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Hello,

Unfortunately I’m still having some issues with hide glue. Let me explain my setup:

Glue:
- BT&C brand 192 gram glue
- Mix is 1.8oz water to 1oz glue
- Using the hold heet glue pot (auto temp)
- Heating parts using heat lamp to around 140 before glueup

Neck block:
- Mahogany
- Radius using radius jig I built recently. Perfect fit for the block before glueup

Here is my clamping setup for the blocks:


The clamping setup is a clamp caul on the sides exposed above the mold. I put a couple bits of router pad between the caul and the sides. The caul is clamped in place with bar clamps. A second set of bar clamps is put on the other side and clamped directly to the mold.

Basically like this:





I glued the blocks in and left them over night. Yesterday I drove the bus to radius the sides and noticed that the sides have pulled away from the block. Here is a video of me flexing it:

http://youtu.be/gQst0z4J7_s

I’m not even sure where to start troubleshooting but I have some suspicions:

1) Should I do away with heating the parts before glue up? Could that be causing an issue?

2) Should I perhaps wait just a few seconds after brushing the glue on before clamping up? I’m experiencing a lot of squeeze out and glue running during clamp up. Maybe waiting just a beat for the glue to thicken before trying to clamp up?

3) Could the bar clamps be starving the joint?

4) Maybe try a thicker glue ratio?

I read on here about people using rubbed joints for bridges for crying out loud and yet I’m struggling to get necks and tail blocks glued in correctly.

Brad


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HMMM!?!

Is your glue getting hard after it dries? Put some glue on a scrap of wood and let it dry, it should be hard and brittle.
Are the gluing surfaces freshly scraped before gluing?
Could there be sawdust or other contaminants on the gluing surfaces?
Is it your sense that the glue line never bonded, or do you think it may have broken along the joint when you were driving the bus?

I don't really have any idea what is going on here, I'm thinking out loud.

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Bryan Bear PMoMC

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I closely inspected the joint before driving the bus. I believe it pulled away while driving. The top is not radiused yet, only the back. The sides are pulling away from the block on both sides of the block and only on the “back end” of the block. The “top end” of the block is fine.

Both surfaces were recently sanded (not scraped though) and I didn’t wipe the rosewood before glueup (I’ve never done that, I’ve read mixed feedback on it). I wipe them with a shop towel before glueup to get any dust off.

I appreciate the thinking out loud with me on it. I’ll try the glue test to make sure it is hardening.





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To me it looks like a starved joint.

Are you applying with a glue bottle or a brush? I use a small glue that lives in my glue pot. I'm able to apply enough glue very quickly leaving only squeeze-out to deal with. The rest of your setup seems good to me.

Brad
I was taught to make “intimate contact” between glue surfaces the goal to achieve a good bond.
So I am looking for smooth surfaces to maximize contact on the glue surfaces. Is your caul on the outside of the ribs a very tight fit? If so you don’t need any padding between the caul and the ribs. Is the lack of bond where you used the additional caul? Again I’m just thinking out loud as to possibilities.


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For these blocks I applied with a bottle and then used silicon brushes to spread it out.

One thing that just occurred to me. The procedure I follow to clamp is this:

1) Glue applied to block and then placed in position. The soundboard side of the rims are on the table. The block gets put in and slide down so it’s flat against the table.

2) Clamp lightly with the bar clamps on the clamping caul on the “guitar back” side of the rims. The side that sticks above the mold.

3) Flip the mold on its side and clamp into the bench vise to secure it.

4) Clamp lightly with the bar clamps on the soundboard end of the block.

5) Tighten all four clamps.

What I noticed is that because I’m clamping on the “guitar back” side first, meaning the side where the rims stick up above the mold, it causes the end of the block that was initially against the bench to ramp up because of the pressure. Lots of glue runs out during this process.

Here is a somewhat exaggerated view of what I mean. The block is placed in position with the mold flat on the bench. The two clamps are put on the clamping caul side. The mold is then tipped up on its side and clamped into the bench vise. What I then see looks like this:



Then I add the second clamps:


Perhaps too much of the glue is escaping when the block is ramped up like that?

I do think I’m getting too much glue squeeze out. It’s hard to even call it squeeze out because it is more like running out.





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Is it possible doing this is wiping some glue off the lower part of the block and starving the joint?

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Thanks for thinking it through. The caul is a good fit for the blocks. They were made using the same template / jig.



For the sides they were sanded to 220. The block was only sanded to 80 coming off the disc sander. Would you take that to 220 as well? The surface looked pretty good off the sander, but of course it could be improved from 80 grit.


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For gluing blocks I like hide glue to be the consistency of molasses - thick enough to hold on long enough to put the block in place. For general use I fill a plastic bottle with the granules of hide glue and then fill the voids with water (just up to the top of the glue) I've never really measured it, and if I want it thicker I add more glue, thinner add more water.

Slide down might be the wrong term. For this I’m trying to indicate that the block is flat against the bench. So the soundboard side of the rims are pushed flat against the bench and when the block is installed it is also pushed flat against the bench. Hopefully that reads correctly.

Hope you had a great holiday, Colin!


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Hmm ... I try to ease all the clamps into compression relatively equally. (As you do when tightening the lug nuts when changing a tire.) I also use solid cork for padding on clamping cauls, so maybe there is something to the gaps in the padding you are using, I don't know.

That said, I would start by taking a look at the glue itself. I don't typically get a lot of glue running all over the place while I adjust the clamps--some, but not a lot--so maybe you had the glue too thin. The ratio you used is brought up often and I suspect it originates from Frank Ford's incredible and invaluable website, Frets.com. What I've yet to see anyone note is Frank's caveat that, "Every batch of hide glue has a different ideal mixing ratio and that's why I bought a fifty pound bag of the stuff so I'd never have to figure it out again!" What's "ideal" has to be determined for each batch.

I'd stop working on the guitar for a bit and do some testing of the glue, then I'd make solid padding for the cauls. Finally, I'd work out a way to tighten the clamps in a manner that applies even pressure throughout the process. If that doesn't fix it ...

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George :-)

Definitely keep heating the parts. Any movement after the glue gels will ruin the joint.

I think the problem is glue starvation, but not due to excessive clamping pressure. Sounds like your glue is on the thin side, and you're applying it to the block only. Most likely the glue is running while you get the block into position, leaving some thin film areas on the block, which don't have enough glue to wet the sides once you get the pieces together. Quickly squashing it with clamps also reduces the chance of proper wetting.

Brush glue onto both surfaces and it should work. Or use a thicker mix and rub it around as you squeeze the glue out, to spread glue onto the sides.

Any chance your silicone brush is chilling the HHG prior to closing the joint? If the silicone brush is cool, and large enough, it may chill the glue. I use my finger to gently spread HHG for most applications.

Wipe the sanded surfaces with naptha to remove any dust?

Other than that all your temps and ratios sound good - I would suspect a starved joint.

??????????????
Something fundamental is going on.
I've never had hide require heroics or be finicky.
Was the joint week and it came open, or was it strong but had a gap?
Do you know it was tight when u clamped it or could it have been rocked open as you described?
No waxed ends on the side set or other contamination?

I'm with George L. start with the glue working on scrap.

I typically put 25 grams of 192 in a jar and add 45 grams of water for total of 70.

painting both surfaces?

This brings up a good point. I would have suspected the time to brush glue on both sides would be too long. Maybe I need to rethink the amount of time I have.

If I take two non heated surfaces and spread glue on them with a brush, as a rule of thumb how much time can elapse before there is risk of the glue gelling up? Understood that each situation is different, but let’s assume room temp pieces. I would guess it would take 20 - 30 seconds to brush glue on both and get the surfaces together. What happens next? Should they be held in place with finger pressure until the glue grabs and then clamped up? Or will the clamping after the glue grabs cause the joint to move around slightly which would risk compromising the bond?

I guess to sum up... how much time do you typically have to get from brush to clamp before the glue has gelled and you risk ruining the bond?


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A good point on the brush - I actually keep it in the heating pot. What I do is take it out of the pot, dab on a paper towel to dry it, then into the glue.

Good point about Naptha, I haven’t been doing that but will start.

I do feel like the glue is too thin. I’m going to shoot another video to get some feedback on it.

Appreciate the help!

Brad


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There is NO way that you are starving the joints by over clamping. In fact, those quick clamps are likely not giving enough clamping pressure. I prefer iron clamps for this joint.

Honestly those Irwin grip clamps have really poor clamping pressure - they don't clamp that strongly to begin with, but as an added bonus they also loosen back. I don't believe this is glue starvation; rather insufficient clamping pressure. Hide glue is an emulsion in water. It will soak into the woods, and you obviously apply generously. For this kind of clamp up, my favorite clamps are Bessey screw clamps, with the rubber grip handles. They will provide excellent clamp pressure, stay where you put them, et cetera.

https://www.toolbarn.com/bessey-tg5-512-2k.html/ - this size is handy in the luthiery shop.

I have Irwin clamps, mind you. I use them for various light tasks or non-critical tasks. But generally they are a light duty or supporting clamp. With HHG I believe you will fare far better with a screw clamp.

For the end block (as I believe you are doing) 2 clamps top and 2 clamps bottom, using screw clamps, should provide the clamp pressure one desires across the end block.

Andy

I have a question based on these last two comments. Does hide glue require high clamping pressure to get a good joint? I haven't seen that come up in previous discussions about pros and cons of using hide glue.

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It sounds like the case is pretty strong for starved joint (assuming the glue tests show it is hardening properly -- I suspect it is since part of the joint is intact). I'll just throw out one more thing that probably isn't the problem. . . is your silicone brush brand new? I'm wondering if there could have been some residue from the release agent that may have contaminated the joint.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

This is a good question. I’m really very surprised to see two replies that indicate the clamping pressure was too light. I used four of the medium duty Irwin clamps.

Again, there are advocates here for rubbed bridge joints. How can four bar clamps not provide adequate pressure for a neck or tail block?

Mind you, I’m not discounting the advice, just trying to understand it.

Thanks!
Brad


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Not a new brush. It’s been in the rotation for a while. Interesting thought though. So many variables inside of such a simple operation.

Brad


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If your parts are heated you should have plenty of time. The time is somewhat mass dependent. A thin layer will quickly become the temp of the piece. I like a large brush that holds a good volume of glue. put on a little too much and remove excess with the brush. the big brush provides a bigger mass to keep things hot while your spreading.
You'd know if you didn't make it because the gelled glue is not very compressible so the joint will not close tightly. There will be a pad of glue in between. If you do crush the gelled glue closed, the squeeze-out is different. Not beads of liquid but textured. Like squeezed out jello.

I don't think cooling is your problem.

Use some scrap blocks and wait too long on purpose to see what it feels like. The pieces just keep sliding around. They never come all the way together and grab.

I don’t know if this helps or not, but this is the exact bottle of glue I used for this block. The piece of scrap is on an angle about 60 degrees.

http://youtu.be/ir1cNI492rE

I’ll do some tests on scrap. I guess I’ll also get to test out the steamer later.


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The pieces of router mat might have "released" and resulted in poor clamping pressure. Same thing happens with screw clamps on rubber hoses. After an initial snug fit, the rubber relaxes, and the clamping pressure lessens.

Alex

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