Soundboard bulge problem

[Kim de Rijke]

Hi everyone,

I'm afraid most of my posts are of the problem, I-need-your-help type, though I posted with some degree of happiness a few pics of my previous first two classicals. I'm obviously an amateur, but I love the work, the conversations and info on this forum, all of which keeps me sane while working at a University. I'm currently building classicals #3 and 4 for my young kids (one with a WRC top, TBW sides/back and QLD maple neck; the other with an Englemann top, Tiger Myrtle sides/back and QLd maple neck). It takes me a long time to complete a guitar with intermittent building - about 12 months - but they were going well until I went to glue down the fretboards this weekend. Here is my problem:

I follow the Cumpiano & Natelson method, so attached the soundboard to the neck first. The surface on which the fretboard sits was close to dead flat. Now, however, on both guitars the soundboards were bulged in the area from the neckblock to the soundhole. I'm mystified as to what caused this. I guess I'm just seeking input to learn an important lesson because I found myself having to create a kind of ledge of about 1/2mm deep in the soundboard so the fretboard can sit flat. I couldn't seen another solution apart from the opposite, that is, to glue a veneer onto the neck and part of the soundboard to raise the fretboard. Didn't like that either, but in hindsight I should have done that because another problem I just realised this evening is that the clearance at the bridge location is also less than required (1/8" instead of 3/16" to 1/4"). I guess it's another, or perhaps the same bulge going on.

Just thinking about what caused this, I remember the following:

1. the two soundboard braces in between the soundhole and the neckblock were dead straight;
2. the bottom brace is curved as it should be;
3. I glued the bottom brace on just after the summer when humidity was down (but perhaps the variations in Brisbane humidity over the past 5 months or so may have caused this regardless?)
4. I glued down the sides onto the soundboard with a shim underneath the edges of the soundboard. Perhaps the whole box was somehow forced out of whack in that process?
5. Or perhaps it could have happened when gluing the back on with a long strip of car tyre, exerting too much force downward and similarly forcing the box out of whack?

I have no idea, really. The fretboards are on now, but I ain't happy about it. I'm also at a loss about what to do with the bridge. If I just follow the book's measurements I'll have too much action at the 12th. Can I reduce the height of the bridge by, say, 1/16" to 3/32" without risk of bridge failure?

Hoping I haven't bothered you too much with the problems of an amateur, but for my kids I would like these guitars to sound as good as they can look with this lovely timber.

Thanks, Kim.

[kiwigeo]

Are the sides locked into the neck block with wedges? I've had an upper bout on one of my Spanish Method classicals with a deformed upper bout due to the wedges being whacked in a bit too hard. One of the wedges actually punched through the top but luckily ended up covered by the fretboard.

I haven't built using the Spanish method for some time now, preferring to use a bolt on bolt down neck technique ala Trevor Gore. With this method the upper bout is made flat and the slight positive neck rake is achieved by inserting a wedge shaped fillet between the neck and the fingerboard.

[simso]

Do you have photos you could upload.

Steve

[Kim de Rijke]

Thanks Martin,

No, I didn't use wedges to lock in the sides. The sides fitted into the slots snugly, but perhaps a light tap or two I probably applied caused the upper bout to bulge slightly regardless?

Steve, sorry, I have no photos of what it looked like before I laid down the fretboard.

I guess it's now a matter accepting the state of affairs and finding a solution to the bridge/action issue. Do you think I should reduce the bridge height?

Best,
Kim

[simso]

Any photos of where you are would be helpful, use your phone, it will be fine, we just need to see what the top and fretboard kind of look like under tension in regards to your bridge and saddle.

Steve

[kiwigeo]

Do you think I should reduce the bridge height?

Best,
Kim

Reducing bridge thickness may be an option. Do you have a bridge patch installed?

[kiwigeo]

I just realised this evening is that the clearance at the bridge location is also less than required (1/8" instead of 3/16" to 1/4"). I

The 1/8" clearance at bridge location is measured with a straight edge lying along the fretboard without frets installed right?

You can work out where the strings will lay by adding on fret height and an allowance for action on treble string (say 3mm action measured at 12th fret = 6mm at saddle). You can probably also add on another 0.5mm to allow for neck/belly pull up with strings at tension. The final sum of these figures will give you an idea of where the strings will end up relative to top of the bridge and from this you can decide if taking the bridge thinner will help you. On my current Gore classical build the bridge will be around 8mm thick.

[Kim de Rijke]

I'll try to take a photo tomorrow Steve. The bridge is not installed yet, but yes, as you say Martin, I'm talking about the clearance measured with a straight edge along the fretboard. I have a bridge patch installed. Cumpiano and Natelson use a bridge 3/8" high so there's some room for a reduction I would think?

Kim