Playing the Shell Game

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Back in April I cut and installed the headstock inlay for the parlour guitar, and wrote about the process for Furniture & Cabinetmaking (issue 236). What follows is an expanded version of that article.

The first task with any inlay is to select an appropriate design. I find that line drawings work best, as they give a clear indication of where the cuts need to be made, and ensure that the design is not overly dependant on engraving. I make multiple copies of the final design, and mark on the master copy the material which will be used for each element of the work. For the parlour guitar I chose a rose design, the stem of which is 1.5mm square sterling silver wire, the leaves are mother of pearl, and the petals are both green and red abalone, all set into an ebony headstock veneer on a steamed pear neck.

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Shell blanks can vary in thickness, which can make life difficult when it comes to cutting the recess for the inlay. So before I start cutting I check the thickness of each piece of shell with callipers, and any pieces which are too thick are brought down to thickness by sanding with 80 grit paper on a piece of 10mm thick float glass. It is important to thickness from the back of the shell, so that the show face isn’t worn though.

With the shell thicknessed, I glue sections of the design onto the shell using contact adhesive (this is why multiple copies of the design are necessary). Correct orientation of the shell is critical to a design translating well to inlay, and I always seek to arrange the design so that different elements catch the light from different angles. If the whole design catches the light at the same point then it will look stunning from that position, but dull from every other perspective. If light catches different elements of the shell as you move around the design, then it will look good from every angle.

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To cut the shell I used a Knew Concept’s piercing saw and No.2 blades, cutting right on the line and supporting the work with 3” wide piece of southern yellow pine into which a “v” shape has been cut. The saw blade moves within the “v”, while the shell remains supported on two sides, which keeps it from snapping. For cutting curves, the shell is slowly rotated, and the saw maintains a constant position.

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Those with ninja-level sawing abilities will be able to inlay shell straight off the saw. For the rest of us, a set of needle files is essential to refine shapes. I use the same birdsmouth support when filing the shell, and this helps keep the filed edges of the shell at 90 degrees to the show face.

Once the shell has been cut and refined, it is time to cut the recess. I glued another copy of the design to the work piece, and defined the edges of the recess with No.10 blade scalpel blade. This can be done either by tracing the edge of design, or around the shell pieces, depending on design. This ensures that the shape of the recess remains crisp and no more material is removed than necessary. For this design, I scribed round the line drawings, as there were too many small pieces to make scribing the outline of each piece of shell practical.

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If the recess is large I use a Lie Neilsen No. 271 router plane fitted with a 1/32cutter and the optional depth stop (which for this work is less of an optional fixture and much more of a necessity). This design was too small for the router plane, as the plane blade would have bruised the sides of the recess. So instead I used a Dremel in a router stand, and a 1.6mm down cut spiral cutter. Whichever method you chose, it is key that the recess be uniform in depth, placing the top surface of each piece of shell at, or just under, the surface of the wood. This is so that when finish sanding, the thin show surface of the shell is not sanded through, and that any film finish does not collect in hollows and obscure the inlay design.

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Wire is much easier to bend before it is cut to length, so I placed the end of the wire stock in the recess and guided the wire into the channel, bending it to shape. Once bent, I cut it to length and filed away the burrs.

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Gluing fragile shell can be a fraught experience, so I prefer to use a 24 hour epoxy with working time of at least 90 minutes. Epoxy can be dyed to match the surrounding wood, either using wood dust or filler dyes. For inlay set into ebony I use lamb black to dye the epoxy, adding it slowly until a good colour match is achieved. Ensure a good coverage of epoxy on the sides and floor of the recess, and then place the pieces in. On designs with a number of pieces in a single cavity, such as this rose design, I fit the interlocking pieces first, followed by any free floating pieces. The one disadvantage of epoxy is that it can be very thick, and so it is necessary to really press the shell into place (while taking care not to snap the shell) to make sure it is flat on the floor of the recess. I then left the epoxy for 24 hours to set and cure, and then sanded the excess back with 340 grit paper and a hard sanding block.

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The inlay is glued in and left to cure.

I’m pleased with how this inlay has turned out, and hopefully this post goes some way to demystifying the processes. With careful cutting, filing and routing, pleasing inlay is within the reach of pretty much all woodworkers.

2 thoughts on “Playing the Shell Game

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