation now you would just get it to your low brace again on your tiller stick and use the measurements marks at mid limbs using your yard stick or ruler and hold it up to the belly and having a look to see if the bend looks balanced on both side of the mid limb mark on each limb independently.  This hyper focused approach has saved me on some of my more complicated projects.  I also measure the depth from the belly mid point mark to the ruler or yard stick.  This measurement I compare with the other limb doing the same thing.  I hope this make sense.  It’s not a tiller method I use all the time but for these highly reflexed bows I do.  My bamboo bows I sometimes do as well as they are static levers/ siyahs.     Try it you might like it and it’s pretty simple method.  It may seem overly tedious initially but it’s a good method that takes some of the guess work out of such short bows where it can be tougher to see potential problems in the bend.   By hyper focused attention on each limb using measurements too small for your eye to always catch could be a good alternative for ya.  Hope this helps.  Any more questions just message me

[JW_Halverson]

Those cracks are just excess glue.  I would be very surprised if your sinew failed here.  My experience is that the wood will fail first.  The sinew may lift off or pull away or delaminate from the wood due to a sizing issue or something but the sinew is crazy strong.  If the sinew was of good quality and not pounded to death or over heated it will be fine.  I would consider also making yourself a stringer if you don’t already have one.  Here’s a few pics of one I made last year.  I got the idea to make my own like this from bowEd on here.  At the time I was neck deep into a highly reflexed bow and needed a specific stringer for this bow.  Here’s a couple pics.  Hope this helps ya.  Good luck.

Hey superdave, would you make a post about how you make those bowstringer cups? I like them better than the stuff I am doing.

[superdav95]

Those cracks are just excess glue.  I would be very surprised if your sinew failed here.  My experience is that the wood will fail first.  The sinew may lift off or pull away or delaminate from the wood due to a sizing issue or something but the sinew is crazy strong.  If the sinew was of good quality and not pounded to death or over heated it will be fine.  I would consider also making yourself a stringer if you don’t already have one.  Here’s a few pics of one I made last year.  I got the idea to make my own like this from bowEd on here.  At the time I was neck deep into a highly reflexed bow and needed a specific stringer for this bow.  Here’s a couple pics.  Hope this helps ya.  Good luck.

Sure I can do that. 
Hey superdave, would you make a post about how you make those bowstringer cups? I like them better than the stuff I am doing.