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In my effort to make every possible mistake as I learn how to build, I have managed to make my fourth guitar have a concave top. My other 3 guitars had nice convex tops.

I live in a somewhat dry area of southern California. I store my wood in a cool dry place until I am ready to build. When I know what I am going to build, I put the wood in a large sealed plastic shipping container, with a damp sponge in a a plastic box with holes in it and a digital hygrometer with the humidity at about 50%. I like to leave the wood in there for 3 -4 weeks before I start using it. I do not measure the moisture in the wood.
I built this guitar with 15' radiused braces and glued them on the top with a radius dish on a go-bar deck just like my other guitars. I have kept it in a case with the humidity controlled at about 50%.
I have had a lot of trouble finishing this guitar and it has been out of the case a lot. I noticed the concave top a while back, but I thought it would correct itself when I put it in a case with higher (50%) humidity. I just completed the satin finish and after about a week in the case, it has not moved, or has gotten worse.
I have no idea what I should do with it now.
I figure that I must have built it much more wet than I thought, and it shank to this shape.
Do I keep storing it at high humidity and hope? Can it be corrected somehow?
Do I just forget it and realize that this is how it will end up?
Should I start measuring moisture in the wood before and during building?
Thank you for you input.


I'm sorry about the poor quality of the pictures.

That is a 1/16" drill in the pictures. The third pictures show that the top is flat in that difection.

_________________
"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

Steve,
I am guessing that the top will belly "up" once it has string tension -
giving you a concave lower bout. As long as your neck angle allows you
to have some adjustability with the action and the guitar is structurally
sound from the bridge to the headstock - I think it will be fine. I wouldn't
be too worried.

I will be interested to hear what the other OLFers say.

Beautiful guitar,
Simon

The only time i've seen this before was when the gluing was done in higher than optimum humidity conditions. The collapse happened when the humidity went down.
A young fellow who works with me had his top collapse & it only got worse when strung up. After a year, he is now replacing the top.
I sure hope your beautiful top bounces back! Love the spalted rosette.

Steve,

I make my instruments with the top braces radiused to 13' and the only time I have had this experience was in the very early days when I didn't have proper humidity control and braced the tops in high humidity and watched them go concave as the humidity dropped down. This was before the tops went on the body and I had to correct by rebracing.

A few questions though. Was the top nicely domed when you first closed the box and how did you profile the sides? Most of the "doming" in my tops occurs from the back of the soundhole to the tailblock area, and the shape the sides need to be to accommodate this is to say the least complex. In particular the edges of the lower bout drop down considerably and the tailblock is a lot lower than the neckblock to accomodate the shape. If you don't get this right you can undo the doming by having the sides too high in these places and gluing the top down. I only say this as in your pictures you appear to have the high points at the lower bout edges and tailblock. It could be the humidity but could also be the side profile not being correct. Have you got any pictures of the side profile at the lower bout/tailblock area? Here's what mine look like in this area:



Either way imho I don't think the dome will come back - if it's a himidity issue you'll have to re-humidify and keep it there but when the humidity drops it will sink again. If it's the side profile then you will have to carefully remove the top, reprofile to the correct shape and put the top back on again, re-bind and re-finish. In this scenario when the top comes off you will see if it goes back to the original doming.

Hope this helps.Dave White38940.1609490741

_________________
Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

Humidity is the invisible aid in building. I like to glue up tops and backs when it is drier. 45% or so. If you glue up in higher humidity the top will sink in drier conditions.
Not much you can do but live with it or pull the braces and reglue. I have a few early sinkers myself that still play well.
john

[QUOTE=Dave White] A few questions though. Was the top nicely domed when you first closed the box and how did you profile the sides? [/QUOTE] Dave,
Thank you for your help.
The top was nicely domed. The sides are sanded flat and then the upper bout is sanded to provide the 1.5 degree.





[QUOTE] It could be the humidity but could also be the side profile not being correct. Have you got any pictures of the side profile at the lower bout/tailblock area? [/QUOTE] Hmmm,
you have me thinking. I sand the sides perfectly flat. 3 guitars are great, one is bad. My guess is humidity.

When I built this guitar I believe I kept the top well humidified, but the braces might have been dry. Could that explain my trouble?

_________________
"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

[QUOTE=SteveS]   you have me thinking. I sand the sides perfectly flat. 3 guitars are great, one is bad. My guess is humidity.

When I built this guitar I believe I kept the top well humidified, but the braces might have been dry. Could that explain my trouble?
[/QUOTE]

Steve,

Did you make the other 3 guitars with 15' radiused tops? In my view/experience a 15' domed top clamped to flat sides will give you the result you have - the dome "high point" around the bridge/lower bout wants to stand tall and so the sides here are lowest compared to the rest of the top edge (see the picture I posted). Keeping the sides straight and then clamping the top will flatten this dome to get it to fit. Same thing with the fall off from the soundhole to tailblock if you don't lower the tailblock.

I actually did this to a top once using Cumpianos method of gluing the top by clamping to the workboard - that's when I gave it up and spent lots of time getting the side profiles absolutely right so that the back and top can be glued in place just using brown tape to the sides with neck and tailblock installed.

I don't think the dry braces are an issue.

_________________
Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

It has been quite a while since I lived in Southern California but if I recall, you don't have wide swings in Humidity normally. I wouldn't try to adjust the humidity unless you are wildly swinging and plan to ship guitars to other areas of the world. If you are building for your own local, I would build them to your own stable humidity level and not worry to much about being at a proper humidity level unless it is a high humidity and I certainly wouldn't add moisture. I know a couple builders who like building at what I consider very dry levels (25 - 30%) since a shrinking guitar is the one that will suffer damage while a swelling guitar usually only suffers from poor action and tone. I prefer to build at around 40% which is a pretty easy figure to reach in my part of California.

_________________
Tickle your guitar daily, and it'll tickle you back.

Steve,
the problem is that you added moisture to the wood, braced it, then
glued it to the rim. At this point the wood gave up its moisture content to
the low humidity environment you live in. The top shrank across grain.
Because the braces don't shrink lengthwise, but the top shrank across the
grain, the top curved in the opposite direction. You would actually be
better off leaving your wood exposed to the low relative humidity of your
home before building with it. Once built, the guitar can absorb quite a bit
of moisture without damage. Most of us have the reverse issue to deal
with -- that is, building an instrument in higher humidity and then
sending an instrument to a drier place, which results in major issues like
cracks, splits, and seams opening. Your building environment is much
more forgiving.
Craig S.

[QUOTE=Dave White] Steve,

Did you make the other 3 guitars with 15' radiused tops?
[/QUOTE]
Dave, Yes - all of my guitars have been built the same way. Three of them are great. I'm thinking the only variable is humidity. 2 cedar tops, 2 sitka tops, all sitka bracing.

_________________
"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

[QUOTE=John How] It has been quite a while since I lived in Southern California but if I recall, you don't have wide swings in Humidity normally......[/QUOTE] John, Thank you for your help. We don't swing too much, normally, but this has been a strange year. We can go from the teens to almost 60% on any day. The 60% is mostly at night when the moisture from the ocean comes in and cools us down from the hot day.

So what you are saying is that I not be that concerned unless I am shipping it to a humid environment or It happens to be very humid here. Great- my next one is going to New York. Should I try to build at about 40%?

How long does it take wood to react to moisture? Is it a matter of days or hours?

_________________
"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

Build to the environment where the guitar will go but err on the dry side. You should try to stay on the 40-50% average but dry. Does that make sense?

_________________
Tickle your guitar daily, and it'll tickle you back.

[QUOTE=csullivan] Steve,
the problem is that you added moisture to the wood, braced it, then glued it to the rim. At this point the wood gave up its moisture content to the low humidity environment you live in. The top shrank across grain.
Because the braces don't shrink lengthwise, but the top shrank across the grain, the top curved in the opposite direction......[/QUOTE]
Craig,
That makes sense.

[QUOTE] You would actually be better off leaving your wood exposed to the low relative humidity of your home before building with it. Once built, the guitar can absorb quite a bit of moisture without damage. Most of us have the reverse issue to deal with -- that is, building an instrument in higher humidity and then sending an instrument to a drier place, which results in major issues like cracks, splits, and seams opening. Your building environment is much more forgiving.
Craig S.[/QUOTE]
It sounds like this is the second recommendation to go ahead and build on the dry side.



I check out my digital hygrometers last night. Can you guess which one I was using to monitor the humidity in the case where I was bring up the moisture level before building? Of course it was the one reading the lowest. I must have put too much moisture in the top.

_________________
"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

Some questions.

1) Should I start checking moisture content in the wood?

2) Will this guitar be stable in a dry environment?
3) Would it be better off in a humid environment?

I have started my next 2 guitars and right now I don't know if I want to rebuild. I guess I'll have to think about it. I know a local kid that could use a new guitar. If this one will be stable as is, and not sound bad because of this issue, perhaps I'll make him an unbelievable deal.SteveS38940.5884259259

_________________
"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

Steve,
Here is another thought as to the cause. I noticed on one of my builds
that after I attached the top to the rims that when I removed my mold the
top lost some of its curvature. When I put the sides back in the mold, the
curvature came back. What was happening was that these sides had a bit
of springback and wanted to be a bit bigger than my body shape. The
unattached part of the rim (mainly at the tailblock) tipped outwards
causing the angle of the sides to change. In other words, instead of
perfectly perpendicular sides they had a slight angle which in turn
affected the curvature of the soundboard. I made sure that the sides
were perpendicular while I attached the back (rope method) and the
soundboard arch came out perfect.

Just a thought but there is a possibility that this occured with this
particular build for you. I still stand by my thinking that if your guitar is
properely humidified and it has been that way for a while and you don't
notice any structural issues - you won't have any trouble. The string
tension WILL pull the top up some (depending on how lightly braced the
guitar is) - hopefully enough to give it a flat surface or maybe even a
slight arch. SimonF38940.6269328704

Simon,
I strongly suspect the issue is humidity related. I hope your are right about the strings pulling the top up some. I really do not want to rebuild this guitar. If it comes up some and is at least flat and not concave, I'll be happy.

_________________
"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

Steve, as John eluded to, it's always better to be on the dry side. 1) because there are more areas where it's dry than wet and 2) because lack of moisture affects wood much worse than too much moisture.
I keep my shop right at 40% year round and have been pretty lucky with any humidity issues.

Thank you all for your help. I have learned a lot today.

_________________
"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

I read this thread last thing....at 12.30am I was seen to be placing
a staightedge along the lower bout, only to realise that I had the same problem!!!!

I have been quite meticulous with the humidity, although there have been a couple of swings
I missed within an 8 hour period (dehumidifier failing to switch on automatically in the night
...whether it was a power failure or the timer plug failed)

I've been very fortunate this year...we have
had a very dry and temperate climate this summer,
although when low pressure comes in, the humidity
leaps up...


Question is, would my guitar still be playable?

Someone said to set the angle of the neck to accomodate adjusment in action if the top bellies up...
How can this be done?Sam Price38941.1110300926

Steve,

Thanks for asking this question because I just learned alot too.

I wanted to say that I really love the spalted inlay!

While I appreciate the mother of pearl inlays etc and have seen some beauitiful work here; there is just something about the natural beauty of randomly figured wood. Of course it takes some skill to bring the diamond out of the rough but man nothing can top (pun alert) figured wood finely crafted to my eyes.

The side expansion explanation makes the most sense to me for pulling the top out but then in theory the top should stretch and flatten until the sides could angle out no more producing in theory at maximum deflection a tight flat top...kind of like stretching sran wrap over a container. At this point though the flat profile of top of the sides would be at an angle to push the top concave. Okay now by brain is starting to hurt

Here is a question then;

Has anyone used slightly angled kerfing to help ensure an upward convex profile is supported at the rim where the bracing thins out the most?Scooter B38941.4500578704

[QUOTE=Scooter B] Has anyone used slightly angled kerfing to help ensure an upward convex profile is supported at the rim where the bracing thins out the most?[/QUOTE]
Absolutely. In fact, it's pretty much manditory. The full width of the linings should touch the top, so where the top is domed the linings need to follow the same radius. I think most folks here use a radiused dish to sand their lined sides to the proper profile. Some may use a sanding stick, which pivots on a support placed where the apex of the dome will be. There are probably other methods, too, and maybe others will jump in with options.

I decided not to redo the top. I built it and put on strings this morning. If the concave top has a negative impact on tone, volume. overtones, or sustain, I could not tell. It sounded great from the start.

The string tension did not pull the top up.
(The tension is not in the upward direction and there is no pivot/mechanical reason for it to move up.)

A couple of conclusions -
1) If you have a problem with a build, no matter how embarrassing it is, post about it here. You will learn and many others reading will learn.
2) This was a humidity issue. I was over humidifying the top when I bonded the bracing on.
3) It will sound like a guitar when you are done, even if you mess up like I do.

Thank you all again for your help.
Pictures coming soon.

_________________
"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

Here area a few pictures of the almost finished guitar. You have to look close to see the problem.

_________________
"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

Sure looks nice, Steve!

It's a beauty Sreve.

Hey I thought flat top acoustics had flat top and only arch top jazz guitars had an arched top

I'd been hainging out here a month before I ran into go bar decks wich led to sanding dishes and in turn radiused tops and backs.....

Obviously I'm not a Luthier.