Having a true, flat surface on the bottom of the billet is very helpful in the carving and thickness process. In short, the carving begins with 'scooping' out the underside of the top to an approximate contour. Then, flip the billet and work the outside of the top down to 'fat' thickness dimensions. Keeping fat dimensions, alternate the work on both the inside and outside of the top until the contour of each is acceptable. All that one wants to be thinking about up to this point is SHAPE.
Work down to the final thickness dimensions very slowly. Maintain a close check on the 8 or 10 spots that tell he thickness story...down the middle, across the mid-section and at the sound aperture (oval or f-hole).
There are many sources on-line with contour plans and/or thickness dimensions for both the top and back of the mandolin. I am using some very-well drawn and detailed plans of a Gibson A-3 from the early 1900s. They came from Georgia Luthier Supply. They're on-line.
Joining and Carving the Top
The picture above was taken this week (Dec 1, 2016). To get to this point I first selected a suitable spruce billet from the Woody Strings 'warehouse'.
The month of November flew quickly by. Activity in the Woody Stings shop changed focus. The plan for this winter now includes producing two mandolins, one A-style and one F-style. I also have two guitars started but, realistically, I will be surprised if I finish the guitars before June. Carving mandolins is the priority at the moment.
The billet was taken to a chopping block where it was split down the center with a 10" blade and a sledge hammer. The result is two book-leafed pieces of spruce which will be joined in the center to create what we hope will be an acoustically symmetrical soundboard, that is, the spruce grain on one side of the centerline will be a mirror image of the grain on the other side. Thus, the soundboard should transmit vibrations symmetrically from the bridge outward.
In the photo below, note that the quarter-split surfaces are flat, no twist... THIS is straight grain with no run out. A log can only split this straight if the tree grew tall, broad and straight, i.e. the growth rings are concentric with the axis of the tree and evenly distributed.
The key to carving: Be patient, don't expect to carve the entire top in one session (or even one day). There are many challenges to carving both sides of the mandolin top. Proceed slowly and you will see the challenges coming before you have to deal with them.
The story on the spruce billets in Woody's shop goes back to the early '80s when Woody lived in Alaska (10 years). The Sitka spruce soundboards for my mandolins come from SouthEast Alaska, Prince of Wales Island. In 1981, a friend, teaching music on the island at the time, invited me down from Fairbanks to help harvest some music-grade spruce.
Back in the day when Alaska was still a territory of the U.S. (1950s), logging-road bridges were built with the best materials available_ Sitka spruce. Large, strong trees were selected to be used as bridge stringers (structural supports).
In the '80s, when I visited my friend, the spruce bridges of Prince of Wales Island were being replaced with concrete. In the process, the spruce stringers were cast aside into the forest. A few people, like my friend the teacher/violinist, knew how to mobilize the right men and machines to retrieve these 36"-diameter spruce logs. My contribution to the 'harvesting' was to split mandolin/violin-size billets from the spruce rounds once they were under shelter back at the village. Pictured below are about 40 split billets from that adventure. This is music-grade spruce, now about 60 years since first harvested for bridge stringers. They have 25-30 gpi and are very straight. (see below)
Merry Christmas and Prosperous New Year !!!
Sitka spruce split billets.
Final word_ always support the work from the underside when carving, especially the points where the edges are clamped. Seen in the photos above are a carved-from-styrofoam cradle to put under the soundboard for support. A styrofoam board is easy to carve by raking it with a sharp drywall saw or a rasp. It makes a mess, but it's simple and it will provide the support needed while carving the inside contours.
The next step to producing a symmetrical soundboard is like carving the inside and the outside of a turtle shell from the same piece of wood. That's where I am right now.
Detailed plans, sharp tools, modest expectations and great patience help in carving the soundboard. It first needs to have a flat underside. This can be accomplished on various types of table sanders or with a drum sander and some carefully placed, and glued support blocks at the four corners. The soundboard passes under the drum with the face down.
The billet should be split down the center so that both of the resulting halves will be approximately the same dimensions. As one can see below, when I joined the two centers, the 'half' on the left was thicker than the 'half' on the right. No matter, the glued-up stock needs to be only 16-18 mm thick in the center. At the glue joint, the left and right halves of the split billet were about 30 mm and 20 mm thick respectively. After 24 hours of clamping, the spruce is ready for carving.
Luthiers talk of 'straight grain'. Pictured and explained below is what is meant by this term to a luthier. In the vise the spruce billet is posing for a picture. One can see the split line running across the butt of the billet.