fiddler135 - Posted - 05/31/2022:  13:59:46

I have a question about hide glue. Can you trust a joint if the glue is exceptionally thin?
I joined two halves of a maple back day before yesterday. The glue was almost thin as water, but the joint seems ok. I haven’t stressed it excessively however.
Today I was gluing a rib to a corner block. The joint came apart, twice, two tries, and the surfaces were wet, but not sticky. Normally the grip strength holds here.
Can I trust the maple joint?

Brian Wood - Posted - 05/31/2022:  14:41:54

In my experience the glue needs some viscosity to be strong. Thin as water might be too thin. You should try to stress the joint now. If it holds up it might be okay. If it doesn't it's better to know now.

fiddler135 - Posted - 05/31/2022:  15:04:41

I stressed the joint (again); and this time I really stressed it (as much as I dared to). I didn’t put all of my 225 lbs on it, but nearly so, with the center joint resting on the edge of my workbench. (A destructive test would defeat the purpose.)
I too supposed that hide glue got weaker with thinning, which is logical, but does the glue get weaker, or are the particles of glue just more spread out? That is, are there just less particles of glue in thin glue?

Brian Wood - Posted - 05/31/2022:  15:47:09

quote:

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Originally posted by fiddler135

I stressed the joint (again); and this time I really stressed it (as much as I dared to). I didn’t put all of my 225 lbs on it, but nearly so, with the center joint resting on the edge of my workbench. (A destructive test would defeat the purpose.)

I too supposed that hide glue got weaker with thinning, which is logical, but does the glue get weaker, or are the particles of glue just more spread out? That is, are there just less particles of glue in thin glue?

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I think the answer would be yes, there is less substance in the thin glue to begin with, and more water which when it is gone will leave a weak joint. Too thick of glue will leave a visible line which is  not desirable either. For me a good glue is more like warm maple syrup, but not watery. The trouble with testing your joint now is that it's probably around 3/4" thick on the joint. Overall it has plenty of holding power. But when you carve it down you will be relying on about 1/10" to hold the halves together and if any of it is weak you'll have a problem.

Brian Wood - Posted - 05/31/2022:  15:58:59

Another thing, did you clamp the joint? Tightly clamping it might have forced out more of the glue, which being so thin might not be good. If you did a rub joint did you feel it grab? That would be better.

fiddler135 - Posted - 05/31/2022:  16:13:48

quote:

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Originally posted by fiddler135

I stressed the joint (again); and this time I really stressed it (as much as I dared to). I didn’t put all of my 225 lbs on it, but nearly so, with the center joint resting on the edge of my workbench. (A destructive test would defeat the purpose.)

I too supposed that hide glue got weaker with thinning, which is logical, but does the glue get weaker, or are the particles of glue just more spread out? That is, are there just less particles of glue in thin glue? What I mean is, that with a good fit between parts, a minimum of glue is desirable, just enough to wet each surface with glue. If the fit is not perfect, you need some fill, even if it is a small amount. So a center seam may be fine with watery glue, but a rib to corner block needs more glue? I am just thinking out loud. Does this make sense to you (y'all)?

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fiddler135 - Posted - 05/31/2022:  16:21:05

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Originally posted by Brian Wood

Another thing, did you clamp the joint? Tightly clamping it might have forced out more of the glue, which being so thin might not be good. If you did a rub joint did you feel it grab? That would be better.

 

I didn't clamp. it grabbed. In fact I couldn't move it when I set one half on the other. There was a suction there, that felt like the glue grabbed, so I didn't force it. (I suppose I could have moved it if I tried hard enough.) 

KCFiddles - Posted - 05/31/2022:  18:03:12

I've got a critical joint to make today, so I'm making up a fresh batch of glue, a small batch. One tablespoon of dry glue to two tablespoons of water. I let it soak all morning, then heat it to 140F. That's the right consistency for best adhesion. For weaker joints, like assembling a violin, I'll thin it down. It's not uncommon to do a "rubbed joint" on plates. The joint should fit perfectly, and be warm, but usually you can just brush both sides of the joint, rub them together fairly quickly, and they will grab pretty well. Usually if you just leave them standing on edge in a vise, they will bond just fine. Over-clamping a hide glue joint, or using too-thin glue would make me nervous.

fiddler135 - Posted - 05/31/2022:  19:41:40

quote:

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Originally posted by KCFiddles

I've got a critical joint to make today, so I'm making up a fresh batch of glue, a small batch. One tablespoon of dry glue to two tablespoons of water. I let it soak all morning, then heat it to 140F. That's the right consistency for best adhesion. For weaker joints, like assembling a violin, I'll thin it down. It's not uncommon to do a "rubbed joint" on plates. The joint should fit perfectly, and be warm, but usually you can just brush both sides of the joint, rub them together fairly quickly, and they will grab pretty well. Usually if you just leave them standing on edge in a vise, they will bond just fine. Over-clamping a hide glue joint, or using too-thin glue would make me nervous.

thin glue made me nervous also. 

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TPJ54 - Posted - 05/31/2022:  20:19:13

I have reheated glue before and it was thinner than original. I think it has to do with hide glue shrinkage leaving it to seem watery.

KCFiddles - Posted - 05/31/2022:  21:02:41

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Originally posted by TPJ54

I have reheated glue before and it was thinner than original. I think it has to do with hide glue shrinkage leaving it to seem watery.

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I've had a glue pot going every day of the week for the past 12 years, at least. It does deteriorate with age, but I haven't noticed it thinning over time. I usually gets thicker due to evaporative loss of water, and needs a little water added, IME. That's why I make up small batches, and make up a new fresh batch whenever I have a critical joint, in this case a broken scroll/pegbox that has to be perfect and permanent.

The Violin Beautiful - Posted - 06/01/2022:  10:13:04

If you’re nervous that the joint isn’t strong, it’s better to redo it now than to finish a violin and have it come apart in someone’s hands down the road. No one will hold it against you if you redo the joint to improve it during the making process, but it’ll make you look pretty bad if your violin falls apart later, and it’ll be a major headache for you to have to repair it free of charge and for the owner to have to wait without the instrument while you repair it. The best advice I could give is to think about whether what you’re doing is good enough for the next hundred years, not just good enough for now.

For joining plates, use fresh glue. It shouldn’t so thick that it feels gloppy, but I definitely wouldn’t want it to be watery. Since the center seam is such a critical joint, it’s worth it to do a test run and glue something else. Once it’s dry, you can see how much force it takes to break and whether the break happens at the glue line or around it—if it’s the latter, your glue is strong.

fiddler135 - Posted - 06/23/2022:  03:45:44

Update; The two piece maple back center joint with thin glue revealed itself on the drill press drilling guide holes for the arching. I was drilling a hole at the centerline and heard a pop, stressed the joint and it came apart, clean. It re-glued back together without problem.

kjb - Posted - 06/23/2022:  08:29:21

if you follow the protocol its the best glue by a long shot.

fiddler135 - Posted - 06/23/2022:  10:08:02

? Please explain

fiddler135 - Posted - 06/24/2022:  04:04:04

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Originally posted by kjb

if you follow the protocol its the best glue by a long shot.

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Are you just bragging on the benefits of hide glue in general or is your statement specific to this topic?

The Violin Beautiful - Posted - 06/24/2022:  11:03:15

I don’t see how the comment ISN’T relevant to the discussion. Hide glue has been an unbeatable adhesive for millennia, certainly since the violin came into being. Although there is a small number of makers who advocate the use of something else for back center seams, the overwhelming majority of makers use hide glue for this purpose, and it’s not by chance. Hide glue (when prepared properly) has incredible strength and resilience, cleans up easily, can be reversed easily, costs very little, and avoids the major issue that many alternative glues face over time: creep. If the seam ever opens up, it’s a much easier job to deal with hide glue.

pete_fiddle - Posted - 06/24/2022:  11:16:42

Best thing about hide glue.... IM,"Very",HO.....  Is that it lets go gradually,  and re-sets, letting a well made violin or fiddle reach it's final comfortable equilibrium over time, and in a given environment without too much stressing or cracking of the wood.

Brian Wood - Posted - 06/24/2022:  12:54:11

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Originally posted by pete_fiddle

Best thing about hide glue.... IM,"Very",HO.....  Is that it lets go gradually,  and re-sets, letting a well made violin or fiddle reach it's final comfortable equilibrium over time, and in a given environment without too much stressing or cracking of the wood.

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Really? I don't think hide glue acts that way. A good joint doesn't have "creep", and when a joint lets go for any reason it breaks apart and doesn't reset.

pete_fiddle - Posted - 06/24/2022:  14:37:41

Hide glue reacts with moisture and temperature doesn't it? And a well made joint won't have too much tension that it needs to break apart in within its given perameters. But that's just my take on it, yours is obviously different.

Brian Wood - Posted - 06/24/2022:  15:27:11

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Originally posted by pete_fiddle

Hide glue reacts with moisture and temperature doesn't it? And a well made joint won't have too much tension that it needs to break apart in within its given perameters. But that's just my take on it, yours is obviously different.

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One great advantage of hide glue is that it CAN be reset with a little heat and moisture and new glue. Most other glues can't be reconstituted and won't bond with themselves. Cleaning out and repairing a hide glued joint is much easier than other kinds of glue joints. Where I differ with you is I don't think hide glue moves and settles as a new instrument ages. When wood moves enough a joint fails. I think it's pretty brittle, not elastic. When I remove a top or something like that it gives all at once with a crack. In hot humid climates it could be different. I know glue failures are more likely in those conditions and it's possible what you're talking about happens to some degree.

fiddler135 - Posted - 07/06/2022:  19:08:03

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Originally posted by The Violin Beautiful

I don’t see how the comment ISN’T relevant to the discussion. Hide glue has been an unbeatable adhesive for millennia, certainly since the violin came into being. Although there is a small number of makers who advocate the use of something else for back center seams, the overwhelming majority of makers use hide glue for this purpose, and it’s not by chance. Hide glue (when prepared properly) has incredible strength and resilience, cleans up easily, can be reversed easily, costs very little, and avoids the major issue that many alternative glues face over time: creep. If the seam ever opens up, it’s a much easier job to deal with hide glue.

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Playing the devil's advocate, if I had been using tight bond, or any other easy to use glue, the joint would not have failed, at least not so easily. But, since it did (and the glue was thin), the joint came apart clean. Then the joint went back together simply by covering both surfaces with fresh glue and realigning the parts, and no clamping. That could not be done with any other glue, but as I already said the joint probably would not fail with an "easy to use" glue. I think the real advantage of using hide glue for a center seam is that you can get a seamless joint with hide glue. With other glues you can't. 

kjb - Posted - 07/08/2022:  04:51:51

also you can take them apart with little or no damage, which is important for something that can last hundreds of years