Top shear into soundhole - glue recommendation

[mhackney]

My 19 year old Lakewood D-14 has had a tough life for the last 10 years. It spent several years in Virginia with my daughter working at a year-round outdoor camp for boys where it spent time in hot cars and finally moved to Colorado with her 2 years ago.

I've done a number of resets and crack repairs and have built a few guitars and other stringed instruments so I'm competent to use tools and materials and want to resurrect the beautiful sounding instrument!

The guitar has the dreaded "top shear into the soundhole" accompanied by the tell-tale cracks alongside the fretboard extension. You can see the damage here:



The dislocation is small, maybe .5mm, and the neck position is still quite playable. But this needs to be fixed. And, of course, there is other damage to contend with but I have experience with the separating bridge repair (due to heat) and top seam separation from bridge to end block repair.

Lakewood uses a bolt-on neck with a glued-down fretboard extension. Removal of the neck was straightforward, leaving this:



I contacted Lakewood about the issue and Martin (owner) was very helpful with information. They've built 30,000 guitars with this neck attachment and had no systemic issues AND I know that this instrument was left in a hot car, in the sun for extended periods. Even the Hiscox case is faded in areas

As you can see, there isn't a lot of surface area for the fretboard to glue to. That large opening is to accommodate the truss rod as seen here:


(note a strip of the top came off with the ebony fretboard - an easy fix)

Here is the crushed purfling accompanying the sheared top:



Using heated spatulas I carefully separated the top from the cross brace, the flat reinforcements about mid way of the opening and the neck block. The top is completely free. It still was not possible to push the sheared top section into place - that required gentle heat and a jack-rod as shown here:



The sound hole is now perfectly aligned and the crushed purfling now in the proper position.

There isn't a lot of surface area to attach additional reinforcement under the top but I will add as much cross-grained splints as possible along with a soundhole reinforcement.

My question relates to glue. Given the small surface area for gluing and the goal to mitigate shear forces to eliminate future damage (and, of course, this instrument will be treated with TLC now) what is a better glue to use - Titebond, Titebond III or fishglue applied cold? Or is there a better option?

Thanks in advance!

[John Arnold]

If you can do it, use hot hide glue. I don't do cross grain when cleating these. I use 5/32" thick quartered spruce that is tightly fitted between the neck block and the transverse brace. That prevents the shift from occurring again. Angle the outer edge so there is no stress riser. In general, the patch is the same width as the neck block at the upper end, and widens to the width of the soundhole where it contacts the transverse brace. I use the same reinforcement when building a new guitar. No cross grain popsicle, ever.
Consider the cross- grain joint that failed (the upper transverse brace) in order for the shift to occur.

[mhackney]

Thanks John. I can use hot hide glue (a little more work but doable).

Here is a drawing (not to perfect scale) of things.



Are you suggesting that I remove the flat braces (they are truncated at the neck slot) and then patch something like I've shown in blue?

[mhackney]

Ah, for my blue patch it should widen to the diameter of the sound hole - I went a little too far with my quick drawing!

[mhackney]

Like this



Where the large blue patch is quarter sawn sitka (my top material) with the grain aligned with the top grain.

[John Arnold]

That is it. You don't have to remove the flat brace (aka popsicle) if you would rather not. You can fill in the areas above and below it with spruce that is the same thickness, then overlay it with a 1/8" thick patch. Alternately, make a thicker patch and cut it out to fit over the popsicle. The main thing is to fit it tightly between the neck block and the transverse brace.
The patch you show between the transverse brace and the soundhole is not critical. I generally just put one there if necessary to make the top flush on either side of the cracks.

[mhackney]

Thanks again John. I get it, the patch distributes the load from the neck block up to the transverse brace!

I removed the flat braces today - they were so weakly attached that they popped off easily. This will make for a cleaner repair with the new patches.

Now I am considering removing and regluing the transverse brace. I am concerned that with all of the heat (from being in a hot car for extended periods) that the brace is not well glued.

I can eliminate the patch between the transverse brace and soundhole then, as everything is flush.

cheers,
Michael

[Rudy4]

Seems like you're well on the way to getting things structurally reinforced.

The couple of guitars that I've seen this happen to are case studies of the value of the popsicle brace that extends un-compromised across the underside of the top. Without that brace the force of string tension often over time will cause a rift along the top plate grain, as seen here.

My repairs were done by pulling the neck back in position, which re-aligned all the other shifted areas, and adding a substantial brace between the side of the neck block and the underside of the top plate. These were about half the height of the top block and cut at a 45 degree angle. A small notch was added at the top for binding and the block glued in with Titebond Original.

I added a popsicle brace as further insurance against a repeat performance.

In my case, it was better to not remove the neck and that saved a boatload of labor. I'd hazard to guess this guitar has an extension under the fret board that necessitates the lack of a popsicle brace. I wouldn't feel bad about whatever modification it takes to remove that "feature".

This malfunction often effects the integrity of the transverse bracing, so that's something to check on, too.

[mhackney]

Thanks Rudy4. Yes, you can see in the photos I posted that there is an extension under the fretboard for the tension rod. That necessitated that the soundboard has a large slot in it from the neck block to the near the soundhole.

This guitar saw extreme worse case "never do that' heat. It is a miracle it didn't all just fall apart. Maybe hidden damage will turn up after these repairs but I have spent a lot of time looking at and testing all of the braces and scrutinizing the guitar with magnification looking for issues.

When I learned of the damage in September when we visited my daughter in CO I took it to a local luthier. He wasn't sure that the neck was a bolt-on so had to assume a dovetail removal (there was a large piece of velcro on the neck block that had pealed off leaving the black adhesive residue. The bolts are then underneath a press-fit piece of mahogany to disguise the bolts). With all of the heat and dehydration damage, he didn't think the guitar was worth the repair investment (it's a ~$2000 guitar!). I brought it home to MA and rehydrated it for months carefully back up to 45% REL. All of the protruding frets are now flush again (almost miraculously) and the dips and wrinkles in the top between braces have literally all rebounded. I didn't expect this much recovery with rehydration. I planned to use this guitar as a learning experience but I think it will make a full recovery and be playable once again.

I have everything ready to reassemble now. Mixed up some hide glue and once it is hot, I'll start to glue things together. I pulled the bridge off last night - it certainly showed evidence of heat fatigue. I know that Lakewood uses Tightbond and there were threads of glue from the top to the lifted back edge of the bridge indicative of softening/melting of the adhesive.

[John Arnold]

The only way this shift can occur is if all three of these joints fail:
1) The upper transverse brace inside the cracks.
2) The popsicle brace inside the cracks.
3) The neck block ouside the cracks.
All three of these joints have one thing in common; they are all cross-grain. Cross-grain joints are notorious for loosening, especailly when subjected to heat and/or low humidity.
That is why I use and recommend the trapezoid patch. It is much less likely to come loose, and the tight fit prevents the neck block shift from ever occurring. IMHO, a popsicle is a poor substitute, for the reasons I just outlined. Even if it were tightly fitted, it would not remain tight over time, due to natural cross-grain shrinkage.
An added benefit is less damping of the top in the upper bout.

[mhackney]

As a scientist and engineer, I understand and appreciate your analysis and proposed fix John.

I made a template for the trapezoid patches from card stock to test fit. They fit perfectly. I've cut them from quarter-sawn spruce and tested the fit - nice press fit on both sides. I did extend a little wider than the soundhole.



I patched the damaged/missing section over the seam near the rosette. I also glued the cracks shut and reglued the purfling at the neck block.

Here's how the template looks in place (I put a piece of spruce over the slot in the soundboard to eliminate the backlight). The pencil mark is the actual diameter of the soundhole. Note that there is no trace of the old popsicle stick brace that extended from the slot to the right - that glue completely gave way.

https://mhackney.zenfolio.com/img/s/...25808546-4.jpg

Here I've reglued the top to the neck block and the transverse brace. I paired the center seam patch flush to the top. I used original Tightbond on these, I'll use HHG on the trapezoid patches. I decided against removing and regluing the transverse brace. Its ends were secure and it was easy to work in Tightbond using a syringe and dull needle and thin palette knives. I had good glue squeeze out when clamped. Cleaned all the squeeze-out up with moist Q-tips.

Once this is all set up, I'm ready to install the trapezoid patches.

[mhackney]

I've completed the top shear repair and tested the neck angle and it is back to normal unstrung. The guitar had a number of other issues that I Alsop repaired:

• the lifting bridge was removed, cleaned-up and re-glued
• re-reamed the peg holes and fitted new ebony pegs (2 on it were poor replacements)
• made a new bone saddle from a blank, it turned out great
• repaired a top crack with reinforcement cleats and carefully touched up with varnish
• installed a new end pin to replace the removed pickup system's jack
• filed and crowned the first 4 frets and polished all frets

This morning I re-glued the fretboard extension and installed the neck bolts and tightened them up. It's all clamped until tomorrow when I'll string it up to test. Exciting!