8 String tenor uke bracing advice

[Jim]

I'm planning an 8 String tenor ukulele build and thought I'd pick the brains of the forum for a starting point on bracing. I'm using some nice stiff bunya for the top (not thicknessed yet). Can anyone give me any thoughts on top thickness,brace dimensions and bridge plates for a starting point? It will be strung gG cC ee aa.

Thanks

Jim

[Allen]

You've doubled the string tension, so plan for that. Remember the cube rule for stiffness. You can achieve that through the top thickness, or the braces, or a combination of both.

[Jim]

Thanks Allen,
Is there a preferred method? I was thinking of doing both... ie top a little thicker and heavier bracing.
Jim

[Allen]

It really depends on what your usual is. If you are using tops at 1.8mm thick, then I'd make it thicker. If you are at 2.0 then that might be good, or you might want to beef that up a bit too. Those numbers mean nothing though until you have your timber in hand.

Or you could modify the bracing pattern to support the soundboard more with more braces but everything else being the same.

I don't build anything by the numbers. Each soundboard is judged on it's stiffness and species. Some will move around a fair bit on you with that much tension, others will take it without any worry at all.

Never built with Bunya, so have no advice at all about it.

[Jim]

Thanks Allen, your advice is much appreciated. I'll make it 2mm and play the bracing by ear.

[blackalex1952]

If you search this forum you will find all sorts of posts about scaling instrument size. The work of Craham Caldersmith regarding different instrument sizes is interesting, along with some of the discussions about bracing for different types of 12 string guitars, and also acoustic basses. You might also investigate deflection testing. I have a couple of deflection measuring set ups using gauges which are not too expensive and are also available on ebay and other second hand sources. I use a 1kg weight. There are posts on this forum on the subject as well. It is worth measuring the stiffness of the timbers you are working with. Factors that you are changing in comparing a smaller body size to a tenor size are: scale length along with the double string courses and associated string tension, soundboard size therefore the span of the braces and the soundboard, the brace heights and soundboard thickness, and with the lower string tuning on a tenor build and the larger soundboard and body, the associated resonances to make the instrument efficient as a sound producer. With an eight string build, you will also be changing the bridge and bridge plate with a change in bridge size.This would result in a heavier bridge. Bridges need to be as light as possible so bridge design is something to consider also. Cheers, Ross

[Jim]

Wow Ross thanks. Lots to take into account! I'll look into those scaling discussions and deflection testing.

Cheers

Jim

[mooshalah]

Hi Jim.

If you look at the recent "Gallery" postings, you will see that I've recently posted some photographs of an 8-stringed tenor ukulele that I made last year. This started out as a 4-stringed instrument, but I decided, once I'd already braced it and glued the body together, and added the neck, that I wanted to make an 8-stringed instrument.

I used a very stiff piece of Blackwood for the top, and it was thicknessed to a nominal 2mm (the edges are probably 1.8 - 1.9mm), and I'd already added:

A 1mm hardwood bridge patch.
Three symmetrical spruce fan braces, 4.5 mm wide X 8.0 mm high;
Two spruce top braces (above & below the sound-hole), 6.0 mm wide X 10.0 mm high;

I asked others (see a previous thread) for their opinions. Some recommended caution, while others said that I'd already made the braces too large for even a 4-stringed instrument.

After receiving this valuable and sage advice, I decided that I'd just "go for it".

The instrument, as built, seems extremely solid (but hey, who knows what the future will hold?) From past experience with other guitars and ukuleles, I'd say that this will be fine.

The sound is very lively - brash, even - and I don't see how it could be any better. If this were a classical or flamenco guitar, I'd be feeling all tender and unsure that the instrument was as good as it could be, that it would last over time, or that it conformed to some preconceived ideas of how a competent instrument might sound.

But this is a ukulele - and an 8-stringed one, at that - and I refuse to become all introverted and choked up, wondering whether it conforms to some ethereal, idealized concept of how an 8-stringed ukulele ought to sound, and whether this one cuts the mustard! I'm very happy with it, and that's what counts!

Thus, my opinion and bottom line:

2mm for a stiff piece of Bunya is fine;
Bridge patch and braces, sized as above, will be fine too;
You'll need to make the neck a smidgeon wider, to cater for the extra strings;
Think about what sort of tuners you're going to use; weight, length of headstock (aesthetics and balance), ease of tuning (twice as many knobs to turn);
Consider how to attach strings to bridge; because the forces are not that great, you can afford to be a bit innovative, and not necessarily use a tie-block or bridge-pins.

Regards,

Frank.

[Jim]

Thanks Frank,

That's a great starting point. I remember seeing yours in the gallery- I hope mine turns out that well! That's about what I'd decided for the braces- thought I'd start there and rely upon intuition (ha ha for a novice) once I had the top in my hands. I've been using a bunya bridge patch previously with the grain perpendicular to the top, I'm hoping this will do the trick again.
I was planning to have the neck width at 40mm at the nut- is this about what you had?

I'm only making this one for myself so I'll guess I'll see how the bracing goes as time ticks by.

Cheers

Jim

[Jim]

Well a progress report- it's almost done. I went with a 2mm top and braces are 6mm wide by 8mm high, three fan braces.
I've just got the bridge, saddle and nut to go, plus lots of sanding then finishing.
Two last questions- Does the bridge need to be bigger than usual? The practical considerations of fitting extra strings on aside. ie Does the pressure brought to bear by the extra strings necessitate a larger size?
and....
I haven't settled upon string spacings yet. I've gone with a 40mm nut width. Anyone have any firm opinions on spacing?
Thanks again for all the help.

Cheers
Jim

[Allen]

Other than the bridge being a bit larger to accomodate the extra width at the saddle and string spacing, I don't make mine any larger.

[Jim]

Great Allen thanks!