Abstract: A lumber trimmer comprises a saw table for transversely moving lumber pieces to be trimmed, a stationary cross-cut saw for cutting one end of the lumber pieces and a plurality of trim saws for cutting the other end. All saws are disposed along a line extending lengthwise with the trim saws mounted at regular intervals on a saw carriage which is displaceable in the lengthwise direction. A linear pneumatic positioner for the saw carriage comprises three double-acting cylinders connected with each other in series relation. The ratios of the lengths of stroke of the cylinders are 1 to 2 to 3, so that the positioner is capable of positioning the saw carriage at any selected one of seven uniformly spaced-apart positions.