A lack of cohesive strength can for practical purposes be translated to a
lack of gap filling strength. Adhesion generally refers to a glue's ability to
adhere to a surface, while cohesion describes it's ability to form internal
bonds within itself. High adhesive / low cohesive strength would mean
that if forms an excellent bond with a tight joint, ideally in which
individual strands of the collagens are each bonding to both surfaces. If
the joint is not tight enough, they would have to attatch to one surface,
then bond to a series of other collagens to make it across the gap to the
other surface.
As to the gram strength, 167 should still be more than adequate. Most
people use from 192 to 250 though. Above 300 is generally considered
too thick and quick gelling to be convenient for general woodworking.
500 is used to make chipped glass. I don't believe I've ever used the
Behlens hide glue, but Milligan and Higgins doesn't make a 167 gram
strength which means it's imported from outside the US. This doesn't
automatically mean it's bad, but I do know a lot of the imported glues use
more bone and hoof than hide and are considered quite inferior (and
smelly).
Even with lousy hide glue you shouldn't have gotten a clean break
though. I don't know how much you use hide glue, but from what you
describe it really sounds like something went wrong in the glueing
process. As Mike pointed to, there are so many variables - your mixture,
how is your glue heated, could it have gelled before fully clamped, etc. If
the break was totally clean it seems like a mistake must have been made
somewhere.David Collins38776.0882175926
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Seriously,when I glue something,say a head stock, I'll see if I can't knock it off the next day. Last night I took my neck with my HHG headstock and smacked it on the table it snapped off,clean,no wood. But then Mr.Ford says HHG has low cohesive strengh. What does that mean? I emailed Behlan,and they said the glue I'm using is a 167 gram strength,Ford's is 192. HHG ranges from like 30 all the way to 300. Think there's much difference between 167 & 192? Clinton
