Failed Center Joint

[Jay Higgs]

I have never had a center joint fail before, but I also have never made a cello.  I jointed a cello back last fall, and left it in my shop over the winter (not too severe in San Antonio).  It was a hide glue rub joint supported by gentle clamping.  I had stored the wood for several years before using it.   As you can see, the center joint remains quite nice (second pic) except at the end, where it has split.  I suspect the ends dried out relative to the middle and contracted, splitting the joint.  In retrospect, I think I should have painted or waxed the ends while it was in storage.  Has this happened to any of you?  Would you try to crack the joint open or re-saw it?  I am leaning toward the latter.  Fortunately, I think I have enough extra wood to allow jointing it again.  

[Jay Higgs]

Addendum:  I decided to at least try cracking the joint with a wedge, starting at the failed end.  The good news is that it cracked clean and I haven't lost much wood at all.  The bad news is that it cracked so easily.  I used fresh Amanosan 3-B with controlled temp, which has worked well for me, and none of the other violin backs I jointed at the same time have failed.  I did glue-size the joint before the rub joint.  Maybe my clamping was more than gentle, and I starved the joint.  I mix my glue so that it is thick but still rubs to the point of a grip.  Any other thoughts?  

[fiddlecollector]

I would have used a higher bloom strength glue for a cello back joint, most seem to use 190 or higher . 140 may be ok for glue the plates to the ribs. Did you use a perfectly flat straight joint or slight hollowing?

[Jay Higgs]

Thank you for your perspective, fiddlecollector.  I plane the surface minimally concave, then after glue sizing I give it a fine shaving once more before gluing.  Davide Sora says he makes it concave just enough to see a trace of light through the center, and if I recall correctly, he doesn't glue-size.  I will probably try that.  My understanding is that Bloom strength does not equal joint strength.  It is a measure of the surface stiffness of the gelatinous stage.  Higher bloom strength comes from longer collagen fibrils, which penetrate the wood less.  I am using Amasonan 3-B, bloom strength 140 as you point out.  They make 001S and 002SB which have bloom strengths of 340 and 250, which I understand they recommend only for surface hardening such as in the guilding process.  Having said that, in the many old posts I have read, I see some of the pros using bloom strengths in those high ranges.  I have some 2-B (Bloom 250) that I have not used; I may do some experiments with that.   Your bloom strength of 190 seems like a good range; where do you purchase it?  

[Jeffrey Holmes]

Hi Jay; Not sure where fiddlecollector gets his (I believe he's in Europe, so maybe not where we can?), but 192 and 251 (from both Bjorn Industries and Milligan & Higgins) is distributed in the states. I like the high clarity type. You may have to search around a bit for a vendor who sells smaller than industrial quantities, but I've included a link for one who seems to stock it. Link

For what it's worth, I did test the Amanosan 3-B on (much shorter than a violin or cello plate) straight joints in maple (ala Christian Schabbon; tests on his website) when I first got my hands on it and found the bond strength quite impressive...  I did not size the joints, nor have I joined a back with it.

 

[Jay Higgs]

Thanks Jeffrey!  I just ordered the 192.  --Jay

[fiddlecollector]

I had never heard of that hide glue. It is probably just a mixture of sitting around in storage and your climate like you hinted at ,i believe San Antonio is in Texas ,if so then a complete difference in climate to me as i live in probably the wettest part of England. I have a cello back joined like yours in storage and i wouldnt be surprised if the joint in it has gone the same way  but i havent looked at it for years..

I always had a problem of getting cello backs and fronts joined before gelling due to low temperature climate.

I think also its simply due to the size of cello plates compared to violins, alot bigger and probably more movement with climate changes.

[David Burgess]

31 minutes ago, fiddlecollector said:

I always had a problem of getting cello backs and fronts joined before gelling due to low temperature climate.

One can temporarily produce almost any climate desired for gluing operations, without much expense or trouble.

[Jay Higgs]

I set up three violin backs at the same time as the cello back.  I just tested chips from all three, and none broke on the joint line.  I will paint the end grains anyway, as they will be in storage for a long time before I use them.  

1 hour ago, David Burgess said:

One can temporarily produce almost any climate desired for gluing operations, without much expense or trouble.

Right now in San Antonio I just turn off the AC in my shop. 

[Davide Sora]

4 hours ago, fiddlecollector said:

I would have used a higher bloom strength glue for a cello back joint, most seem to use 190 or higher . 140 may be ok for glue the plates to the ribs. Did you use a perfectly flat straight joint or slight hollowing?

4 hours ago, Jay Higgs said:

Thank you for your perspective, fiddlecollector.  I plane the surface minimally concave, then after glue sizing I give it a fine shaving once more before gluing.  Davide Sora says he makes it concave just enough to see a trace of light through the center, and if I recall correctly, he doesn't glue-size.  I will probably try that.  My understanding is that Bloom strength does not equal joint strength.  It is a measure of the surface stiffness of the gelatinous stage.  Higher bloom strength comes from longer collagen fibrils, which penetrate the wood less.  I am using Amasonan 3-B, bloom strength 140 as you point out.  They make 001S and 002SB which have bloom strengths of 340 and 250, which I understand they recommend only for surface hardening such as in the guilding process.  Having said that, in the many old posts I have read, I see some of the pros using bloom strengths in those high ranges.  I have some 2-B (Bloom 250) that I have not used; I may do some experiments with that.   Your bloom strength of 190 seems like a good range; where do you purchase it?  

I agree with fiddlecollector, I am one of those who use glue with bloom strength 315/350. The high bloom strength should also indicate that the protein chains are longer than with lower grades, so I prefer to use that for important structural gluing. I am using Nikawa (Amanosan), and recently I got some Bjorn 315 High clarity that I will try when I run out of Nikawa (I have little left).

How old was the wood you used? The large size of the cello amplifies the movements and forces at play, and the potential problems that may arise. With the same gluing, a violin joint might hold while a cello joint might not, especially with relatively fresh wood.

[Davide Sora]

3 hours ago, Jay Higgs said:

Thanks Jeffrey!  I just ordered the 192.  --Jay

I suppose 192 can also be used successfully, but from this test, it looks like you'll have to use it at a pretty low dilution.

For the test, the Milligan & Higgins 192 gram strength glue is exactly what they used:

https://fixitwithshading.com/2015/08/02/the-ultimate-glue-test/

 

[fiddlecollector]

2 hours ago, David Burgess said:

One can temporarily produce almost any climate desired for gluing operations, without much expense or trouble.

Yes i suppose, ive since used a split aircon on heating mode when i need to use hide glue.

[Jay Higgs]

Thanks Davide!  You must be using something like Nikawa WN-001S, jelly strength 340 +/_ 20.  Until now, I thought that was not good for joints, as it wouldn't penetrate the wood well enough.  I have their 2SB, which has jelly strength 250; but I have never used it.  I probably diluted my 3B too much for the cello, concerned that I would not get a good grip when rubbing.  

[Don Noon]

Glue sizing the joint surface probably helps, but there is still an expansion problem with putting hot, wet glue on figured maple. 

The expansion longitudinally is the primary problem which bends the wedges and makes the gluing surface convex, with increased gap at the ends.  It is more of an issue with figured maple, where the grain is not 100% along the joint, but some tangential grain is involved, which increases the expansion/contraction longitudinally.  Spruce is almost always straight grain along the joint, and I haven't seen end gapping issues with it.

 That's a potential glue joint uniformity issue; then there's the later environmental heat/humidity variations tending to pull the ends apart.  If the humidity changes slowly enough, everything should move uniformly.  If the humidity drops more rapidly, the endgrain would dry out and cause gapping at the ends, but also if the wedges are left uncarved, the outside edges will dry/shrink faster, also tending to cause end gaps.

There are a few ways to combat all of this.

• Make the sufaces slightly concave, so that the small amount of expansion/bowing during gluing will make the joint more flat.
• Paint some hot water on the outer edges of the plate (opposite the glue joint) to counteract the bowing
• Cut out notches where the C-bouts will be to lower the stiffness of the wedges, and clamp  at the ends (and the middle too)... see photo.
• You might want to rough the outline and graduations as soon as possible to lower the forces tending to separate the joint during weather changes.

Then there's the gluing issues.  Stronger glue sounds good.  Gluing in a hot room to assure the glue remains liquid, yeah, that too.  

[John Harte]

6 hours ago, Jay Higgs said:

Thank you for your perspective, fiddlecollector.  I plane the surface minimally concave, then after glue sizing I give it a fine shaving once more before gluing.  Davide Sora says he makes it concave just enough to see a trace of light through the center, and if I recall correctly, he doesn't glue-size.  I will probably try that.  My understanding is that Bloom strength does not equal joint strength.  It is a measure of the surface stiffness of the gelatinous stage.  Higher bloom strength comes from longer collagen fibrils, which penetrate the wood less.  I am using Amasonan 3-B, bloom strength 140 as you point out.  They make 001S and 002SB which have bloom strengths of 340 and 250, which I understand they recommend only for surface hardening such as in the guilding process.  Having said that, in the many old posts I have read, I see some of the pros using bloom strengths in those high ranges.  I have some 2-B (Bloom 250) that I have not used; I may do some experiments with that.   Your bloom strength of 190 seems like a good range; where do you purchase it? 

Jay, I have had some recent experience with Amanosan 3B glue including using it for centre joints.  It seems capable of producing a good strong glue joint but, amongst a raft of things, water to glue ratios used are important.

I am a bit short of time at the moment but will hopefully be able to mention more in a couple of days time. 

[Jay Higgs]

1 hour ago, Don Noon said:

There are a few ways to combat all of this.

Thanks, Don.  I was overconfident after my successes with violin backs, and 1) jointed the huge wedges without any cut-outs,  2) as above probably used too dilute of glue for Bloom 140, and 3) confidently ignored the back while I worked the top and sides, leaving it to bend and separate over the last 6 months.  I will use many of your suggestions.  

 

1 hour ago, John Harte said:

Jay, I have had some recent experience with Amanosan 3B glue including

Thanks, John.  I look forward to your experience.  As mentioned above, my violin backs seem solid with the 3B, but for the cello back, I will probably opt for their 2SB after experimenting with it.  

[arglebargle]

This has nothing to do with your glue choices.

Your joint is not good enough.

[Jeffrey Holmes]

18 hours ago, Davide Sora said:

I agree with fiddlecollector, I am one of those who use glue with bloom strength 315/350. The high bloom strength should also indicate that the protein chains are longer than with lower grades, so I prefer to use that for important structural gluing. I am using Nikawa (Amanosan), and recently I got some Bjorn 315 High clarity that I will try when I run out of Nikawa (I have little left).

I think we all tend to adopt systems and materials that work have proven to work well for us personally and glue is certainly one of those things.    It's great to hear other's approaches and preferences.

As for me, I believe that between conservation work, making and restoring I've tried most animal glues (rabbit, hide, bone, etc.) glues at various strengths with the exception of deer hide (which a colleague calls "Bambi Glue") which was popular with a number of European restorers a number of years ago. 

I use 315 for repair joints when I want a very strong semi permanent bond, application doesn't require much manipulation (like sending it through a tight crack without the glue being overly diluted) and I can quickly assemble/clamp. Working time when dissolved in a ratio to actually provide 315 g strength is quite short.  Over dilution makes it weaker than the rating. I also don't use it for patches, as I've seen some evidence that it may cause some distortion (faint outlines of several  patches glued with 315 were visible on a Guadagnini that I saw about 9 months after the restorer completed it).  Now I fully understand there may have been other factors at play, but I'd never seen it to the extent I did on that fiddle... I do know that 315 has the capacity to chip glass as it shrinks and dries and I believe some glass artists use it and higher strength hide glue for that purpose).

I also have 251 and 192 which work nicely for me (and are my go to glues). The 192 working time is slightly more convenient for a number of tasks and (maybe surprisingly) I find it more successful when gluing on replacement fingerboards.  I find the 3-B has some qualities the other 2 two I just mentioned don't, and I've not seen downsides in projects I've employed it thus far (as I mentioned, it's bond strength tests rather well...(I think it hits above its weight class"). I've not tried the higher bloom strength Nikawa glues.

I believe @David Burgess and @Mark Norfleet mentioned they have glue in the 200s (cant't recall if it was 220s or 250s) that they adjust by dilution for the task at hand.  I believe it was from Bjorn if memory serves.

Carry on!  I'm following!

[Michael Darnton]

I think the problem of dry joints is underestimated. If you're using a rubbed joint with a slight hollowing, holding down too hard (especially at the ends) while you rub it's easy with some too much enthusiasm to rub all of the glue right out at the ends leaving nothing to do the job. Likewise for clamping too early while the glue is still fluid, and using too much clamping pressure. Also, I don't like clamps because they can distort the plates somewhat opening up places you didn't expect to open. 

For myself, I use a rubbed joint with minimal rubbing. If you want to take it a step farther, and sometimes I do, you can do like the 1700s and score the joint diagonally with your toothed blade to make it harder to press or rub out ALL of the glue. This works surprisingly well for me.

[CJones]

17 minutes ago, Michael Darnton said:

while you rub it's easy with some too much enthusiasm to rub all of the glue right out at the ends leaving nothing to do the job.

As an absolute beginner this is absolutely easy to do. I had a post a while back where this happened and when asked Davide said my joint was starved. At the time I questioned this silently because I had rubbed and rubbed it never really grabbed like I thought it should   I quickly slathered more on in a newbie sweaty panic and rubbed it all out again. I later theorized that my diy hot box.( a heating pad in a dresser drawer covered with clothes left for over an hour) probably kept things fluid too long (probably the wood was too hot) thus excessive rubbing starved it. I even pre sized it. As soon as I started carving it snapped. I later realized that Davide was right. Imagine that!  I was glad I didn’t argue. 

[Davide Sora]

23 minutes ago, Jeffrey Holmes said:

I think we all tend to adopt systems and materials that work have proven to work well for us personally and glue is certainly one of those things.    It's great to hear other's approaches and preferences.

As for me, I believe that between conservation work, making and restoring I've tried most animal glues (rabbit, hide, bone, etc.) glues at various strengths with the exception of deer hide (which a colleague calls "Bambi Glue") which was popular with a number of European restorers a number of years ago. 

I use 315 for repair joints when I want a very strong semi permanent bond, application doesn't require much manipulation (like sending it through a tight crack without the glue being overly diluted) and I can quickly assemble/clamp. Working time when dissolved in a ratio to actually provide 315 g strength is quite short.  Over dilution makes it weaker than the rating. I also don't use it for patches, as I've seen some evidence that it may cause some distortion (faint outlines of several  patches glued with 315 were visible on a Guadagnini that I saw about 9 months after the restorer completed it).  Now I fully understand there may have been other factors at play, but I'd never seen it to the extent I did on that fiddle... I do know that 315 has the capacity to chip glass as it shrinks and dries and I believe some class artists use it and higher strength hide glue for that purpose).

I also have 251 and 192 which work nicely for me (and are my go to glues). The 192 working time is slightly more convenient for a number of tasks and (maybe surprisingly) I find it more successful when gluing on replacement fingerboards  I find the 3-B has some qualities the other 2 two I just mentioned don't, and I've not seen downsides in projects I've employed it thus far (as I mentioned, it's bond strength tests rather well... I think it hits above its weight class"). I've not tried the higher bloom strength Nikawa glues.

I believe @David Burgess and @Mark Norfleet mentioned they have glue in the 200s (cant't recall if it was 220s or 250s) that they adjust by dilution for the task at hand.  I believe it was from Bjorn if memory serves.

Carry on!  I'm following!

Great overview on the use of glue, which shows its versatility if used with awareness of its characteristics, which remains the key to successful gluing. Unfortunately, here in Italy, it is not easy to find a seller who provides the technical data of the glues, but we are improving. Together with the Bjorn 315 that I received and that I still have to try, and that I would like to reserve for important structural gluing, they also sent me the 192, which I plan to use for all other gluing. I will see how it works. I also have the Nikawa 140, but I confess I have never tried it, and another Japanese glue with unspecified characteristics that they brought me a few years ago and that works fine. I am overwhelmed by glue, I do not think I will be able to finish it in this lifetime.

[nathan slobodkin]

15 hours ago, arglebargle said:

This has nothing to do with your glue choices.

Your joint is not good enough.

I am afraid I have to agree with this. I have glued quite a few cello backs and have given details of my methods in previous MN threads. Unless you are using some really odd glues problems with center joints are almost always caused by the shape of the joint. A dry joint with a catenary relief of a 1/2 mm or slightly less which closes perfectly with a single clamp in the middle closed finger tight will not fail. The key is to look carefully at the joint as it closes with a strong light behind it. If the light through the joint disappears evenly from both ends as you tighten the clamp until it is completely gone then tighten the clamp enough that you can look carefully at both sides. If there is any where along the joint on either side which does not look perfect the do it again until it is right. Both bumps and twists anywhere will cause the joint to fail.

[jacobsaunders]

22 hours ago, fiddlecollector said:

alot bigger and probably more movement with climate changes.

blame it on climate change, that's a good idea

[David Burgess]

1 hour ago, jacobsaunders said:

blame it on climate change, that's a good idea

Maybe so. Claiming a loss due to a "natural disaster" might make one eligible for all kinds of government assistance. 

[Jay Higgs]

 

On 5/17/2025 at 2:12 PM, David Burgess said:

Claiming a loss due to a "natural disaster" might make one eligible for all kinds of government assistance. 

I used AI to check your suggestion David.  I actually got a serious response.  The bot stated that my cello back split would have to have occurred during a federally declared natural disaster, and the issue would have to affect my professional income.  San Antonio winters are not a disaster and I am not a professional, so I cannot claim the loss of 1 gram of hide glue. 

However, this thread has been very enlightening, and I am glad I shared my failure.  I haven't yet done the cello back again, but I did a violin back yesterday.  I used Amasonan 2B (Bloom 250) with a little more than 1:2 dilution, a rub joint and gentle clamping, trying to emulate Davide Sora's slight concavity.  I planned on abandoning the 1:2 dilution if I couldn't get a good grip on the rub, but it gripped well.  Attached are the 24 hr later views of the joint and a couple of chip break tests.  The exterior end chip broke partially on the joint line and the interior chip did not break on the line.  I will paint the ends for storage.