Violin Making Workbook
When joining the top, select a prominent grain line as the center, and, sighting down the length of the top at an angle, draw a pencil line down the course of this grain line. Find that same prominent grain line on the other half of the top and mark it with a pencil as well. Check the height of each down the length of the line with a thickness caliper. Insure that there will be sufficient height for both the fullest portion of the longitudinal arch and the width of the arch (width of the bridge feet) after the two halves of the top are flattened, joined and glued, and then flattened again.
Now bandsaw off the center portion (outside the grain line you've identified and highlighted in pencil) to use as a bass bar on another instrument. (Terry doesn't use wood from the same piece to make both the top and the bass bar.)
Continue joining the top as outlined in the section "woodworking - back".
insert illustration here
The outline drawing above shows the areas of the top where you want to maintain the full width of the cross arching, and the full-height width through the center of the plate for the fitting of the bridge feet. It also shows the transition areas from the C-bouts to the upper and lower bouts where the arching work maintains a line parallel to the grain lines of the top, with very little inward scooping.
When arching from the full center section out to the edges in the upper and lower bouts bouts, try to keep the lines straight (when viewed in profile from the ends of the plate) or just ever so slightly convex. Guarneri (Joe) had almost no channel to speak of. His arches ran full, right to the edge of the plate, with just the slightest dip over the purfling.
Final arching and graduation of the top plate is done after the ffs are cut into the plate. One of the advantages of this method is the ability to fine tune the arching to fit the ffs to the longitudinal profile of the of the plate. Another advantage is the ability to leave the borders around the ffs thick (from the inside) when completing the graduations. This precludes a player from automatically dismissing the instrument at first glance because the plate appears too thin when viewed through the ffs.
The plate is mated to the rib structure with the pins and spool clamps. The rib outline is marked (pencil or scribe?) on the plate, and the rib structure removed. A pencil is then used to mark the proximal borders of the neck, bottom and corner blocks (after trimming), and a border is drawn for the linings and rib thickness.
The plate is clamped into a padded cradle with cauls across the neck and bottom block locations. An arching gouge is used to rough graduate the upper and lower bouts to a thickness of 4mm. The center section is thicknessed to 5.5mm.
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The above illustration shows the rough thicknesses for intial graduation.
Laying out the Location for the ffs
(more needs to be added here re: use o the compass/divider for ff location)
TMB has plotted the mathematical relationships between the ff location and the edge of the plate, size of the plate, etc., for all of the Guarneris that have fallen into his hands. While the placement of the ffs on Guarneris can appear haphazard, they all share the same mathematical ratios. The superior border of the lower lobe will be even with the superior border of the purfling in the recurve (lowest point) of the lower corners. A flexible ruler laid across the arch from one purfling border to the other will give you the location of the upper-most margin of the lower lobe, and hence the longitudinal location of the ffs on the plate. "But wait," you say, "we haven't put the purfling in yet. How do you expect us to use a landmark that isn't there?" Don't get smart with me boy. There's a way to figure this out.
Set a divider with the legs far enough apart to just clear the thickness of the top plate in the lower C bout. With the top pins in, and the top held on to the ribs, set one point of the divider on the rib at its lowest point in the recurve (adjacent to the lower corner). With the other leg of the divider extending over the edge of the top you can use an awl to make a single mark at this location. Do the same thing on the other side. This is the theoretical location of the upper border of the purfling - it may vary depending on the amount of inset you plan to use. (Look, just do the math, OK? You know where the rib is going to be, and you know how much overhang you want, so subtract the amount of inset and adjust the marks accordingly.) Now, connect the dots with a flexible ruler, make a very light pencil mark across the lateral margins of the plate and you've got your superior/inferior landmark.
With this line established lay your ff template on the plate with the upper border of the lower lobe (that's "the superior margin of the caudal meatus" for those of you following along in your anatomy texts, or "the top of the bottom hole", for those of you with advanced degrees) on the line. Get the template lined up so that the inner edge of the connecting bar is roughly parallel with the center seam. Now, very lightly mark with a pencil the inner most (proximal) border of the upper lobe, and the inner border of the connecting bar, just above the notch. Do this on both sides (bass and treble). Now use the divider just as you did above, and mark the rib location at the edge of the plate lateral to these pencil lines.
Now grab your compass, make sure the lead is pointy, and strike off an arc (lightly so you can easily erase it) from the purfling border to the inner margin of the connecting bar above the notch. Do the same thing on the other side. Now measure the distance over the middle of the arch between these two compass arcs. The distance needs to be 70mm. If it's not, adjust the spread of the compass legs, erase the first set of marks and do it again. Keep doing this until the distance over the arch is 70mm.
Do the same thing with the inner margins of the upper lobes. The distance you're shooting for here is 40mm.
With these three points delineated (superior aspect of lower lobe, distance between connecting bar, and distance between upper lobes) you can place the ff template on the top and lightly trace its shape. Stand back and admire your work. Correct any asymmetries.
The lobes are drilled with a hole saw. I like to use a circle template to find the center of the lobe to drill the pilot hole. Soap the blades of the hole saw, and drill half way through from each side. The outside curve of the wing is cut with a well soaped jeweler's saw. The connecting bar is cut (well within the lines since we're just roughing-out here) with repeated cuts of a thin bladed knife.
Once the ffs are roughed-in, finger planes are used to shape the arch around the ffs. In this way, the arch can be styled to fit the ff placement and make the ffs sit parallel to the edge of the plate when viewed from the side. The lower wing is pushed up from the inside of the plate when using the plane to help accomplish this. The graduations were left thick to account for this.
insert illustration of scooping around the ffs here
The illustration above shows the scooping done with a finger plane to get the ff to sit flat on the arch (parallel to the edge of the plate). It also shows a slight peak in the topography of the plate just above the superior edge of the lower lobe. This results from the use of the plane around the opening of the lobe, and is present on Guarneri's instruments. It also shows a very slight dip just above the upper lobe. This results from the use of a scraper in the final scraping of the top. TMB accomplishes this by placing a finger tip over the opening of the lobe and scraping away from the finger tip. Again this is seen on old instruments when viewed laterally with a straight edge placed longitudinally over the area.
When scraping away the tool marks left by the finger plane, don't be too careful to feather this area in to the rest of the arch. The slight longitudinal furrows left by the plane make a nice depression in which varnish is trapped, and as above, are seen in Guarneri's work as well.
Once the arching has progressed to this point further refinement of the graduations can take place. Before beginning the ffs, the top was rough graduated to 5.5-6mm. Now that the ffs are rough cut and the scooping/arching around them is completed, the graduations around the ffs can be brought down to 4mm. With the plate at this thickness, refining cuts to the ff profiles can be made.
The distance between the ffs is critical. Wherever possible, make adjustments to the size and appearance of the ffs to the lateral (distal) margins of the connecting bars. Generally the treble side ff is opened more than the bass, to allow for soundpost placement. The notches are marked by dividing the distance between the apical ends of the wings in half and marking an arc from the upper wing tip with a compass.