DIY Sopranino Ukulele Part 9 – More front and sides

Moving ahead with the sides and front.

Got the join where the sides meet at the tail fixed with an inlay of walnut (bit of parquet floor tile).

Gap between sides cleaned up
Walnut inserted. Looks nice!

I’ve started fitting out the soundboard.

Drilling the ends of the ‘f’ holes (Lidl Parkside wood drill – very good!)
Drilling from the other side to avoid tear-out
Cutting the straight bits of the ‘f’ holes

The saw wandered on one cut so I finished the cut with a knife and had to tweak the shape to hide the damage.

Spot the change to shape!
Ikea shelf supplying quarter-sawn wood for braces

This wood isn’t ideal. I think it is Scots Pine – nice wood but it is hard to work.

Gluing blank brace – cut to shape later
Started cutting braces to shape

I’m making a guess at a good brace position. The braces have to take two forces:

  1. The pull of the strings trying to move the bridge towards the neck. The top is probably plenty strong enough to resist this pull as long as it doesn’t buckle – there is no big soundhole between the bridge and neck. Here the braces just help stop the soundboard buckling.
  2. The bridge is trying to rotate – the string anchors are pulling out of the top and the saddle is pushing into the top. Here the braces must stop the bridge rotating the top, especially as the bridge is isolated from the sides by the ‘f’ holes.
Forces on the bridge

I’ve chosen to route the braces diagonally to provide some cross-grain stiffness (remember those ‘f’ holes – I don’t want the top flopping around) and it also makes them shorter so I get more area unbraced.

The objective for the bracing is provide the right amount of stiffness while having very low weight. I’ve no idea if I’ve got this right – we’ll see (and hear) when I’ve finished…

For the record, the braces are about 3mm thick and about 12mm deep under the bridge, tapering down to nothing at each end. I might take them down to 10mm deep under the bridge.

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