A fishy tale of sound hole decoration

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The finished sound hole decoration, and sound hole

Progress on the parlour guitar has slowed a little since the Apprentice arrived, but I did find the opportunity to install the sound hole decoration this week. I had intended to work on the sound hole decoration at EWS, and to maximise the number of skills shown in the demonstration my decoration design was alternating blocks of ebony and mother of pearl between ebony banding. As it happened, I had no opportunity to do any work at EWS thanks to the level of interest from attendees. Since EWS I have been pondering the design again, and decided to revert back to my original design of a simple herringbone inlay. The corner purfling on the guitar will also be herringbone, so the matching sound hole decoration will avoid introducing another clashing element, which is particularly important on a small bodied guitar when the decorative elements are so much closer together. The previous design work was not wasted, as I was able to use the same spacing and circumferences as I would for the shell/ ebony design.

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Before I make any cuts to the soundboard, I always make a test piece using offcuts from the soundboard timber. This allows me to check the spacing of the cuts and ensure that the inlay fits before I make the critical cuts for real. The two edges of the trench for the inlay were cut using a rosette cutter from LMII, after which I removed the bulk of the waste with a Lie Nielsen No.271 small router plane. The depth of the trench is critical, as the soundboard is only 2.7mm thick and the herringbone inlay is a little over 2mm high. This gives very little margin for error, and I set the rosette cutter blade to just a hair under 2mm so that a small amount of the herringbone could be removed after gluing.

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With the bulk of the waste removed, I then fine tuned the trench using a 0.81mm mini chisel and small marking knife, both by Blue Spruce Tool Works. With these I am able to remove any debris from the two corners at the bottom of the trench, so that the inlay fits flush to the bottom.

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Bending the herringbone on a bending iron

The herringbone banding is very fragile and won’t bend without some gentle persuasion. I bent the herringbone to the correct radius on my bending iron, going very slowly to avoid the edge banding snapping, or (even worse) the marquetry de-bonding and scattering  pieces across the workshop. When bending thin banding such as this, the trickiest part is keeping the length of the banding in a consistent horizontal plane, as applying heat to just one side will encourage it to slowly corkscrew as it bends. This will result in an inconsistent pattern once the inlay is planed flush to the soundboard. Once the banding was bent to the correct radius I levelled out the horizontal orientation by placing the banding on the flat top of the bending iron and trapped it under a broad chisel for a couple of seconds.

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The banding is inlayed and ready to be levelled to the soundboard.

The banding was a good tight fit in the trench, so a final touch was to bevel the leading edges of the banding with a cabinet scraper. This eased the banding into the trench and ensured that the edges of the trench would not be bruised when the banding was inserted. The banding was glued in using Titebond Liquid Hide Glue, which had been warmed by leaving the glue tube in a jug of hot water so that it was less viscous. Ordinarily I mix my own hide glue, but hadn’t much opportunity recently. The Titebond worked well and I will certainly use it for future work. With a liberal coat of glue in the trench, the banding was placed in position and gently tapped fully into the trench with a small hammer.

DSC_0752I left the banding to cure overnight, and then planed the excess banding flush with my low angle block plane, followed by a small cabinet scraper. The scraper allows the banding to be taken perfectly flush without removing any material from the soundboard, which is critical given the thickness of the soundboard at this point – there is little opportunity for sanding or removing plane tracks once the soundboard has been thicknessed.
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With the decoration complete the sound hole was then cut to a 90mm diameter, again using the LMII rosette cutter and the blade set to the full thickness of the sound board. Next I will be writing about how I approach bracing the soundboard.

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Cutting the sound hole

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