Official Luthiers Forum!

I glued a bridge on a few days ago, LMI glue, and then when drilling holes for the pins through the top, noticed that the glue under the bridge in the center, was less than crystal hard. The bridge had been clamped in place for a couple of days. I wonder how long glue that is not exposed to air, trapped between the saddle and the top, remains unhard.John Kinnaird38718.8470601852

I can't speak for the LMI stuff but I just did another 5 piece neck laminate (4"x4") using Titebond and had it bandsawn into 2 necks after 24 hours. There was no indication that the glue was still soft anywhere along the cut lines.

_________________
JJ
Napa, CA
http://www.DonohueGuitars.com

John, if you were drilling through holes that you had made in your bridge before you glued it to the top (as most of us do), then I would not be too surprised if the 3/16" thick wad of glue in the hole was not cured. Once a big pile of glue gets a skin on it, it takes quite a while to cure.

Smear a thin bit of that glue on a piece of scrap. If it dries normally, then I bet you're okay.

You weren't heating it up with that drill were you?

Colin

_________________
I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

Yes, I was redrilling the holes through the bridge and into the top so skinning certainly happened. And, Colin, perhaps the heat of the drill did soften the glue to some extent. Nevertheless I am left wondering if part of the dramatic improvement of the tone of a new is not in part due to the complete hardening of the adhesives.   Just a thought.

My civil engineer son tells me that concrete takes more than a hundred years to reach full hardness, I am surprised that the crystalisation process in concrete is that fast (the crystal structure of some rocks can still be changing after millions of years). I would think that the crystal structure of glues would not have stabilised for many years particularly if subject to environmental changes.

So, not only do we have to wait 50 years to hear the potential of the wood in our guitars but also for the glue to stabilise. John this is really quite depressing.

Colin

_________________
I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

Colin -

For what it's worth, hide glue does not undergo any chemical change as it
hardens. It hardens by evaporation of the solvent (water) and can be
reactivated to its original state at any time with the same solvent.

Concrete isn't even remotely similar. It can harden under water, for
example.

So, fear not, hide glue gets as solid as it ever will in a very short while.

Oh, yes, and the residual wet glue in the bridge holes is not a problem if the
joint has been clamped and dried overnight.

_________________
Cheers,

Frank Ford

FRETS.COM
HomeShopTech
FRETS.NET

Frank, if you read John's original question you'll see that he refers to LMI glue, neither he nor I mentioned hide glue.

I refer to crystalisation processes, even the evaporation of water in hide glue causes a crystalisation process to take place albeit a reversible one. However, if hide glue is 'dissolved' in water then yes, as it hardens it must indeed undergo a chemical change, only if it is just in suspension will there be only evaporation with no change to the chemical structure.

Colin

_________________
I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

What was your shop temp.? Colder equals a longer cure time. Warmer (definately need over 65 deg. F.) equals a faster cure time. Really, with PVA glue, over 70 F. is best for a 24 hour cure, from what I've read and heard.

I guess I was scanning that post a bit too quickly. I somehow managed to
come up with hide glue, maybe because of the "crystal hard" part. In any
case, I don't think there's much to worry about. A properly constructed glue
joint has precious little glue actually in it, and there's close to a solid
mechanical bond between the two pieces, I think. At any rate, I've reglued
quite a few bridges on instruments where the bond was many decades old
and solid, without hearing a bit of degradation in tone.

In all cases, I allow overnight drying as a minimum for any clamped glue
joint - it's not all that long to wait.

_________________
Cheers,

Frank Ford

FRETS.COM
HomeShopTech
FRETS.NET

So, is it dry yet?

_________________
http://www.presnallguitars.com

I suppose its dry. It is certainly dry around the edges but it was the hidden encapsulated parts that I was curious about.