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It's a long shot, but can anyone give me an idea how long hide glue takes to crystallize?
I've just hide glued (192g strength) an extra brace on the back of an assembled guitar, but judging by the frequency response (it's only showing a lower frequency) the glue has not crystallized, and the only effect I am getting is from it's weight, not additional stiffness.
An internet search with various terms throws up nothing!
If no-one can help, maybe I can let others know how long it takes until it hardens fully.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Keep in mind that a properly glued joint has very little glue in the joint. Hide glue hardens fully in about 24 hours.

How can you be sure you're only seeing the weight, and not the stiffness?
Isn't it possible that the total effect is a lower frequency? If the change in mass is more significant(for lack of a better word) than the change in stiffness, wouldn't the result be a lower frequency?

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A man hears what he wants to hear, and disreguards the rest. Paul Simon

Yesterday I glued a Classical bridge with old Hide Glue. No clamps, just a very quick rubbed joint. There was even a bit of mould on the surface of the glue (I did scoop that bit off).
6 hours after gluing it was strung to full tension. Not that I suggest you follow this procedure. It's still appears to be fine today. Hard to believe but true.

Hi Michael - In Europe some folks call what we call "pearl glue" "hot hide glue" so I just want to be sure that we are speaking of the same thing.

It's not uncommon for classical builders to use a rub joint with great success. Steel string guitars have more tension and as such we want a perfect fit, as much wood-to-wood gluing surface as possible, and proper clampage. I will at times remove the clamps from a bridge after 4 hours but I never stress the bridge until 24 hours have passed AND this is with proper temperature regulation as well so the that the glue can cure.

We also won't use the glue instead pitching it if we see mold.

Interestingly I have had to remove a HHG glued bridge a day later, 24ish hours later, and the glue around the perimeter had cured but glue inset a bit was still tacky.... This tells me that for larger surfaces more time might be prudent.

Sorry, I don't think a 12" long, 1/4" wide, 1/2" high spruce brace across a back between the 2 main braces will show more weight than stiffness. That's only a few inches shorter than the size of my parlor X braces!
I think the glue is still in a gel state, and the vibration is not being transferred significantly between the plate and the brace (for want of a more technical phase - Edit - coupling?) - I tried 1 hour after gluing (I know it's too soon), and now again after another 3 hrs - back frequency dropped about 2 Hz initially, and now going up a bit, (about 1 Hz so far)
I'm pretty sure I have the back peak at 213.6 Hz because with a weight I lowered the frequency of the back to 207 Hz and the top went from 183.6 Hz to 180(ish) Hz and body went from 100.6 to about 99.6 Hz (edited frequencies - was tired!)- frequencies responded much as expected with a live back.
I'll see how it looks in the morning.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

213.6 is an excellent peak. It's pretty much ideal, why are you trying to change it?

I want to drop the top peak (still at 183.6 Hz, close to F sharp) and the side mass is getting hefty at nearly 22 oz (starting to feel like lifting a double bass) - I am thinking to sand the bracing a little, but weighting the top indicates the back and body will drop more than I would like anyway.
Taking the back frequency up will allow me to lower the top Hz without having so much impact on the body Hz (insert "head hurts" Smilie)

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Well, I'm not near my electro gadge to tell me what the cents are, but I personally worry the very least about main air (because it's so much harder to control than main top/back). I've even had near perfect octaves between air and top and had it sound just fine. Even went through the effort of retrofitting a sound port to raise main air, and no real audible difference.

Point being, I would leave back at 213.6, and gently plane the top bracing down to 180. If it made even a 1/4hz difference to main back or main air I'd be surprised...

.02

It was HHG and Pearl Glue, a mixture. Sometimes known as Cologne glue. Probably sat 2 weeks in a jar, out in the open.
The fact that it was a Classical bridge is irrelevant. We need good joints as well. I've glued Lute bridges on with nothing more than light finger pressure, not even a rubbed joint. Large Lutes can reach steel string tension (60Kg+) with virtually half the bridge footprint of a SS Guitar. Good joints, yes. Clamps? Not necessary.
I looked at the Guitar this morning and it's still fine!

Good joints always - agreed.

Many steel string builders dome our tops and as such I would never attempt to glue a bridge on a steel string without clamps. For classicals the top is flat. This and the lower tension of the stings is likely why you guys can get away without clamps.

In repair work all bets are off and rub joints won't cut it. Tops distort over time and no longer have a consistent dome or are consistently flat making clamping a must as well.

I'm very aware of the rub joint practice and even not using a rub joint. I also know that bridges lift - it's what pays the bills these days. YMMV

Hesh. Very few Classical Guitars are built flat. They haven't been building them flat since about 1870 and Torres (although he certainly wasn't the first).
It's nothing to do with domed Tops or lower string tension, hence my point on the Lute. I didn't invent the idea of gluing on a Lute bridge with light finger pressure. I got the idea from a Lute maker who has been in the business since the early '70's. Rubbed joints work and have a long history of working. I haven't used a clamp on a bridge for over 7 years!
The reason I used old glue was because the instrument was about to be crushed (by me). It had been hung on the workshop wall for nearly 3 years. Far too many niggling mistakes. I found the bridge that I had made for it and determined that it was worth the 3 hours work to finish it, just to see what it sounded like. I had no glue ready. I didn't even freshen the surface of the 3 year old Bridge or the 3 year old soundboard for that matter. It took me less than 30 seconds to determine the correct bridge position. It took less than 15 seconds to glue the bridge. 6 hours after gluing the bridge it was at 40 Kg string tension.

Sorry, I don't believe your premise that the brace is not vibrating with the back because of uncured glue. I believe any increase in frequency during the drying process is because water has left the wood, reducing the mass.
Whether braces add more stiffness than mass is purely a function of their stiffness....which is mainly driven by the height. If the brace you added was no taller than the other braces, it would not surprise me if the frequency went down insted of up.

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John

John, you may well be correct. That did occur to me last night after posting, but such a small amount of glue, only half of which is water??
Either way, frequency of the back was up this morning from the original 212.6 to 214.3 Hz. (frequencies were 100.9, 184.4 and 214.3 Hz)
Shaved the braces, ended up 99.7, 180.0 and 214.0 Hz.
Spectrogram (strings on and damped) looks not bad, and the guitar sounds more balanced around the F sharp (which was sounded especially dull on the 6th string, annoying!)

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Seems to me you pretty much nailed it.

24 hours is plenty for hide glue as long as it hasn't been spreader on too thick and the brace was clamped properly


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