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Instrument Making School - Lecture 7, Inserting the Upper and Lower Ribs The next step is to insert the upper ribs first. Follow the contour of the lower blocks and bring edge of centre bout to what is called a "knife edge" using a chisel (Photo 7A). This should be completed for all four corners.
Figure 7A - Knife Edge Square top and bottom block to the inside template (Photo 2B) pencil marks. After squaring the corner blocks and the top and bottom blocks profiled and squared, we are ready to make our cramping blocks. You will need two "cramping" blocks for the lower corner blocks, two for the upper corner blocks as well as one for the top and one for the bottom (See Photo B for examples of a corner and bottom cramping block). The cramping blocks are used for cramping the ribs in place. These can be made from any suitable wood with poplar wood being preferable. The cramping blocks are made so they complement the blocks of the mould to form a square. It can be compared to a male-female joint.
Figure 7B - Cramping Blocks Bring out the ribs for the top bout and ensure the flame runs in the right direction as marked out (see previous lecture). Now we will bend the ribs for the top bouts. We now have the opportunity to perform a "dummy run" of an accurate join, which is crucial for the bottom block. We will "practice" this on the top bout as this does not need to be so clean and the top bout takes the neck in and will be cut out. Now we will need to square the top ends that will form our join on the top block. This can be achieved by "butting" the two ends. Using a flat surface, place the top ribs on edge and with a sharp block plane (set finely), square your ends to a very accurate join. This join will be glued in once the ribs are bent to the contour of the mould. When measuring this, allow 5-10 mm overhang on the corner blocks which will be trimmed later. Professional violinmakers generally don’t perform the previous procedure. Usually the bottom ribs are glued to the mould first as per photo 7C. As a beginner, please follow the procedure as outlined below. Bend our top side ribs as in the previous lecture. Take your time and don’t burn the ribs and get the ribs fitting as accurately as you can to the mould. See Lecture 6 on using a bendig iron. When the ribs are bent we will resume to glue the ribs. Starting with our top bout which we have already practiced joining, we will glue and clamp that part first using our cramping block as per the photos below. We need to make sure that the join is fully pushed in and cannot slip. Now we will glue our corner ribs, taking care not to dislodge the existing clamp. Glue both corner ribs using our cramping blocks (See Photo C), making sure everything is flat and with no gaps. It is advisable that you have a "dry run" with this (no glue).
Figure 7C - Clamp Bottom Ribs Allow three to four hours for drying and you should be left with the ribs in place and with overhang on the corners after the clamps come off. The overhang on the corners should be trimmed back and squared to our "knife edge" as crated before. If this is done correctly, it should be an invisible join. Repeat for the bottom.
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