a) a base plate;

b) an L-shaped sine plate with a pivot axis in the region of a juncture formed by a first laterally extending arm and a second vertically extending arm, said juncture defining a sharp corner height, said L-shaped sine plate having a smooth radiused surface on an outside of said juncture between said first arm and said second arm;

c) mounting means for supporting said L-shaped sine plate enabling said sine plate to pivot about said pivot axis, said mounting means including first and second side plates, each said side plate having at least one first opening facilitating attachment of said side plate to said base plate and at least one second opening for receiving a fastener which serves as an axle about which said sine bar pivots, wherein each said second opening in said first and second side plate is kidney shaped defining a smooth arc with a radius generally equal to a radius forming said smooth arcuate surface on said L-shaped arm;