Bass Ukulele – Progress

Starting to feel like it might be finished one day!

Fitting the tuners

The neck is more-or-less finished. I’ve fitted the tuners (drilled out to take the larger strings) so that I could see what it all sounded like. The answer is that it sounds lovely 🙂

Strings on even though nothing is glued yet

I’ve had big problems making the nut. The first couple were the wrong way round. Then they split – probably because the grooves are too narrow and the string spreads slideways under tension, forcing the groove wider. Hopefully the next one will work.

Fingerboard over the soundboard

The fingerboard is made but I still need to finish the edges – I’ll do that when it is glued in place.

Tailpiece

The tailpiece is beveled so that the strings don’t have to bend too much. There is limited clearance under the tailpiece but they do fit without touching the soundboard.

Looking ok

Things still to do:

  • Work out where to put the F-holes in the soundboard
  • Fit the bass bar (spruce strip that runs parallel with the strings under the bass side of the bridge)
  • Work out how to make and fit a sound post
  • Fit an internal block to take the screw from the tailpiece string. I really don’t want the screw to give way!
  • Glue everything together. I’ve got some liquid hide glue so I should be able to take it apart again if I need to.
  • Finish the sides of the neck
  • Apply finish – probably some kind of oil.

Update 2021-05-25:

I’ve made the holes in the soundboard and attached the bass bar.

Soundboard with holes and bass bar

The shape of the sound holes was based on a couple of criteria.

Firstly I read somewhere that the key aspect to the holes is the length of the perimeter rather than the area. A longer perimeter is better for a low resonant frequency and volume of sound. I couldn’t follow the maths but maybe this is true for this instrument too.

The second aspect is that the sound holes decouple the centre of the soundboard (the bit under the bridge) from the sides of the instrument. This allows the centre to vibrate a lot more than it would be able to do if it was all joined together. My instrument is a box, so to get the maximum area of vibration it makes sense to put the holes close to the edge and keep them straight. The straight lines also match the aesthetic of the rest of the instrument.

The circular holes at the ends are to try to minimise any stress concentration when the board flexes, allowing a more free and progressive flex.

The bass bar is (cheap, DIY store) spruce shaped with a slight curve to arch the soundboard a few mm and preload the bridge area. The shape makes clamping it easy as I only need to clamp the ends. The bar is probably on the small size. The cross-section is a truncated triangle i.e. the width further from the soundboard is larger to minimise weight for maximum strength. I’ll need to trim the ends to allow the ends to flex a bit, but I need them square at this stage to take the clamps.

I’ve no idea whether any of this is correct but I think the sound holes look nice. Worst case is that the resonant frequency is higher than the lowest note and I get a boom effect on some notes. In that case I’ll need to increase the amount of flex in the soundboard to lower the resonant frequency. I’ve glued it all with (Titebond) hide glue so I can get it all apart if necessary.

Update 2021-05-31:

See this for a summary of the build.

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