Saturday, April 7, 2012

Five-Course Mandolin Part 3

Carving the plates requires a certain kind of determination. This is the back, and I have used a router to remove a series of rings of material at varying depths to provide a guideline for carving. It's like a topographic map in maple. I'll use a small plane to take down the pointed areas of the terraces followed by a scraper.
You can see traces of the stepped profile remain as I further refine the curve. Still a lot of lumps and bumps. I've also started to carve in an indication of the "recurve", the area next to the edge of the plate that dips before rising again to resolve at the binding.

More scraping. It's easy to start chasing the lumps around. They disappear in one area only to pop up again in another.

Ready for hollowing!  I'll hold off on carving the recurve to its final depth until after the mandolin is assembled. The recurve of the back has a major effect on the tone of a carved instrument and it's best to sneak up on the optimal flexibility.

I embedded a dowel in the surface of my drill table that is centred on the bit and marked out some depth notations on the inner surface of the plate. By setting the drill stop at various depths I will give myself a visual aid in the hollowing process. To make measuring between bit and dowel easier I made up a little wedge of hardwood with increments of 1/2mm marked on it.  I left a generous amount for waste.

This is a quick-and-dirty carving cradle I whipped up. It's made from 3/4" (19mm) ply that is sawn out to a profile that supports the plate around its edge. I lined it with some scrap foam I had sitting around. This allows me to clamp the work in position. Carving involves some muscle and the movements are repetitive. It's especially hard work in maple, though spruce furnishes its own set of challenges. It's much easier to tear the grain of softwoods. In either case most of the rough carving is done across the grain. 
Like so.  I'm using a small convex-soled plane and various shallow gouges. The thickness profile was taken from a smashed 1950's Gibson I ran into quite a long time ago.  It's thickest right in the center and thins toward the edges, but not in a strictly concentric way. The area near the neck end is quite thick and it extends forward .  When I reach the bottom of the guide holes I start to pay very close attention to what is happening, making frequent checks with my thickness caliper.
I even got out my baby Ibex plane!  Isn't this ridiculous? It works well though, even if it is hard to hold on to. Curved scrapers finished the graduation and then a quick sanding with a random orbit sander.

Nice. It took some doing. The curved profile of the hollow extends all the way out to where the lining meets the back.  The top was carved using the same method.

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