Why Crown Sinew?

[DuBois]

Just something I been thinking over for a while.
It seems common knowledge to run a crowning course of sinew and I get the idea of putting the sinew to work more because it shifts the neutral plain away from the belly, but if your belly is primarily flat, why not make sinew flat across the back and put more sinew to work than just the crown?
It seems that crowning just uses a lot of sinew (that isn't doing a lot else) to raise the smaller amount of crowned sinew higher.

So...why not a rectangular cross section with sinew?

[hoosierf]

I have run an extra course down the middle to get the benefit of a thicker layer but use less sinew by not putting the layer that thick across the whole width.

[gfugal]

Because sinew is so elastic it can take as high of a crown you can give it. since a higher crown stresses the sinew so much more I think it adds more draw weight than if it was lower but more evenly spread. I think the idea is also what hoosierf said. If you don't place the sinew much anywhere else but in the middle and in working sections, it should supposedly be less weight, not more. You should measure how much sinew in weight it takes to crown it, vs applying it evenly and flat on the back.

[wizardgoat]

Yep, same principle as trapping the back on tension strong woods

[DuBois]

So less mass with more performance by going thin at sides to thick in center.
Figured such but just wanted to hear opinions on if anyone had tried rectangular cross section just for the heck of it.
What if it were a narrow bow? Would that allow an overall longer draw than a crowned wider bow?

[Springbuck]

I'm not really a sinew guy, but I don't think there is much WRONG with a smooth single layer on a square cross section, it just isn't necessary.  Same benefit with a crown of sinew, less sinew (and sinew is heavier than wood), and you don't NEED the sinew at the sides to protect the wood on the sides because the neutral plane has been moved enough to protect both the back and belly side of the wood from strain.

I don't know about that allowing a longer draw on a narrower bow or not.  Not sure I understand the question.  The enemy to defeat on a narrow bow is belly strain, usually, which can be countered by added length, and well made longer bows with an intact growth ring, etc. then don't need the sinew.  A sinew backing WOULD allow a longer draw on a shorter bow by preventing breakage. But, a narrow bow means a thicker bow, generally, and while sinew would protect the belly, too, I think less so as the bow becomes thicker.  The sinew can only stretch so far, and the thicker, narrow bow moves the neutral plane again.

Think about horn bows, which can be pretty narrow, because horn is more compression elastic than wood, and the sinew and horn work together.   Then think of an arctic bow with a cable backing.  Most of those are fairly thin and have a raised or bridged cable, making them essentially thicker front to back.  Does filling the middle in between cable and wood with more wood and making them longer gain you much?  I don't know.

[bradsmith2010]

thats an interesting question, I usually do it cause I am lazy,, I have one even layer, then want some extra poundage so I put a layer down the middle,,   

[PatM]

I think it's a compromise.   Sinew can be strained more by a thicker limb but a wider flatter limb handles belly strain better.  So by crowning the sinew you can essentially make the bow wide and thin and yet still essentially thick at the same time.