Sinew backing?

[MikeWinVA]

I have just rough tillered a Mollgabet style of bow.

It is about 72".  The working limbs are about 2.25" wide and 17" long with 2" fades.

I am using some fairly dense red oak that has about 4 growth rings per inch.

Will sinew backing the working limbs over power the belly of the bow?

[LittleBen]

In college one of my friends had a little handheld 20 questions game, and we eventually had to make a rule that you could only answer with "sometimes" twice per game ..... My point? That the answer to nearly every question can be sometimes.

Red oak is tension strong. A clean back on a red oak bow will not fail before the belly frets (assuming you don't just yank it back suddenly without any tillering or anything). So in a sense you should expect red oak to overpower red oak.

So will sinew overpower the red oak? Who knows. The answer is probably sometimes.

Let's take a step back though ... What do we mean by overpower? If we mean that the belly will fail before the back, then yes probably the belly will fail first.
Will the belly fail on your bow? No idea. What draw weight and length are we talking about?

Personally I wouldn't sinew that bow. If you need a backing, which you may not depending on grain, consider something simpler.

Just my .02 ....

[MikeWinVA]

Draw weight 55ish and 27" draw length.

None of the red oak that I have backed have failed from grain orientation. I have used heavy duck canvas with TB2 to back the them, and noticed that there was little or no change in draw weight. Most of the failures I have had are from poor tillering.

[mikkekeswick]

No - it cannot.
Sinew has low stretch resistance and can stretch about 8 times further than your wood can compress.
'Overpowering' is a when you have a big difference in between back and bellies relative strengths/resistances to bending.
Most woods are stronger in tension than they are in compression (not all) and this is why we see chrysals - the woods relative strength in tension was enough that it didn't fail there it failed in compression. A chrysal is the woods belly cells literally collapsing after there resistance to compression is reached. If a wood was weaker in tension than it was in compression then you would see a lifted splinter on the bows back before you saw any chrysals.
Sinew has very low stretch resistance compared to wood and will basically allow you to keep drawing a bow until you find its compression limit. It takes load off the belly so in essence it does the exact opposite to overpowering.
If you took a piece of bamboo and backed a piece of pine with it then yes this combo would almost certainly overpower the belly. Bamboo has grerat resistance to stretch and pine has little strength in compression = chyrsals everywhere! If you had to make a bow from a tension strong, compression weak wood eg.cherry then you would trap the belly to give the back a chance. People often dismiss these sort of woods as 'brittle' etc but it you understand the properties and do your best to even up the relative strengths (via trapping) of what you are using you find that great bows can be made from all sorts of woods/combos that 'don't work'.
A simple bend test is your friend when figuring all this stuff out.

[John Scifres]

Since I have never done it, I can offer little direct evidence.  I think it should be tried. But I think that about everything.  I doubt that it will overpower the belly.

What is your goal for the sinew?

Some thoughts:

I would never sinew back a bow that I had not specifically intended it for.  It's just too much work.

Sinew shines on short bows where its relatively high mass (to wood) will not cause efficiency problems.  

Sinew is great when it is working really hard.

72" bows drawing 27" are generally not working really hard, even in lever design like that.

I would not sinew back a 72" bow.  Seems to be mixing up design concepts.

Personally, I would not sinew back red oak. But I am osage rich.

Good luck.  Share your results.