With all respect, Gentlemen,
I have tested several glues that I have considered using in my shop. We
do harps, and usually don't do lutes, so the stress we contend with is
much greater than any lute ever had to sustain. The test was simple - a
piece of maple one in. square by about a foot long, the test pieces,
also of maple, being one inch wide by a foot long, glued perpendicular
to the first maple piece. The glue area was therefore one square inch.
Each piece was glued using a different glue.
We tested Titebond, Titebond II, Luthier's Mercantile PVA, Gorilla
Glue, another Polyurethane glue, several epoxies, and fresh hide glue
made to a 1 part dry granulated glue to 1.5 parts water. Once the test
pieces were glued and clamped to the base piece and allowed to dry for
48 hours they were loaded with weights. Each test piece had the same
weight attached to the end so that the joint was loaded in peel mode.
The two glues that survived the longest were West System epoxy and fresh
hide glue. The polyurethane glues failed immediately. They really suck!
Titebond and the other PVA glues began to creep and failed in a day or
so. Luthier's Mercantile glue lasted the longest. The hide glue and
epoxy survived a week., when the whole contraption was broken down and
used to kindle the shop stove.
Perhaps this isn't definitive, but it was good enough to keep me from
using any PVA (aliphatic resin) glue in an application that is stressed.
Another point of reference. I have restored several harps (about 30)
that are well over a century old. I have done some that date from the
very early 1800's, and one from the 1780's. As long as the instrument
was not exposed to high humidity or allowed to get wet the glue joints
have been good. Needless to say these were hide glue joints. I'm
presently working on two harps made in Paris about 1780. There are a
few joints in one that need re-gluing, and most of the other is in bad
shape, but the laminated columns on both harps are sound and usable.
I actually have to re-glue more on harps built since 1957, when the
makers began using PVA to assemble their harps, than I do on a 19th C
instrument.
Another issue is the repair factor. Have you ever tried to disassemble
a joint made with PVA?
I use epoxy when I am certain that some poor bastard isn't going to
have to disassemble my work after I'm gone, and when the stress on the
joint is high. I use Super Glue (CA) often, especially on lightly
loaded joints and ornaments. PVA, from Lee Nielson, is used where there
is no sustained stress and I'm certain it won't be disassembled, and
that only because it is easy and very convenient. I use fresh hide glue
for non-creeping joints that may need disassembly so a component can be
replaced without collateral damage.
Howard Bryan
www.hbryan.com
Rob Dorsey wrote:
Honestly, I'm really not trying to start trouble but...you're saying that
you know what the strength of your shop mixed, recycled (and don't try to
tell us you don't re-heat the pot) dry hide crystals of also unknown age
is?? By what measure and to what standard? Got data? Do share.
Seriously a premium modern glue is at least equal to and arguably stronger
than 400 year old ox hoof and fish head glue. And that includes Titebond
liquid hide glue. A quick sniff of most glues satisfies the freshness and I
would love to see empirical evidence of failures including "creep" which I
reckon is a throwback to guitar making, particularly the steel stringed
ones. Friends don't let friends use any glue on an instrument which cures to
a plastic state and at lute tensions, creep is a theoretical phenomenon.
The only hide glue I use is for the top. And this because it may needs be
removed when - notice, not if - someone drops the thing on the hardwood
floor.
Best,
Rob Dorsey
http://LuteCraft.com
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