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From: Ross
Remote Name: 76.101.10.136
Date: 19 Jun 2007
Time: 07:11:50 -0400
Luthier’s Weblog 6/19/07 Attack! Attack! The robot luthier decides to avoid the question of whether to design for lateral string excitation or vertical. Which is good because he is unsure how to do this, although he suspects the height of the x-brace at the crossing and the degree of taper of the brace members may be involved. Another mental bookmark for reflection. The difficulty with too specialized a design is that the instrument may fall into the wrong hands, or that execution may lag behind concept (a lot of that going around). With the X-brace a given, the builder now looks at his plantilla template and lays out the X on the underside of the top. He starts with the location of the bridge pins, realizing the brace must allow room for the pins and string ball ends to be unimpeded. Moving the crossing of the X far enough toward the neck to allow for this, he varies the angle of the crossing to divide the top into four sectors. His goal is to make the east and west and south sectors ( as viewed with the neck describing “North” position) roughly equal in area. He wishes to assure that no sector be dramatically stiffer than the others. This is more of a challenge with an asymmetric plantilla, but the robot luthier was good in Art, and has a reasonably accurate eye. Plus, close is probably good enough. The builder’s many critics may argue that the angle of incidence of the X-brace’s legs should be determined by the stiffness of the individual top plate used. He replies, in a rather saucy manner, that he would probably employ that method if he was unequal to the task of varying plate thickness to accomplish desired stiffness. With the top plate divided into segments by the X-brace, the bridge plate suggests itself. Bordered east and west by the X-brace members, it needs to extend north and south slightly more, say a quarter inch, than the bridge, which is located on the outside. Bridge plate material need be hard enough to resist the forces placed on it by the strings’ ball ends. Rosewood, maple or any other tough, hard, stable wood is suitable. Thickness , maybe a tenth of an inch. Grain orientation is important. The builder uses quarter sawn plate material with the grain neither perpendicular nor parallel to the instrument’s centerline, but rather dividing the difference and quartering SW/NE or NW/SE. This helps to avoid splitting along the line of bridge pin holes, a repair that the builder has needed to perform on many makes of guitars often in the past. Besides supporting the ball ends and the bridge in it’s struggle to avoid rolling forward with the pull of the strings, the bridge plate provides stiffness in the area most associated with the propagation of the higher frequencies. Ross Teigen 9:08 am