Build Diary| Jack Spira | Ditson Style Part 2

I have been enthralled by Jack’s Ditson style guitars as the originals had a certain old world charm and in the latter years sounded rather good, especially with silk and steels. Their smaller size mean they could be played very comfortably with a quick response and an intimate tone.

My fate was sealed when I saw the 45 style replica pictured above. The little jewel of a guitar bewitched my eyes and senses and I began to plot a order from Jack!

We agreed on a set of specs which came very close to the originals with some modern amenites. They would have adjustable truss rods and also be X braced for light guage steel strings.

Jack has very kindly agreed to document the build process of a pair of Ditson style 1-45s: one in Brazilian rosewood and another in Acacia for us! So without further ado, here continues the build diary:

Please Click on the pics for fullsized view!

Time gets away! Nice to take up the Ditsons again after neglecting them during a busy period..

After the rosettes are dried, I can pull out the Teflon strip, which leaves and nice even 1.6mm slots for the shell to go into.

I’ve made several jigs over the years for cutting the fragile pieces of shell into curved strips. Happily for me a friend started a business a few years a go supplying shell, and cutting the strips. So now I can just order up Black pearl or Paua etc, in nicely machined 1.6mm wide curves. I like to use the short sections of solid shell still, rather than the laminated sheets. There’s nothing wrong with the laminated shell, it’s beautiful, and very consistent. I prefer the inconsistencies of the natural shell, and enjoy going through picking out the good bits for the rosette.

The sections of shell are fitted end to end in the rosette slot; each end has to be carefully filed to fit snug to the next bit.

Once that’s all done the tops can be run through the sander to flatten the rosette down flush with the top.

It’s particularly useful to have this machine to flatten a shell rosette, as the shell is much harder than the surrounding wood. Its impossible to cut the shell with any kind of blade I think, so grinding it down with sandpaper is the only way to shape it. This can be tricky, as the much softer spruce surrounding the shell will abrade much faster. It gets more difficult at the purfling stage, there being much more shell to shape around the edge of the guitar, plus the soundboard is close to final thickness at that stage. So when doing the shell purfling, it pays to install the shell very carefully to minimize the amount of final shaping needed.

Next I can do the fine thicknessing to the top. The Adirondack spruce is very strong, and the small soundboard is inherently stiff, so its quite thin, about 2.5mm by the time it feels right to me.

That done I can mark out the brace positions on the underside of the soundboard. Dick Boak from Martin guitar very kindly provided me with scans of the original bracing templates from the factory, so I can accurately know the positions.

This is a pic of the original martin template.

I just have to figure out how heavy to brace it. The Adirondack is very strong, and the top is very narrow, so I don’t brace very heavily, and find myself cutting more off the braces when I come back and look at it again a few days later.

I’m sticking to the original bracing for most of this top. As it’s a Blackwood guitar and so a departure from the original in that way, I’m using my own system for the neck block and upper bout area. I’ll stick to the original design for the rosewood guitar.

This A frame structure under the fret board in the upper bout is not an original idea, I’ve seen similar designs in many makers work. It does seem particularly effective at holding the neck block stable over the long term, greatly reducing the risk of neck angle problems as the instrument ages, and also seems very good at preventing cracks and failings in the top, especially along the edges of the fret board.

The sides bend easily. Blackwood bends well, even with this high figure, and the Ditson shape is not a difficult one to bend. I have to take care lining the sides up as I bend them as the pieces I’ve got are only just long enough… Its always the way! The best looking bits of figured wood are only just big enough.. Next up is to put the linings into the sides. So I need to figure out if i will depart from the original design again, and use my usual solid mahogany linings. Or stick with the martin design and use the kerfed linings…..

I’ll try not to leave it too long this time!

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