I built a couple with spruce tops I couldn't use for other instruments. They came out sounding good. I think I made them 1/8" thick but I don't really remember. I should write this stuff down! I had to brace them too. Pretty large box as I was trying to get the bridge a little more forward on the box. Here's a pic during construction of one of them
I build most of my instruments using 1/2 cm (5 mm) thick wood for the sides and 2 mm thick plywood veneer for the sound board and back board. As I recall this is a bit thinner than the dimensions you mentioned above, and I consistently get better results than most cigar boxes I've tried. I think that with the dimensions of wood you have access to, that you also should be able to get pretty good results. However, like me, you should scout around for the thinnest material you can find for sound board and back boards. You might also look for someone who has a planner machine to use to thin down the 1/8" thick wood to maybe 1/16th. But remember that the thinner the wood, the more likely you will need to add additional bracing. I'd say go ahead and build with what you have, then on subsequent builds you can experiment with thinned sound boards and internal bracing, if needed.
P.S. I like the 'splated cbg2.jpg' file that Terry Harris posted. Some interesting concepts. Reminds me in part of the "thin box" design I have been experimenting with. It seems to me the thinner box sides will yield a crisp/clear sound, but that thicker walls will yield a more mellow tone. If anyone has had similar observations, I'd like to hear about them.
Thanks for your input Rand. I actually finished this build a couple of weeks ago, and went with the thicknesses mentioned in my first post. Here's a picture of the finished box:
Everything seemed to go fairly smoothly. The whole box is solid spruce - cost a small fortune but definitely looks the part. The finger joints were a a bit tricky but with a bit of sanding and they look pretty neat. The join on the top and bottom was surprisingly easy to achieve using the trick on the 'joining the top' movie you mentioned at some point before! I did use a bit of bracing across the underside of the soundboard.
Here's the finished guitar - definitely the best sounding and playing so far - hence why I'm still playing it rather than starting immediately on the next one!The next time I order wood, I'll try using 2mm spruce for the top and back, although I'm guessing what this will add is volume, which this build doesn't seem to be lacking, at least for home use!
Good job! That box looks really beautiful. The finger joints and solid wood make it look classy.
I need to locate sources for solid (as opposed to plywood) sound boards. I was thinking I could machine down some fir from a fence that we've recycled at the wood shop club that I joined this past year in the States, but them I'd need to butt join two or three thin cut boards to form the sound board as you did on your box. It can be done, just prefer not to have to do so much work. But I will have to wait 8 more months till I'm back in the States to try that. I did build some instrument "frames" which I will complete here in China. They are paddle box dulcimers that I machined from 1.25" by 1.25" lengths of red oak. I have high expectations for them. When I'm done I will write up some article on these builds and post them here on this CBN group. I'm just back in China and can't sleep because of jet lag.