Planning stage for 8 string guitar. SS

[Dave Bagwill]

I'm anticipating building an 8 string SS in the Spring. Lots to consider, of course, so from time to time I'll be bouncing ideas off the Collective Wisdom of the Forum.

First idea: what do you think of using the bracing scheme in the pic? It is of course the same wide-A bracing I'm using on the Odd Couple (putting the finish on it now). The advantage would be that, with the hole offset, I might not need much extra bracing to accommodate the extra tension from the 2 additional bass strings. Those 2 strings, btw, will be tuned (not fretted) to D and C, one and two notes below the normal E string. I'll be looking for low tension strings that sound good tuned that low.

Any thoughts on this first step?

[Dave Bagwill]

Okay, now that that's settled, here's a pic of a neck configuration that is close to what I'm considering. The 2 bass tuners in the pic are not situated the way I would like - since my plan is to have those 2 strings unfretted, the two tuners could be lowered to a more normal place. I will keep the 6 on a side setup for the regular strings. The plan in the pic is called, if I remember correctly, an 'unfretted harp guitar' or some such thing, the point being that the actual frets cover the whole fretboard but are not used for the 2 bass strings.

[TonyinNYC]

Hey Dave,

Since nobody answered your question, I will try. It is tough to say if a certain brace size will work for a given string tension. For me it is anyway. If it were a simple engineering problem, Ken Cierp would have a formula to punch the numbers into and out would come the idea top thickness and brace dimensions. But it is not that simple. My answer, however, is fairly simple. You are getting close to stringing up a guitar with the same bracing pattern. I would suggest you do that before beginning work on the sound board for the new guitar. If the top does not deform under the string tension of 6 strings, and you know how much additional tension you will be adding with the two harp strings, you can make a fairly good guess as to how the same bracing pattern will work with the extra tension. If you see any top movement when you string up the 6 string version, i.e. bridge rotation, top raising up too much, then you know you will need to add a little more strength to your bracing.
Sound good?

[Dave Bagwill]

Those were my thoughts on it as well. I know the A brace works well - Tacoma built a million guitars using it and they sounded very nice.
I'll be doing more research.

[ken cierp]

It’s been a long time since I communicated with Tom Ribbecke – yikes we were even using a telephone!! As some may know Tom designed (I believe holds a patent for) a tail-block door which allows access to the bracing and other internals. Seems like he did a lot of experimentation shaving braces while the guitar was up to pitch – pretty cool idea. Anyway Tom and I are not buddy’s or anything I just contacted him to get his take on a design I had for a 12 string cross over --- yes nylon strings. I figured it would have a Lute like sound that is really very pleasing to my ear. The experiment was going to be done using a “D” body, with an “X” braced sound-board, I had the rim already -- why not. So his thought was --- he did some calculation in his head and concluded or guessed, that the 12 high tension nylon strings would have about 20% more tension then a set of six medium gage steel strings. He suggested that I make the braces 20% taller. I never completed the guitar - might still, but that’s how I remember the recommendation. There are numerous string tension charts on the Internet so the calculations would be pretty simple.

[Dave Bagwill]

Thanks Ken. I've finally decided on an x-brace; there will be enough new stuff for me to get my head around without throwing in the A frame.
So I will look around for tension charts. I also need to find some heavy - maybe .060? - strings to use for the 2 bass strings, something that does not sound 'flabby' when tuned to C and D. I sound flabby no matter how I'm tuned.

[John Parchem]

Why C and D? Maybe G and B an octave lower than the open G and B. Using bass strings.