Slight warp in soundboard during construction

Construction and repair of Classical Guitar and related instruments
Ben K.

Slight warp in soundboard during construction

Post by Ben K. » Sat Nov 11, 2006 8:42 am

Hi Everyone,

I am building my first guitar and have a question for some of the more expeienced builders out there. I just finished gluing the grafts, finger braces, and fan braces to the back of the soundboard several days ago. I have attached a picture to show the current state of the soundboard. Just tonight, I noticed a slight warp, with the center of the soundboard bowing out very slightly (about 1/16" displacement). Until I braced the soundboard, I always stored it between two sheets of plywood to prevent warping, but I can no longer do this due to the braces. I have yet to attach the tranverse braces, one of which will actually pull the soundboard into a slight bow.

So my question is: Is this kind of warp normal after partial bracing of the soundboard. Maybe I am worrying too much about this.

Also, a note with regard to the humidity in my area (Austin, USA). The outdoor humidity ranges between around 50-80% and the humidity inside my apartment hovers around 40-50% and does not change very much.

Thanks in advance for any input.
-Ben
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MarkJ

Post by MarkJ » Sat Nov 11, 2006 12:31 pm

Assuming you dished out your solera to a 25' radius or so, thinned the soundboard from about the bridge patch to the edges of the tailbloch and lining in the dished area and "sprung-in" the fan braces - not pre-shaped to the curve, then I would not worry about it. When you glue on the lower harmonic bar it should even out a bit (preshape the contact side if your solera is slightly dished in that area). You will be glueing the trued edge of the sides with dentellones or kerfed lining and the top will be true to the solera on the contact edge. If the top is not sitting flush with the bridge area of the solera, you could probably put a few go-bars on the bridge graft to push it down flush when you glue on the sides (if you use a go-bar deck for clamping the braces - I made one out of plywood and use 1/4 inch dowells with cork feet for go-bars). But I'm not convinced that would really be necessary.

Also, your top looks way over-braced. I would peak the fan braces full length and ramp the ends from the edge of the bridge graft to the ends. Do that in stages, checking tap tone and compliance (stiffness). A local luthier in your area may be willing to check the flex of the top to see if the system is reasonably responsive and flexible.

Pepe Vergara

Post by Pepe Vergara » Sat Nov 11, 2006 5:22 pm

Ben K:
Whatever MarkJ said, I ditto. Other practical obervations are: 1) If you are doing this alone, get a book, a good book. Like Guitarmaking -Tradition and Technology and read it from beginning to end before you start even cutting the wood. DO not just start reading and start making at the same time. You will find that there is a reason for everthing said at the beginning, and if you have not read the whole book, you may miss some of the details. 2) The bracing does not really need to be structurally that big. If you have a guitar now, take a mirror and look inside it. Check how the bracings are shaped. In custom made high end guitars, you will notice that bracing are very thin, maybe not too tall, and shaped in a way that show no right angle. Although, some will have a triangular form. 3) By the tone of your question, I am not sure you used solera. If you did not use it, you must have used a concave dish or some other form of depression in a piece of wood to force/glue the braces in. 4) I would not worry too much about trying to thicken the soundboard with a variable thickness (it is your first guitar - you just want to get it done soon). At the time of finishing the guitar, you will have the opportunity to sand some of that extra thickness off. I kind of do a box tuning by sanding a bit here and there trying to keep the top of the soundboard even until I get the note or tone I prefer for that guitar. At this point, try to follow your plan only. DO not worry about tuning. Make sure you sand all your internal bracigs to 200 grit. The bridge plate could have been half of that thickess.

Pepe Vergara

Post by Pepe Vergara » Sat Nov 11, 2006 5:59 pm

Here are some samples of how I do it:
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Pepe Vergara

Post by Pepe Vergara » Sat Nov 11, 2006 6:44 pm

One more:
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MarkJ

Post by MarkJ » Sun Nov 12, 2006 12:36 am

Good advice Pepe. I like your braces - nice and clean. I am wondering what your bracing for a cedar top looks like - I have only used spruce so far (German and Engelmann), but I have a very nice AAAA WRC top I would like to use next. If you have some pics of braced cedar tops I would love to see them. Thanks

Pepe Vergara

Post by Pepe Vergara » Sun Nov 12, 2006 12:50 am

MarkJ: I use cedar bracing for the cedar top. I may be the only one. I got hold of alot of WRC for bracing that I have enough. I know may luthiers, including my friend German Vasquez Rubio uses spruce for the bracings. Spruce is better structurally, but I have that thing in mind about the woods being the same type and having the same module of elasticity. In general, I would not have a problem with using either one. I also like to have the reiforncement under the rosette to be cedar in spruce flamenco guitar. I like the visual effect. In fact, I have experimented with everything. I will try to dig one photo of a all WRC top.

Nacio: You are welcome. Anytime you want to get started, let me know. Or if you prefer, wait until I move to Granada.

Pepe Vergara

Post by Pepe Vergara » Sun Nov 12, 2006 1:08 am

Here is a pic of my first guitar (copy of Ramirez, all cedar). I have not done a cedar top in years.
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Ben K.

Post by Ben K. » Sun Nov 12, 2006 4:13 pm

Thanks for the advice markj and pepe. I have yet to peak the braces, but I will try to thin them down a some more before I do. I am following the Cumpiano book, so that is where I got the dimensions. I am not really familiar with a solera, but the Cumpiano book has you clamp the fan braces to the soundboard with flat cauls cut to the right length. Since this is my first guitar, tuning the soundboard will be a learning experience for me.

Thanks,
Ben

Pepe Vergara

Post by Pepe Vergara » Sun Nov 12, 2006 4:20 pm

Once you get into guitarmaking fully, you will find that Cumpiano's book missed some details. You can go to his website where he has addressed some of those.

MarkJ

Post by MarkJ » Wed Nov 15, 2006 8:52 pm

Thanks for the picture of the braced cedar top Pepe. Did you work from a plan? if so which one? How did the guitar sound?

Thanks again

Pepe Vergara

Post by Pepe Vergara » Wed Nov 15, 2006 9:28 pm

MarkJ: My first guitar was made exactly from a Jose Ramirez played by Segovia for 20 years plan. I did copy it exactly because my teacher asked us to do it. Other than some aesthetic aspects, the guitar is perfect. The sound is the sound of a Ramirez. Although I have made many guitars since then, I cannot keep one for myself, someone always buy them. So, that guitar is my current guitar. Most people who come to my shop want to buy that first guitar. The thing is, it is not for sale. Too many details were not perfect. Currently, I have my own bracing for every different situation. I think I have improved the Ramirez (uhmmm....!) bracing a bit.

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