Post For Tim Baker ( Sinew)

[Aaron H]

This article, or the one linked to this article, brings up a question for me.  I've heard that you need to prepare your surfaces to be glued no more than 3 days before the glueing process to avoid oxidation of the surfaces. Makes sense. But what I want to know is how deep does this oxidation penetrate into the wood surface?  How far down does one need to scrape or sand the surface to fully remove the oxidized fibres? Is it just the immediate surface, say a few thousandths of an inch, or does this oxidation travel deeper?  Maybe it depends on the amount of time it has been sitting?

[Badger]

   Aaron, I haven't really had much of a problem with oxidation beyond just a light sanding being needed but I have had a problem with the limb cupping and needing to be flattened back out. Mainly on my bamboo I have experienced this but to a lesser degree on osage and other woods. I wonder if light cupping might be misdiagnosed as oxidation?

[BowEd]

I'm not considering myself as an expert here while not a novice either but oxidation is just on the surface IMHO.100 grit is more than rough enough to eliminate oxidized surface.Look at wood darkening over time brought to normal color with a little sanding.Testing shows over time a drop of water on oxidized surface[wood] beads up.After sanding it soaks in easily.JMO yet though but have seen these scenarios many times.
I think you might be over thinking your project Aaron but do think your right in your thinking too as just like getting a good paint job so it is with sinewing and using hide glue for glueing other surfaces too.It all starts in preperation of the surface first.The base!!

[Aaron H]

I haven't had a problem with this either, but I always like hearing other people's thoughts and opinions to help get a better understanding.

[BowEd]

Oh Ok...Sorry about the long winded solilquy response.I hav'nt had any problems of that either.

[willie]

Tim,

interesting info at frets about hide glue

It is never a good idea to dilute too strong a glue to obtain lower viscosity or longer working time when it is possible to use a lower grade of glue.............. high gram strength glues require up to twice the water to reach workable consistency, there will be less glue actually in the joint after it is clamped and the water evaporates.

Have you noticed any bowing due to shrinkage on your glue belly experiment?

[Tim Baker]

Aaron:

Any bad effect of oxidation is fairly insignificant, and then only on lignin. The chief danger when sinewing not-recently-surfaced wood is oil, especially from city air, deposited on the surface. Still, even in Bay Area air, I've never had a sinew to wood bonding problem, even on somewhat aged lumber surfaces. Still, if it's a concern, a very light scraping, or sanding as BowEd notes, fully eliminates any problem.

willie:

" Have you noticed any bowing due to shrinkage on your glue belly experiment? '

Sinew shrinks sideways and well as lengthwise. No problem on narrow thick limbs, but on wide thin limbs sinew shrinking sideways can concave the back, sometimes even cracking the belly. I've never had that happen but it's been reported.

[willie]

" Have you noticed any bowing due to shrinkage on your glue belly experiment? '

Sinew shrinks sideways and well as lengthwise. No problem on narrow thick limbs, but on wide thin limbs sinew shrinking sideways can concave the back, sometimes even cracking the belly. I've never had that happen but it's been reported.

Tim, let me ask a different way, seeing how you have experiments going with both sinew backs and glue bellies, can you comment about any shrinkage going on with the glue belly ones? Shrinkage that might put the bow into deflex as the glue dries?

[Tim Baker]

willie:

The pictured thin amount of dried glue belly pulled the wood into about the same amount of deflex that a same-thickness of sinew and glue wood. It's a touch less than 1/32" so just an inch of deflex. I'm expecting a 1/8" thickness to yield considerable deflex, on it's own, without being forced into position when applying the glue. 

[Badger]

  I had no idea that hide glue had any real properties worthy of consideration. Interesting.

[sleek]

And if you sinewed it first, it would be prestressing the sinew.

[willie]

dried glue  (on the) belly pulled the wood into about the same amount of deflex that a same-thickness of sinew and glue wood.

hmm, so now I have to wonder if it is the glue or the sinew that does most of the shrinking when applied to a back. I would like to think it is the sinew, or other wise if glue shrinks more than sinew, then sinew in matrix might be getting compressed rather than pretensioned when drying occurs.
 The admonition to not dilute the glue too much may because excess water causes more shrinkage. Could the lighter glues that need less water to have a workable consistency actually be better for this application?

[Tim Baker]

Badger:

"  I had no idea that hide glue had any real properties worthy of consideration. Interesting."

Me too till recently. Google doesn't point to any non glue-like uses over time. Hard to believe. When you hold chunks or strips, or mixtures with wood or other natural fiber in hand, uses leap to mind. 

The 54" redwood bow holding the pictured dried glue belly weighed 5.5oz bare. Should have been more precise because the glue belly raised its weight by less than half an ounce. Eager to see what it will do once sinewed.


willie:

A 7" sample of hide glue just dried to 6", another 51/4" sample dried to 4 3/8"  That's a lot of shrinkage. And at up to 10,000-plus psi tensile strength it's going to do serious pulling, as in pulling chips free from glass as it dries. Jeff Schmidt, of the Korean Archery chapter in TBB-3, was  startled one evening by an explosion in the next room; he'd left wet hide glue in a glass container that morning. Lots of hide glue glass chipping how-to on ebay.

[Tim Baker]

I mean YouTube:  https://www.youtube.com/watch?v=sOVDtOok-c8

[BowEd]

Interesting....Do you think lower density type woods will reflex more than higher density?Just a thought.I'm sure more experiments are needed for that.Maybe more elastic type wood is more suseptible to it also.