Violin Making Workbook
TMB likes grain lines on the bridge blank to be tight. They should line up across the horizon of the bridge, horizontal/parallel to the top of the instrument. Bridge blanks are dropped onto the granite flat plate to subjectively assess their tonal qualities. In deciding which side of the bridge to orient toward the fingerboard, examine the "flecks" in the wood. The inferior surface will be the side with the longer fleck distribution, or "tubes". Hence tubes=tailpiece; fleck=fingerboard.
Flatten the inferior aspect (tube side) on a flat plate with 180 grit sandpaper (enough to remove the trademark). The inferior aspect is slightly arched (like the superior aspect, but much less pronounced). This is effected by lifting the edges of the bridge off the sanding plate by one quarter to one half a millimeter. Follow up with 220 grit sandpaper, and then 320 grit.
Next, from the superior aspect ("fleck"/fingerboard side) the blank is thickness planed to 4.6 mm at the feet (the finished thickness after sanding will end up at 4.5 mm).
The feet are fit to the top of the instrument. Lick the feet to soften the wood and cut with a knife. Try frequently with a strong light behind to assess fit. Keep in mind that the inferior aspect of the bridge needs to be 90 degrees to the surface of the top. Keep checking the angle in an superior-inferior aspect as you cut the feet and lower the bridge further down on to the instrument. Terry likes to bring the bridge down as low as possible, without making the lateral aspects of the feet any narrower than 1.4 mm tall. As the fit gets closer, use a very soft (6B) pencil on the top of the instrument as transfer color. Keep the bridge between the taped marks, and move the bridge in an inferior-superior direction to mark the high spots with the transfer color.
Once the fit if the feet are established, hold the bridge in its proper place on the top, sight down the fingerboard from the nut, and mark the height of the FB on the bridge in pencil. Double check the pencil line by sighting down the FB. Now measure up from this line 4 mm on the E string side and 5.5 mm up on the G string side. Use a template to mark the arc across the bridge. Chisel down to this line. Lay out string placement on the top of the bridge, and file preliminary grooves. Set up tailpiece and nut with strings going over the bridge with just enough tension to hold things in place. Check string height at the inferior end of the FB. Adjust the height of the bridge accordingly.
The top third (supero-anterior aspect) of the bridge blank is slightly arched. This is accomplished by holding a block plane upside down and lightly passing the blank across the blade of the plane. There is a small amount of "overkill" in the cuts with the plane, which are blended with sandpaper on the flat plate by rocking and slightly lifting the edges of the blank as it is passed across the sandpaper. The arc is present in both the anterior-posterior and lateral planes, with the highest point just above the heart of the bridge. Finished thickness of the top of the blank is 1.25-1.35 mm with a very slight bevel sanded along each side with 320 grit paper. As with the back, sand with 180, 220 and 320 grit abrasive. The superior aspect needs to be name-stamped. TMB prefers small characters, and no blackening in the stamp indentation.
This is the point to carve out the machine marks on the inside of the heart and kidneys, and make any artistic enlargements in these areas. The sides are beveled slightly, the oblique cuts accentuated and the half circle lateral cuts enlarged. The bottom of the bridge (posterior) between the feet is arched to match the curve of the top of the instrument.
After sanding with 320 grit abrasive the bridge is ready to accept color. It is rubbed across a piece of short napped carpet the has been impregnated with powdered pigments (burnt umber, raw sienna, etc.) and then burnished with an ivory or bone burnisher. No additional sealer is used.
The bridge feet are fit to the top of the instrument using a very soft (6B) graphite pencil to provide transfer color. The feet are cut as low as possible at this point, however the height at the lateral terminus shouldn't be below 1.4mm.