The thumb when extended is adjustable in one of three positions by moving the upper pin.
The thumb stows by moving the upper pin.
The thumb was designed starting with a scaled photo of the excavator bucket and stick. The photo was scaled to actual size using the yardstick. The CAD drawing was animated at the bucket hinge point to simulate the bucket and stick and avoid interference over their range of motion. The actual thumb was then designed to fit the adapted CAD drawing of the bucket and stick.
The rectangular cross web pieces have tabs that fit to about 2/3 depth in the corresponding slots. The tabs are then plug-welded creating no-distortion welds whose tops are approximately flush with the adjacent surface. This is a great fabrication style, offering self-alignment of the parts, nearly no distortion during the welding process, and strong, fast welds.
