#1
This build has quite a long back story, so please bear with me. First, let me say that I have no prior experience building guitars; I have a reasonable amount of experience with electronics and electric guitar repair, but I have never repaired an acoustic guitar, and my only experience with acoustics involved destroying an old child-size acoustic to look at the inside construction.
A few weeks ago, I started out building a guitar for an event at the state Science Olympiad this March. The guitar would have to be audible without amplification, so I was leaning towards a hollow-body design. My original designs featured a hollowbody electric fashioned out of two poplar boards, one for the top half of the body and the neck and one for the back half of the body.



I was planning to route out the insides of the two halves to hollow the guitar, but after an hour with a dovetail bit, it became apparent that this is easier said than done. Because I don't own the tools to tackle an ambitious build such as a guitar, I'm working with my neighbor, who is a retired contractor. While I thought about how to redesign the poplar guitar, he went off to rummage through some old wood he had in his basement, and returned with a few pieces of mahogany. It turns out that he happened to have this mahogany lying around, which had been in his basement for the past 20 years and took the form of a door from a Cape Cod house before that. We don't know how old it is, but there's a good chance it's 80-100 years old or more. Acoustically, it was spectacular; a highly irregularly shaped piece that formed the center of the door resonated better than the carefully shaped and tuned oak xylophone bars I had made a year ago. He had just enough to make a small-ish hollowbody.
I decided that if I was going to use the mahogany, I would make a guitar worth playing. This meant that I had to completely scrap my old design and re-draw everything from the bottom up, and introduced many technical difficulties I had previously avoided. Some of these I have been able to solve, but others I'm still working out. Remember that I have never built a guitar before, and am responsible for the design of the guitar without any templates or books or anything. Many aspects of this guitar are inevitably going to seem odd, as I frankly have no idea what I'm doing.
With all that intro out of the way, here's what I've done so far.


The aforementioned center piece, which will be turned into a neck.

All of the structural pieces (which formed the center, sides, top, and bottom of the door) were prepared for use by sawing off the unusable edges, ends, and bevels. There were two 1/4" thick panels which were sawed in half, bookmatched, and glued together to form a top and a bottom piece.


A template I made out of some particle board, on top of my Laguna LE400Q.


The prepared structural pieces were laid out over the template, cut and glued together to form the basic shape of the sides of the guitar.


The sides after saber-sawing out the inside profile, sanding and smoothing, and filling in the sharp edges.


The back piece was cut out first. Using the template as a guide, I saber-sawed the rough profile of the guitar, leaving about a quarter of an inch excess. Then, the template was clamped in place, and the final shape was routed out using a template bit. The profile was then traced onto the sides, and cut out to 1/4" with the saber saw.


Then, after drilling pilot holes, 4 finishing brads were used to secure the bottom to the sides. The bottom will have to be removed after the competition to install the electronics, and then it can be glued in place. Again using the template bit, the sides were routed to match the bottom piece. This took two passes, as the bit wasn't quite long enough to cut all the way through the piece.


The router snagged a couple times, ripping out a chunk of wood at the bottom and the top of the guitar. This was my first time using a router other than when testing out the dovetail bit on the original design, so I think I did pretty well. These portions will have to be filled in.


I haven't glued these in yet, but I also cut out some bracing for the bottom piece. These are 1/4" wide, 3/8" tall, and rounded off on the top (slightly). Since the panels are 1/4" thick to begin with, I figured I could get by with minimal bracing.


I won't go into details about the shape of the guitar, but it's going to be approximately 2 7/8" thick. Size was limited by the amount of mahogany I had to work with. The piece I have to cut a neck from is about 3 1/2" wide, 1" thick, and longer than I need. I already cut the headstock, 8" long and at a slight angle.


I ran into a lot of problems when designing this guitar, most of which have not yet been resolved, or at least not completely. The biggest problem that I knew I would face was the tuning mechanism- since no parts designed for musical instruments are allowed for the competition, I had to come up with a reliable way to tune the guitar without using commercial tuning pegs. I settled on a lever mechanism, similar to the fine tuning mechanism on a Floyd Rose tremolo bridge except with a smaller ratio. I'm planning on attaching a temporary unit that makes use of this mechanism to the back of the headstock until after the competition, when it can be removed and "real" tuning pegs can be installed.

Another major problem that results from the competition is that electronics, pickups, jacks, pots, etc. need to be installed after the competition. I was thinking about wiring a piezo transducer and a humbucker as bridge and neck pickups, using a dual-ganged pot to select between them, a volume pot (how many ohms?), and a push/pull pot as a tone/coil tap control. I want to keep the number of knobs at a minimum. Also, I have a stereo endpin jack, so I could wire the piezo to, say, the left output and the humbucker to the right as a means of splitting the signal. What do you think? Also, what pickups do you suggest? I'm looking for something as versatile as possible for the neck position.

Another thing I've been having problems with is the neck. I'm planning on using the one piece of mahogany for a one-piece neck/fretboard. I know that mahogany, especially this mahogany which is pretty soft, is not an ideal choice for a fretboard, but I was thinking about using some kind of an epoxy-based finish, or something else that's really tough. Any ideas? For the truss rod, I cut a 1/4" wide slot about 3/4" deep into the back side of the blank leaving about 1/4" for a fretboard. I'm going to cut a piece of 1/4" thick red oak as a sort of spacer to force the rod to bend. I think I'm going to make the neck heel-adjustable, so I don't have to fuss with the odd angle at the peghead. My neighbor has a relatively large router bit that I could use to do the preliminary shaping of the neck, before going over with a hand planer and lots of sandpaper. I think I'll leave the fretboard fretless for the time being, and slot and fret it after the competition so I can do whatever sort of inlay work I want.

I have two main questions concerning the acoustics of the guitar. The first is, how much do the braces really matter? I mean, I know that they will affect the sound, but is there anything that I should definitely avoid? Using non-scalloped or parabolic braces isn't the best idea, but I could still scallop them or shape them if it would really make a big difference. I think I'll use two lateral supports on the top that would give something sturdy for the bridge posts to secure to, and maybe a couple of supports spanning the width as well.

The other big question I have is about the sound hole. I always thought that the sound hole projects the sound waves, but after doing a little research I found several sites claiming that the sound hole mainly affects only the acoustical properties of the soundboard, e.g. how it flexes, its tonal properties etc. If this is the case, I was thinking about either cello-style f-holes on either side of the bridge, or two thin sideways-D-shaped holes on either side of the bridge instead of the traditional sideways S shape. What do you think?

Also, regarding the finish, I've been experimenting with some shellac and some spray lacquer on some pieces of scrap mahogany. Do you think that the time and effort that goes into a french polish is really worth it, or is it better to go for the durability of a lacquer finish? I don't mind refinishing a french polish, and I would rather have a finish that's easier to repair but I'm worried a french polish might put the wood itself at more risk of damage.

I'll post updates when I can, but I'll have school over the week so I wont get much work done except on weekends. Comments, suggestions, questions, criticism, (and most of all answers) are greatly appreciated.
#2
Ok so that was a lot of reading. but i can offer some advice regarding your questions. Braces are very important, the top is pretty thin and has a significant amount of stress on it from the pull of the strings. The top needs to vibrate to produce sound. If the braces are to thick and stiff you will have a strong top but the vibration/ tone will be negatively affected. At the same time if they are to thin the top will be more susceptible warping over time. The art of it is finding that perfect middle ground in between too thick and too thin. I not sure if you meant using supports that go from the back to the top to support the bridge but if you did its not such a good idea because it will probably make the guitar to stiff.

As for the sound holes, I'm not sure what you mean by the small D shaped holes (a quick sketch could help), but you cant really go wrong with f holes, they almost always look pretty classy.

Hopefully this helps a little bit. Good luck with the rest of the build!

-Tyler
#3
Thanks for the advice. No, I didn't mean supports spanning from the back to the top of the guitar, I was talking about parallel supports that would run from the neck to the bottom of the top, passing underneath the pickup bracket and the bridge posts. Although I did stumble upon this article: http://en.wikipedia.org/wiki/Sound_post and this article http://en.wikipedia.org/wiki/Bass_bar which sound appealing to me, mostly because I am in awe of the ability of violin-family instruments to project a very loud sound out of very small instruments.

I'm attaching a drawing I did in a couple minutes in Paint that might help demonstrate what I meant by the D-shaped holes. It's a bad drawing, so it doesnt look too good but you should get the idea. The design is based on the assumption that the holes exist to aid in the vibration of the guitar top.

Thanks again!
Attachments:
D-hole for guitar.png
#4
That article is pretty interesting, I may have to do more research on that and see how It might affect the sounds of an acoustic. And its not like its glued in place so testing it wont mess up a good instrument if it does not work.

Those holes don't look bad at all, I initially imagined a more literal and fatter D but I think those would work nicely. I'm still partial to F holes but the D would give it a more unique look. Either way you'll end up with a good look so do what you think looks best.