Ukulele Bracing

[Samuel Bieber]

I recently repaired and started playing my grandfathers old Regal soprano uke that had been a wall hanger at my dads house for the last 20 years. It's been so much fun that it is obvious I need to build something a little higher quality. I picked up a used Martin S1 so I'd have something to look at and to my surprise the Regal sounds way better. The Martin has much better fretwork and intonation but the Regal is louder, has better projection, better bass and just generally a fuller sound. It also has no bracing at all top or back. I'm planning to build a koa soprano and a concert and am looking for bracing and top/back thickness recommendations. So much for just copying the Martin................................................

[Chris Reed]

Hmm, this could be a long post. I have Views on this topic.

But you need to know where these views are coming from. I'm a strictly amateur builder, ukes only, currently working on my 25th. All bar the current and one previous are soprano or smaller, and no two are the same. This is the smallest, half-scale (6.75 ins) made for a professional musician who is playing it in this video: http://www.youtube.com/watch?v=MZoN4LZfQrA

What I'm aiming for in a uke is what you describe for your Regal - lightness, volume, and a feeling that the whole instrument is alive in your hands. So my bracing aims at achieving that.

This is a recent soprano in koa. The body shape is narrow, 5.5 ins across the lower bout, which I guess gives about 80% of the soundboard area of a Martin shape. The back has a pronounced arch fore and aft - I haven't measured the radius but I'd guess it's between 4 and 5 feet. The arch is more pronounced than these pictures suggest.





This instrument weighed 220g (just under 4 oz) until I recently fitted better tuners, which probably add about 20g. If it had a mahogany neck rather than Spanish cedar it would weigh a fraction more. I'd say it's probably louder than a modern Martin soprano (but "loudness" is very subjective), though not as loud as most 20s Style 0s.

So, the bracing.

Top: a single spruce brace just below the soundhole, about 4mm wide x 6mm tall. Tapered from the soundhole edge down to nothing where the brace meets the sides. A bridge patch made from soundboard cutoff, about 0.5 ins wider all round than the bridge and with its edges chamfered and rounded corners.

Back: nothing. The narrow waist and the arch are enough to give the back the rigidity it needs. If you don't arch your back you will need at least one brace, which I'd put at the widest part of the lower bout. But I think an arched back really contributes towards the liveliness and volume of a soprano - all the flat backs I've made or played sound dull in comparison.

Linings: solid linings from side offcuts.

Thickness: all the body plates are a little under 2 mm, probably about 1.8 mm. But I don't measure precisely - instead I judge by how flexible the plate is. Longitudinally I want to be able to flex a shallow arch with light finger pressure. Laterally I'm happy with quite a bit of flexibility, but want to stop short of "floppy". So I'm trading these off as I do the final thicknessing. I've also found that plates sometimes have stiff spots, and I'll thin those further with a cabinet scraper until the longitudinal flexibility seems even.

Bear in mind that koa is highly variable, both in density and stiffness. So I'd take it down to 2 mm and then start flexing and scraping.

I'm currently working on a concert scale (15 in) cigar box uke, except I built the box. Spruce top and mahogany sides, similar approach to flexing. The tension on a concert scale is not vastly greater than a soprano but the top and back are of course longer and wider, and thus need a little more support. I've given this one two top braces fore and aft of the soundhole and two fans, which run from the points on the aft brace which are at the soundhole width 2/3 of the distance towards the tail at a bit of an angle (precision work, as you can tell). This has no bridge patch, but the bridge is about 3.5 ins wide, scalloped down from the ends of the saddle to its tips. The fans run under the tips of the bridge and are tapered from half their length down to nothing. I won't know how well this works until I string up, but it feels solid enough and the box gives a nice "boing" when tapped.

I hope this helps. If I wanted to sum up my approach I'd say it's "Build as light as you dare, then take a deep breath and make it a bit lighter."

[Samuel Bieber]

Thanks Chris,
That's just the kind of feedback I'm looking for. I'm a hobby builder as well with 15 or so guitars and a couple of mandos under my belt. Do you use a dish for the back radius?

[Chris Reed]

Not a dish, just a trough. A piece of 1/4 inch MDF screwed in its middle to a baseboard with battens under either side.

This avoids the complication of a go-bar deck (which I don't possess) and makes clamping easy. No signs of backs sinking, even without any bracing.