remedy for open center seam while building

[John R]

Hi Everyone,

I have a building question about what to do, or do nothing?, about opened top seam while building. This is my first post so a preamble introduction I suppose my help also.

I have recently joined after many years of reading and learning here. I am a woodworker by trade and returned to hobby guitar making about 15 years ago and have done elec's and acoustics. By reading on inet and books I have been able to get to some competence but now have questions come up that could benefit from pro advice.

Last year I began a round of builds to push my skills as best I can. I now have necks blocked out and 4 boxes closed and other sides bent etc, using up woods I have collected. Now getting back to these this fall/winter.

I use wood heat to control my build climate and am fastidious about staying in 40-50% @70* +. But some times things must sit and thus some variation occurs in storage. Last year a top seam opened in one of these closed boxes during sierra summer where I live. It is tiny but runs tail to rosette it appears and closes at 50%, when RH drops it is visible but not 'open' per se, maybe .002"? Searching for answers didn't yield much info.

This one is EIR and adirondack slope dread braced per hd28 typical. Round shoulder because it's easier for my bending method and form type. Also of about 1 dozen acoustic builds this is the first opening during building which I assume is lack of full multi season drying cycles. My others have been sawn from sitka 6/4 and redwood I have had for a few decades now and no problems.

The Adi I bought from Old Standard as my first time using this spruce - it is aa grade 3 pc stock to keep cost down as I learn. I suspect I needed to store it for 2 seasons minimum, but instead I had it only 6 months as I recall and went to building. Seam is glued HHG which I am getting toward using for everything as my ambition is to build in older methods and more folk instrument appraoches to keep simpler and healthier as best possible from *dusts* etc.

So I am interested to hear what others do when this happens. It seems my best 'option' may be no option and let the top lacquer 'fill' the seam and accept it as-is. My finish plan is Laq top with all else rubbed out burnished oil.

Thanks for any advice and suggestions.

John R

[charles Tauber]

I'm puzzled by the seam opening during the summer. In many climates, it is more humid in the summer. Since wood shrinks as it looses moisture, it seems unlikely that low humidity/shrinkage would be the cause of the seam opening. Is it dryer where you live in the summer than the winter?

You mention using hot hide glue. I have had LIQUID hide glue joints fail in higher humidity and temperature. Could it be related to your hot hide glue technique? (You mention the others are fine and the this is the first.)

As I'm sure you are aware, there is a difference between "drying" and "seasoning" wood. If you bought the top wood fully dry, and maintained the humidity level more or less at a constant, it isn't likely that dryness is the cause. If the wood is dry, it isn't necessary to "cycle" it through seasonal changes. If the wood is properly dried, acclimating to your building environment should only take a week or two.

It sounds like the humidity dropped between when the guitar was assembled and when the seam opens. That is, the guitar was assembled at too high a humidity level.

Photographs would help those here to see the magnitude of the issue. It seems that you have the usual options: do nothing, fill the open seam with a mixture of wood dust and glue or insert a thin splint of matching wood. If the humidity was too high when you assembled the guitar, you'll likely have recurring issues with the seam whenever the humidity drops below the 50% at which you notice the problem. Whatever work you do should be done at a "low" humidity when the problem is towards its worst.

[Howard Klepper]

"The sierras" covers a lot of ground. Much the Sierra Nevada range has low humidity in the summer. Please be more specific. And photos of the top help.

Are you sure the glue failed? Often tops crack immediately adjacent to the glue line and it is hard to tell.

Are you saying the crack or seam separation now closes in low humidity and opens above 50%? I can make no sense of that.

[tadol]

Non-luthier here - keep that in mind -

2 thousandths? On a 3 piece top? i’d think you could rub a little glue in there and clamp it up, and throw a couple small cleats under it. And if it doesn’t look as good as you’d want, might be a great chance to try shooting your first sunburst!

[John R]

Thank you all for replying. I have a few pics of these tops & as best I can get, and these are still in the rough and pics not too clear.

I was a bit embarresed after posting due to having read many times about this ? and sensing there is no real set easy answer, but was curious about how experienced luthiers and repair tech's may approach it.

My assumption is just finish it and let it be. If it rattles etc (unlikely) then I can learn-by-doing a rout and fill with same adi I have. Still have the second set of this in what as I recall he lists as 3 pc top. Idea being 2 main pieces with wings at lower bouts. Because I am learning still I stretched this first set into 2 guitars- this dread and another shortened dread 14.5 fret to body at 19.75" long, again learning experiment and using up wood not too expensive - ie padauk in this case.

Hi Charles - I think your correct that I assembled at a higher humidity then it dried out further. And it definitly cycles open at 45%- then it will close to eyesight anyway at 50%+. Not a big deal really.

Hi Howard - Sierras by way of nevada city. Very dry here in summers but my room (just moved into a nicer room)then is all raw pine interior that I think buffers swings very well as opposed to painted walls. Once warm and stable it holds well over night. But also I am building in a simpler methodology now just to save and limit my usage of 'stuff' and that may bring some of these errors in play, and then need to find solutions.

Hi Tadol - I think .002" is too large ,it is tiny, and as Howard said too it may be a fracture not glue fail. Yes the chance to learn so reapir and interior cleating through the soundhole may be next. And paint is good if/whn like the clapton black OM's a few years back with likely colored adi that then few could stomach-look where it all is now with any good sounding materials in play. No sunburst experience yet but my first real acoustic in 1982 was guild d25M in the dark mahogany I would love to do one now.

My HHG experience is about 8 years now but only a few times a year, but have had no other problems, many neck builds, FB's, tops and bracing in go bar deck etc. Reading before I tried I got that having parts to warm ambient and ready to go, and room hot gets reasonable working time and that was easy to do in my case with small room and small wood heat. I go to 85-90* when I have hhg glue ups.

I'll put up these pics - first 2 are this eir hd28-ish and others show as usual no seam problems - 3rd pic is short dread with adi, 4th is a 12 fret smeck/jackson browne type thing, and then a slope jumbo-ish maple/sitka to guild d25 bracing. Last pic is a compound bent archtop sitka jazz box I did about 10 years ago that has had zero issues....Thanks again everyone, John R.

[Howard Klepper]

John, no need for any embarrassment. Your workmanship looks good. We all have much, much more embarrassing stories than a center seam opening from low humidity. That's not into embarrassment territory at all.

It's clear to me now that it is closing above 50%, not opening, which didn't make sense. What you should do now is get humidity up above what it takes to close the crack or seam (doesn't really matter which it is if you use hot hide glue to fix it). Get it well above 50%--like in the 70s, because it will continue to close tighter. That will probably require a room humidifier, since warming the room drops the relative humidity. IF the seam is closed and the two sides align well, you can glue (if the edges don't align, come back here for more). Work in hot hide glue (a little thinner than you would use when first gluing) by flexing the edges of the crack/seam up and down just a little bit with glue on the seam, and rubbing the glue in. Wipe off excess glue both inside and out with a damp warm rag before it sets up. Apply very gentle pressure across the top with a couple of clamps if that makes it look any tighter, but that may not be needed--you don't want to clamp much and have the seam peak up, or to stress the top too much--just to try for as invisible a fix as possible.

When it is dry a day later, put a line of small spruce diamond shaped cleats every couple of inches along it inside (look for photos on the web or at Frank Ford's frets.com site--I'm sure he has something on how to do cleats). You can do a rub joint on these without clamping. You will probably need to sand a little with a block to clean away any remaining glue and get the seam flat.

It is much better to fix this now than to just go ahead as if it isn't there. Much, much better. No-brainer much better.

For the future, you don't need to glue the center seam with hide glue, even if you think it has advantages for other joints. The center seam is one that never needs to be opened, and I never heard anyone claim that it matters for tone what glue you use for it. I know a prominent builder who is known for using hide glue on his guitars who glues the center seam with Titebond, because it is more reliable and there is no need to rush to get it clamped before it gels.

What you are doing with the wings is called a four-piece top, not a three piece. John Griffin's wood for those tops is a bargain. You can be sure it was appropriately dried before you got it. He is a good, reliable supplier.

[redir]

FWIW I know a lot of luthiers do rub joints with HHG on tops and maybe even backs but the only time I had a center seam fail was when I did that method. I always clamp the joint now. In fact when I clamp it I also use heat so the HHG doesn't even come close to jelling up and the two halves come together tightly.

Done right the center seam should be totally invisible. If you see what looks like a grain line at the glue joint then it's too thick and will probably come apart under some stress.