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What David and Grumpy said.

Good info, Todd. Your "CV" as well as your woodworking skills speak volumes and I always appreciate your backup when you make your well-conceived points.

BTW...I'm curious...what's your rationale for using 315g HHG on bridges...and how are you getting 3-4 minute open times? Also, what's the viscosity like for this stuff?

TIA

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

You guys made this a great thread!
Todd, I also would like to know your viscosity and your thinking on 315g HHG. I purchased mine from someone here on the OLF so I'm sure it's the "norm" for guitar making. I use 220 grit sandpaper on ebony. Actually I get it close then I lay sandpaper on my soundboard and without distorting or pushing down on the soundboard I sand the bridge to fit. I mix my HHG by wieght and it's usually 50%/50%. However it seems a bit thin according to from what I'm reading here. Clinton

If I had to guess, I'd say you're doing it right with maybe the exception of not getting all of the FP off of the top. When the bridge pulled, did it leave your HHG on the surface of the bridge or on the top of the guitar. If on the bridge, your top wasn't prepared well.

Todd:
Many thanks. I had read about surface energy in an Experimental Aircraft Association magazine a few years ago, and had, perhaps, been discounting the importance of 'keying' a bit too much. I generally use a freshly scraped bridge surface, and have had only one bridge come up; it was definitely a cold joint, though.

To explore another aspect: somebody mentioned wood type. I know some people feel that some 'oily' woods need a solvent wipe to get proper glue bond strength. I don't wipe down the glue surface, as I've heard conflicting reports. Some people say it just brings oils to the surface, and spreads them around, so that you end up with more problems. Any comments anybody?

Not to drag this thread away from proper gluing techniques, but are you absolutely sure that your string balls are seated and pulling on the bridge plate and not the bridge itself?

Coe

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Give me 50 cents worth of regular.
Check my oil too, if you don`t mind,,,

[QUOTE=ToddStock]

Also - I'm still playing around with ideal viscosity for the lining-to-top and back plate joint. For braces, etc., I mix at 1:1.8, but after skimming, it's probably down to 1:1.4 or less. Might see what the other guys are saying.
[/QUOTE]

Todd...I've been gluing down tops & backs with HHG for a few years...8 guitars. I've settled on a viscosity about the consistency of molasses. The 192g HHG runs out of a small Titebond bottle with the slit opening and forms a perfect bead on the lining...no running. I slap on the top and gobar it in place...all within 45 seconds. This is essentially Mario's method...thanks Grumpy!

On my next, however, I will be trying Fish Glue and plan to be able to liesurely drink a beer during the open time! So far, my testing of FG has yielded bond strengths every bit as good as HHG. I believe that Colin has also qualified it for his tops and backs.

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

Coe, I did think of that and checked, they were seated properly. Paul, 90% of the glue was left on the bridge,however I squezzed the glue directly onto the top and then placed my bridge,with no glue, on to the top. This sounds like it could be my problem. I didn't think of wiping down the bridge. If I use more water than glue weight ratio the glue is really thin. Where can I purchase 315g and I'll try that. Clinton

I don't know much about all of this, but it sounds to me like the top
was not completely scraped free of finish.  Also, I think the point was
to use less water than glue ratio vs more water, to get a thicker, more
gel like, product.  Note the ratios that Todd quoted.  I think he's talking about 1 part water to 1.8 parts glue.  Skim off leaving 1 part water and 1.4 parts glue.  Make sense?

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

If you squeezed your glue onto a cold surface (the top) and placed the warm bridge on top, it's one possible explanation as to why the dry glue adhered mostly to the bridge. Try heating both surfaces.

I don't ever wipe down wood before bonding...especially oily wood. But ebony isn't oily anyway. It's just a fresh scrape on each surface for me.

I don't think it's a gram strength issue. Thousands of luthiers use 192g and it is the standard. I'd recommend making sure you can make that work first...just my opinion. But I'd also make sure you have known fresh stuff and incorporate all the tricks that have been listed above regarding surface prep, temp., speed and clamping force.

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

[QUOTE=crich] Paul, 90% of the glue was left on the bridge, [/QUOTE]

That sounds like the bulk of your problem right there. When a bridge
comes off, you really shouldn't see much glue at all. A properly fit and
clamped bridge should have literally a microscopic, ideally single
molecular thickness layer of glue between the top and bridge. Hide glue
has very little gap filling strength. Ideal bonding really relies on individual
strands of collagens being in contact with both surfaces.

If I'm understanding you correctly that there was a visible glue layer in the
failed joints, you just need a better wood to wood fit. Causes could be
premature gelling of the glue, finish ledge around the perimeter holding
the bridge away from the top, or simply not enough clamping pressure.

For the first, like everyone I heat my surfaces before gluing. Thirty to
sixty seconds under a heat lamp for the bridge while I blow the top with a
low temp heat gun (hair dryer would work fine), is my method. Second
can be helped by rabbeting the bridge edge to lay over the finish,
allowing solid wood to wood contact with the bridge and top. Many folks
here do this, as well as some manufacturers like Collings. Third, just
make sure it's clamped firmly before the glue gels. While starved glue
joints can certainly be a concern with some glues, it would be pretty
tough to get one with a good mix of hide glue, if possible at all. Just don't
clamp so hard as to crush wood or pucker the finish too bad and you
should be fine.

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Eschew obfuscation, espouse elucidation.

Thanks guys, you're the best! Clinton