2 mins
An alternative rib construction method
An option that can guarantee an accurate overhang at the end of the process
Lutherie
In the course of my making career I have used various ways of forming the ribs: building up on a board, using an external mould, and having full or partial internal moulds. I now use a modified internal mould, which uses wood screws to hold the corner- and end-blocks in place, rather than the usual glued joints.
In the conventional method, the glued joints are broken to free the completed structure from the mould. With this modification I am able to keep the structure on the mould until after it is joined to the back. This facilitates an accurate overhang.
The mould
ALL PHOTOS ALAN BEAVITT
1 My mould consists of two parts, normally held together with four screws and captured nuts. For a violin mould, one piece is 8mm thick and the other 22mm. There are six holes drilled halfway down, which will accommodate the wood screws. I use selfpiloting wood screws with a Pozidriv head, which do not mind being screwed in at an angle.
Roughing out the blocks with a bandsaw
2 I start with a 30mm slice from a spruce wedge, and mark out the blocks with templates. For a corner-block I orient the template to have the annual growth rings pointing to a tip, whereas for the top- and bottom-blocks they are at right angles. I use a bandsaw to rough them out.
3a
Attaching the blocks with a wood screw
3b
Marking the outline
3c
Sanding the corner-blocks
3 I attach the roughed-out blocks with 3 wood screws (3a), and then mark out the definitive outline (3b). I use a reciprocating sander to finalise the outline (3c).
4a
Thinner section removed
4 With the sides glued in place, I can remove the thinner section of the mould (4a) and attach the linings using clamps made from wooden clothes pegs turned inside out (4b). The C-bout linings are tucked into notches which are already in place on the corner-blocks.
I can now mark out the rib structure outline on the back plate and, with the back finished, glue them together (4c). There is no need to manipulate the ribs to get the best overhang, and I can glue one bout at a time.Â
Gluing on the linings
4b
Joining to the back
4c
Releasing from the mould
5 Next, I remove the wood screws to release the assembly from the mould and, after fitting the top linings, pare away the excess wood.
The finished assembly
6 Here is the completed rib structure. The screw hole in the bottom-block coincides with the end-button hole, so there is just one hole left in the top-block. I am in good company here, as Strads with an original top-block have three nail holes!Â