Top Bracing

[Stilts]

Hi all,

I'm a bit of a newbie to the world of acoustic instrument building. I've built a few electrics before, as well as having done some general repairs, but my most daring acoustic venture was a little box ukelele made from meranti some years back
With a little more experience under my belt now I thought I would take another little baby step and have a go at a steel stringed cigar box guitar this time. The idea is something like a octave mandolin or bouzouki (8 strings), but the string pairs will be tuned in octaves.
Now, here's the question
For the top and bottom, I've got some nice Australian rosewood that's a little over 5mm thick. I plan on using fairly light strings on it, but would the string pressure require some sort of bracing?

Thanks
Miles

[Nick]

I've only built one cigar box guitar to date but just from that experience I'd say that it very much depends on what size you intend making your box. Obviously a smaller box will have a stronger lid as there isn't a large surface area to flex under string tension. Also the thickness you make the top will determine if it needs any extra support too. Cigar Box guitars were/aren't known for their acoustic properties and are better with some form of pickup system & amplification so if you have an 'average' sized box (175mm x 230mm (7" X 9")) and kept your lid thickness between 5-4mm ("standard" cigar boxes use a ply lid that comes in at 4mm and hardwood lids (used on paper covered boxes) about the same) I can't see you would need any additional bracing. These things have such a low bridge too that even strung as a Mandolin with the extra string number, I can't see there being a huge amount of downforce at the bridge. Plus if you make the lid removable or hinging, you could always add some bracing if the top looks like it wants to collapse or flex too much once strung up?

[Stilts]

Cigar Box guitars were/aren't known for their acoustic properties and are better with some form of pickup system & amplification so if you have an 'average' sized box (175mm x 230mm (7" X 9")) and kept your lid thickness between 5-4mm ("standard" cigar boxes use a ply lid that comes in at 4mm and hardwood lids (used on paper covered boxes) about the same) I can't see you would need any additional bracing. These things have such a low bridge too that even strung as a Mandolin with the extra string number, I can't see there being a huge amount of downforce at the bridge. Plus if you make the lid removable or hinging, you could always add some bracing if the top looks like it wants to collapse or flex too much once strung up?

The box size is set to be something around 250mm x 350mm, and I want to build it as a purely acoustic instrument (I know it won't keep up with an acoustic guitar but I just like the sound of them). Like my last one I'm also making a fully enclosed box rather the hinged lid, so any internal structuring needs to be done prior to assembly rather than just an afterthought.

I'm also toying with the idea of nylon strings to eliminate any reinforcement needs. Has anyone built or played/seen someone play an instrument with octave paired nylon strings? Google yields little in that area

[Nick]

I'm guessing ( and it would purely be a guess!) that nylon strings wouldn't have enough energy to drive a top of that sort of thickness, you'd get even less volume out of it than an unamplified steel version. Nothing to stop you trying it first though, you can alway switch over to steel strings if the nylons don't pan out. You could also go over to the forum at cigarbox nation and ask or search over there, those boys are plying with these things all of the time and would be far more knowledgeable than my guesswork!

[Allen]

I've worked on a couple of 8 string tenor ukes for clients, with octave pairs on the G,C and A. Unison on the E. Tops were thick in my opinion, and the bracing was over done too. They sounded dead un-amplified.

[Gerry Coon]

Good Day Miles,

You might like to have a look at Gadsden Guitars Facebook page. Gadsden makes a properly braced and arched box guitar well worth a look. Hope it helps. Good luck with yours.

Cheers.

Gerry

[Taffy Evans]

Hi Miles, I have built quite a few CBG's, and have used bracing on a ceder top. I did many trials to get good/better tone and volume, playing with bracing patterns and sound hole sizes. I think I nailed it in the end. Very loud for the size of the chamber. I did not think about strength so much more on tone and volume. If I put a magnetic pick up in the top that effects the acoustic quality so a I use different bracing for different models, especially on the six stringers.
What I like about these guitars is the freedom [lack of rules] just get in there and experiment.