does liquid hide glue draw together like hot hide glue

[fazool]

I understand that hot hide glue can be assembled with very little clamping force. That the glue contracts as it hardens, drawing the parts together.


Does Titebond-type liquid hide glue do the same?


Is that contraction a side effect of heat or the glue curing ?

I don't think hot hide glue does that.

[Howard Klepper]

Originally Posted by fazool

I understand that hot hide glue can be assembled with very little clamping force. That the glue contracts as it hardens, drawing the parts together.


Does Titebond-type liquid hide glue do the same?


Is that contraction a side effect of heat or the glue curing ?

That is part of hide glue mythology that keeps growing as it is retold. I've even seen someone claim that you can unclamp a hot hide glue joint as soon as the glue jels (about 90 seconds) and the glue's miraculous self-clamping power will do the rest.

Any glue that cures by evaporation of a solvent or vehicle shrinks as it cures. Hide is not unique in this way. Because hide glue is especially bad at filling gaps, it is best with lots of clamping force. But all glues are best with more clamping force than is usually applied in small shops, with the possible exception of epoxy, and there it doesn't hurt to clamp hard even if it isn't necessary.

In fact, it is recommended that when using hide glue the clamps be tightened a couple of times as it cures, to compensate for any shrinkage.

[fazool]

Thanks Howard - I was buying into the mythology about HHG "self drawing".

I'm glad you cleared it up for me.

[redir]

http://www.frets.com/FretsPages/Luth.../hideglue.html

About the 7th paragraph down. Now granted he does say for joints where high strength is not necessary. I've read where some luthiers will just rub top plates together with HHG. Personally I clamp everything except perhaps cleats or something like that with CA and even then you 'clamp' it by holding it in place for 30 seconds.

[dekutree64]

Originally Posted by redir

http://www.frets.com/FretsPages/Luth.../hideglue.html

About the 7th paragraph down. Now granted he does say for joints where high strength is not necessary. I've read where some luthiers will just rub top plates together with HHG. Personally I clamp everything except perhaps cleats or something like that with CA and even then you 'clamp' it by holding it in place for 30 seconds.

For violin family instruments where the plate joining surface is large, a rub joint should work. Might work on thin guitar plates too, but I wouldn't try it. Tape joining is so easy, no reason not to use it unless you're just out of tape at the time

But I do rub joint bridges and haven't had a failure yet, even in really harsh humidity conditions that put even more stress on the joint. I did a headstock scarf joint without clamps a couple years ago as well, and it passed the test of me standing on it, and is still going strong.

I'm not sure if liquid hide glue would have similar magical abilities, but my gut says no. I think the gel action is part of what makes it work.

Also, keep in mind that it only works on perfectly fitted, stress-free joints. And even then, the water expansion of the wood from the glue can cause things to separate around the edges before the glue has time to dry.

[redir]

I just watched a couple of video's that showed the strength of rubbed joints. It looks pretty impressively strong.

https://www.youtube.com/watch?v=x-6BWTdRsw8

[Alan Carruth]

Howard Klepper wrote:
"Any glue that cures by evaporation of a solvent or vehicle shrinks as it cures. Hide is not unique in this way. Because hide glue is especially bad at filling gaps, it is best with lost of clamping force. "

I'll agree with Howard on the first part, but not the second: high clamping force (assuming he meant 'lots' rather than 'lost') is not needed with hot hide glue, and may not be with other glues, for that matter.

Joints assembled with wood glue tend to be strongest when there's between .002"-.006: of dried glue in the joint in the end. Too little glue raises the risk of a 'starved' joint, where there are areas with no glue at all. Too thick a glue line tends to be weak because most of the strength is in the chemical bond with the surface rather than the material itself. You want a lot of surface, and not too much glue.

Viewed this way, clamping force is simply the way you get the excess glue out of the joint. The amount of force required depends on the effort it will take to get the joint to end up at the correct thickness. If the parts fit well, and the glue is thin, you can easily end up with a starved joint using any clamping pressure. Similarly, in a 'rubbed' joint the excess glue is worked out by rubbing the pieces together, and any clamping after that would be not only superfluous, but probably harmful. There are cases where you may need to use high clamping pressure: pulling carcase parts into line when assembling a large furniture piece, for example. In that case you may well want to use a thicker glue mix to avoid any possibility of too much squeezeout in parts of the joint and starved areas.

I use rubbed joints using hide glue when joining plates for arched instruments; either guitars or fiddles. The keys are to make really flat surfaces, so that the glue line won't be out of spec, put in plenty of glue, so that you know there are no gaps, and to stop rubbing and align the parts before the glue gels. Then you just walk away.

What's happening here is that the gelled glue does have some minimal strength, which increases as it dries. This, and gravity, holds everything together during the drying process. It's surprising how fast the strength of the joint can be developed. In demonstrating a rubbed joint for a student once, I planed off a leftover piece of spruce brace stock flat, put on some glue, rubbed the pieces together, and put them down carefully. Fifteen minutes later, I clamped one side in the vice, hit the other with a hammer, and got 100% wood shear.

Note that once hide glue gels, that's the structure of the joint. Hide glue is like (heck, it is) gelatin: if you cut it apart after it gels the pieces won't stick together unless you heat them up and melt them again. I use rubbed joints on arched plates because the surfaces are wide enough and the pieces heavy enough that they won't fall apart from a slight breeze. I have heard of folks who use rubbed joints for Classical guitar top center seams, but that just doesn't seem stable enough for me to trust it. I don't doubt their word, I just don't feel I can do that safely.

I've never tried a rub joint with Titebond 1 wood glue. I see no reason why it would not work. Due to the nature of the suspension of the glue in water it may be less subject to starved joints than hot hide glue, and more tolerant of high clamping force.

As for liquid hide glue, such as Titebond or Frankilin's; the best advice is to avoid it. I don't know anybody who's used it for any length of time who has not had failures that simply would not have happened with regular hot glue, or yellow Titebond. It can work fine if you get a fresh bottle, but seems to go bad over time at an unpredictable rate.

[Howard Klepper]

Originally Posted by Alan Carruth

Joints assembled with wood glue tend to be strongest when there's between .002"-.006: of dried glue in the joint in the end. Too little glue raises the risk of a 'starved' joint, where there are areas with no glue at all.

Alan, I can find nothing in the published research that supports this claim. What I do find is that .002-.006" is what is commonly found as glue line thickness and what is often used as a standard in testing, and that these thicknesses are adequate, but the greatest strength in US Forest Products Lab testing was at the thin end (.002"). There was no minimal thickness mentioned in those tests where the strength of the joint diminished. E.g., http://ir.library.oregonstate.edu/xm...15B?sequence=1 (US Forest Products Laboratory, "Effect of Thickness of Glue Line on Strength and Durability of Glued Wood Joints," 1960) That test used glues then popular in commercial applications--HHG and ARG were not included. I also noted that they used a clamping pressure of 150 lb/sq. in. to achieve that. Most manufacturers (e.g., Franklin) recommend clamping hardwood joints with pressures exceeding 180 lb/sq. in. With ordinary wooodworkers clamps, that can barely be achieved if you placed clamps everywhere with no spacing between them and tightened hard.

Next, see this from Fine Woodworking: http://www.finewoodworking.com/item/...mping-pressure. They say .004" is a maximum for a strong joint and say nothing about a minimum. That article recommends 150lb./sq.in. for flatsawn pine, and far more for hardwoods, e.g., 1200 psi for flatsawn sugar maple! No way you will get that without specialized hydraulic presses that are way beyond the capabilities of small shops.

And here: http://www.finewoodworking.com/item/...ets-to-success --the editors of FW say that starving a joint from overclamping is a myth, citing Prof. Roman Rabiej: "In reality, Rabiej found that most woodworkers are underclamping their joints. While some woodworkers fear over-clamping could starve joints of glue--it’s a myth. You can almost never apply too much force using common woodworking clamps, Rabiej says."

If rub joints work well enough--and I use them for some applications, too--it is because the glues are good enough to be adequate without clamping in low stress joints. It's certainly not because thicker glue lines are better. So long as both surfaces are fully coated, I can see no reason why there would be any loss of strength with glue lines far thinner that we are capable of generating with our best jointing and maximal clamping abilities.

To those citing Frank Ford: yes, he says that rub joints will often work with hide glue and that it draws the surfaces together as it dries. He does not say it is unique in this property (it isn't) and he does not say that a rub joint is just as strong as a clamped one (it isn't). But I think his piece about hide glue may, by being misread to be saying more than it actually does, be the source of the myth among luthiers that hide glue requires little if any clamping. You often can get away with that; you will not get the strongest joint that way.

Violin makers intentionally weaken some joints (plate to ribs) to make disassembly easier. I don't think there are any joints on a guitar that benefit from being intentionally weakened. We don't take them apart nearly as often as violins are taken apart, or for the same reasons, and have methods for releasing the glue when we need to.

[murrmac123]

Originally Posted by Howard Klepper

... While some woodworkers fear over-clamping could starve joints of glue--it’s a myth. You can almost never apply too much force using common woodworking clamps ...

God only knows where the myth originated from ... none of the craftsmen I worked with and learned from 50 years ago ever spouted this nonsense ...I suspect the internet is to blame...

[Dan Carey]

I'm far from an expert on the subject (I'm about to use hot hide glue for the first time on a fiddle that I'm building). During my reading...LOTS or reading during the past couple of months...the general opinion of the pre-mixed cold hide glues is not very high. Folks say that it's easy to use but that it tends to creep quite a bit after a while. Read the customer reviews on the Stew Mac website and search for some other opinions on the pre-mix. I decided on the hot version.

I'll let you know how it works!

[fazool]

oops undeletable repeat post....nothing to see here....move along

[redir]

Yes Franklins liquid hide glue is generally considered not suitable for instrument making. I used it on my very first classical guitar about 25 years ago because I was simply ignorant. I will say however that this guitar is still functional today but there are many many horror stories of others using it, so don't be tempted, it has none of the properties that make HHG so desirable in the first place.

[Viking]

Originally Posted by Alan Carruth

...

Originally Posted by Howard Klepper

...

Interesting to find conflicting points of view on this subject... glue starved joints. I've read about starving a joint of glue a number of times here on the forums. It's influenced my thinking some as I am learning how to build guitars. Is it really not an issue? Has anyone around here ever had a joint fail due to insufficient glue?

[Ned Milburn]

Originally Posted by Viking

Interesting to find conflicting points of view on this subject... glue starved joints. I've read about starving a joint of glue a number of times here on the forums. It's influenced my thinking some as I am learning how to build guitars. Is it really not an issue? Has anyone around here ever had a joint fail due to insufficient glue?

It is possible to starve joints of soundboard braces by putting too much pressure in the clamps. Larger surfaces will be difficult to starve of glue (ie: fingerboards).