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I keep trying to get that perfect hhg test on spruce, with full nasty ugly wood failure (like i get with fish glue) but NO. It works rather well with hardwood but not with spruce. I made a zillion tests and every time I mostly get a clean joint separation. Some fibers do rip out but nothing serious.
I wonder if my test "procedure" is wrong. I work a sharp chisel in the joint, lift and pop off the brace. We are talking very small classical guitar braces.

I should be confident my hhg setup is ok?

-40% rh
-i mix 1 parts glue to 1.8 water. Let it soak for 1 hour or so then heat it up. In use the glue runs off the brush in a string.
- Herdim glue pot
-glue temperature 145, definitely never outside 140-150, submersible certified thermometer in the glue.
-linden bast brush
-spruce pieces planed just before the glueup
-high room temperature (its summer, nearly 80 at times)
-pieces preheated on a clothes iron
-from pot to join-up, only a couple seconds. I press with my fingers for a while then put some gobars. Also tried rubbed joints. Tried to separate after 2 hours, and after 12, it is the very same every time.

Perhaps it is simply expected for the joint to break that cleanly when started with a chisel. Maybe they would not be able to put violins apart otherwise. I know how a fish glue joint behaves and trust me I wouldn't want to try dry-open up a fish glue violin. Or perhaps my glue is bad? Hide glue from dick.biz, they emailed back said it is about 240 in strength. Looks OK, not pearls not anything suspicious. Amber color, very little smell and nothing obnoxious.

Thanks...

Normally I would just shut up and keep trying at it, but I was getting confident lately and just put a set of braces on my current top build using hhg. With the remaining glue I attached some scrap. Other than that, the top feels fine. Sorry for the long blabla hope it makes some sense...

Thanks again.

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Build log

I don't try and separate the joint , you flex the joint and let it split at the weakest point.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Thank you John. I will definitely try that, making a test more similar to the real deal: large spruce plate and braces, then flex. I was using the chisel because my tests were on rather small scrap pieces.

On another forum someone suggested I might be starving the joint. I am starting to believe I was exaggerating with the anti-gel precautions. Hot wood, ultra quick and strong clamp.... He said he is brushing the glue, waits a moment, brushes some more, and then when pressing the thing down uses gentle pressure. When doing a bridge, he brushes the glue, gently presses the bridge down, pulls it off and adds more glue.

One thing I will try to give some serious flexing to the braces on my top once I finish carving them.

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Build log

Alex...one of the things I really like about using HHG is the idea of rubbing the joint. With braces, for example, I rub the glue-laden brace until it grabs. Once that happens and it doesn't slide around anymore, I lightly clamp with 3 gobars and let them sit for 4 hours. At that point, it only needs enough clamping force to assume the radius. In cases where I have had to remove a brace, I just plane it down and chisel off the rest after softening it up with a SMALL amount of warm water on a sponge.

In my testing, I have never seen any adhesion differences between FG and HHG. BTW...I use the 192 gram High Clarity HHG from M&H.

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

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Thanks everyone for the comments!

Since this morning I did some 10 or more tests and it is getting better. No wood heating, nu rush, no strong quick pressure. Brush first piece, dip for more glue, brush the second, add some more glue on the first then gently attaching them. Now on most cases I get a much more severe wood failure, although here and there the joint separates cleanly as before.

I don't know what is the real ratio during use. I constantly add some water, otherwise in a few hours it turns into honey because of evaporation. I tried to have it run off the brush like oil or syrup, not watery.


I suppose I will not replace braces on my top even if hypothetically they could be starved. The side walls are well covered with a thick glassy layer of squeeze out and all feathered ends have a drop of glue on them. I flexed the top quite hard (10x harder than it will ever see as a guitar unless someone steps on it ) and passed ok. I will stress it again in 1 month or so before closing the box.

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Build log

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Tony,

I am afraid I am not the best reviewer for the glue pot since I didn't use any other before.
But, it feels sturdy and well constructed. It is heavy enough, and the antislip rubber base works.

The inner pot is made of copper, i suspect that is safe to draw water from?

The ceramic pot is of a manageable size, a bit larger than a big cup of coffee, flares up to a max diameter of 10 cm.

I like that it has a dial. I fiddle with it often, because otherwise I found that the glue temperature varies. In general I keep the dial between 70 and 80 degrees, trying to read 60-62 on the glue thermometer.

It is pricey but it is nicer than those plastic thingies...

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Build log

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Update:

Today I received a new batch of glue, same SKU. Prep as before (1 to 1.8) the only difference was that this time I soaked it for more like 4 hours instead of the usual 1, simply because I received an unexpected visit) then glued several test pieces.
I instantly felt a difference: more tack when positioning and pressing the pieces. Not just my imagination, there is a difference. It definitly grabs and bites better than previous batch. And perhaps not unexpected, all break tests look better....

I should probably chisel the braces off...

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Build log

I don't/didn't know if this "does" anything but I usually let mine soak overnight before cooking it. My reason is partly because I'm lazy, and partly because I've got a small shop. I'm apt to knock the soaking glue off the bench while I'm working on something else. I was taught 30 or more years ago to mix equal parts of glue and water, by volume. That works out to approx 1 to 1.8 by weight. I've been weighing mine to that ratio for a few years.

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I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

Alexandru,

I wonder if 12 hours drying time is too short. I would give 24 if it was me.

Pat

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formerly known around here as burbank
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http://www.patfosterguitars.com

The time issue is a valid one. However, even the slow fish glue creates a joint stronger than wood in 2 hours. I did 2h fish glue tests in parallel and it seems to be nearly impossible to open the joint.

With this glue, the equal volume measurement gives different weights, the ratio being 1 to 1.4. It is rather finely ground, imagine rice broken in 3 or 4 pieces.

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Build log

That's why I started weighing mine a couple years ago. I normally use behlens and it's ground pretty course. More air space, less weight per equal volume. I like mine pretty wattery.

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I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

http://www.violins.ca/info/hide_glue_preparation.html
There are some interesting caveats regarding cleanliness in the paragraphs near the end of this article.

Back to the original post........ I was thinking about this. I use a cloths iron sometimes for removing and dis assembling stuff. I wonder if heating the pieces with an iron actually overheated the glue. When gluing top braces I normally aim a heat lamp at the top, making it 100F or so, and I lay the braces on my bending blanket, with the thermostat set to keep it at 100F. I've got a LOOOOOOOONG time to glue stuff that way, but it's not overheating the glue.

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I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

Npalen, thanks, interesting read. Seems to advocate a higher temperature, 70 Celsius? On my end, I don't think cleanlines was an issue. I do carefully wash the pot and the brushes in hot water (my tap runs to about 150 F).

Woody, yes, I remember the plate was pretty hot, and it is possible some strength might have been lost because of this, but maybe not an important lot. I remember reading hide glue will lose about 10% strength if cooked for 1 hour at 75 Celsius (167 F)

I would be really curious to hear what other people get when replicating my test. Spruce top offcuts are great for this. Plane/sand one clean, split a 1/4" stripe and glue it. Best would be to remove the squeeze out which otherwise strengthens the joint. There seems to be an interval after 2 to 3 hours when the squeeze out can be peeled with the greatest ease. Sooner, you smear it all over, make a mess and force water in the spruce and can get fibers pull out. After 3 hours it gets too hard to peel...
And then, after 2 to 4 hours, open the joint with a sharp chisel and after the brace has lifted, try to pry it off completely

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Build log

Well I was in the shop all day shaping necks and saw a soundboard cuttoff lying around so I decided to replicate your test. I used 192 M&H high clarity HHG.

I got interested when you said:


In my case the squeeze-out cleans best after about 10 or 15 minutes, after 2 or 3 hours its too hard. I include a picture of a test strip of glue after two hours you can get an idea of the hardness by the dust from the rasp.




Anyway, after 3 to 4 hours I tried to pry up the glued piece. It was stubborn and the blade wouldn't follow the glue line. I finally decided to pull it up with some pliers, I had to pull very hard before it finally broke, mostly along the glue line but pulling fibers from the soundboard piece. I also did a smaller piece, it behaved similar. I don't know what to conclude really, except that I'm satisfied with the strength of the joint. The last picture shows the two pulled off pieces turned up with the joint side showing next to the spot they were pulled from.

Thanks a very much lot! Looks satisfactory and very similar to what I get with the second glue batch.

My bad on the squeeze out. The one that peeled off nicely later was a very substantial patch left over by the brace. I really need some much smaller brushes! After 2 hours was still jelly like and I could pull it off along the entire length without ripping. Otherwise it does hardens must faster indeed.

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Build log