In The Thick Of It

Dear Ron:
There are two loads you need to consider. The static string load, and the "plucking" load. Lets say your harp is shaped like a "C". The strings static load will try to close the "C", and the dimension of the neck, the side opposite the opening in the "C" (let's call this inboard), I think you want to call "thickness". In and out of the screen, I think you want to call width.
Width keeps the strings from folding the harp in "half" by pulling it into a spiral, and returns the strings to the position that fingers or picks will need to find them to play notes. 1-1/2" will probably be OK here, if you stick with wood.
Your first three strings, closest to the opening, when suitably tightened, will fail your 1-1/2" thick neck, and tightening the additional strings "inboard" will loosen the outer strings. So I'd recommend the cross section look something like this:
/| < | strings-> o o o o o o o \|
And / or for artistic effect, you may want to stick with a metal frame, or at least a metal reinforced neck. The sounding box components are most important, the neck is less so. You can possibly get less than 1-1.2" thick, and even use hollow members, if you want.
David A. Smith

Hmmm, like Alice, I try to learn six impossible things before breakfast.
But, you know, I never even thought of the shape which is actually swan shaped; the three lowest strings are at the base of the neck while the highest strings go upwards towards the ... "beak"... so to speak. I always thought the design was quite elegant, but then I hadn't started building one at the time. :-)
Ron

Dear Ron:
It will be a degree or two easier, if you move the high frequency, therefore tighter, strings towards the "neck of the swan". (Read "easier" as lighter, smaller.)
Elegance is to use your voice. Beyond this, is less elegance (or loss of voice).
David A. Smith

Thanks for the tip David but I don't know if it's applicable here; unlike with traditional designs, instead of using strings that go up/ down in thickness for the various notes, this harp just uses one size [electric guitar] string only. But I was thinking about using standard harp strings, and I may try them some day... :-)
Lol, people tell me that my voice is anything *but* elegant and I should stay far away from any American Idol auditions. However as for the harp, designer Wah Chang was a creative genius-- doing makeup and designing a variety of gizmos to be used as props for movies as well as TV shows like Star Trek, the Outer Limits, et al. I think his harp design was his best work:

but too few people appreciate it the way I do. Pity... :-)
Ron
------------------ "In the beginning was the rhythm; but I had forgotten and I was waiting for the word."
-- Ray Manzarek --

Dear Ron:
... It absolutely is.
A lot of older instruments use a single "grade" of string.
The frequency goes up with tension (for a fixed length). Putting higher tension wires further from the "neck", stresses the neck more, than if they were closer.
Its your free time...
David A. Smith

Well, as Admiral Kirk once said "We learn by doing..."
Ron