A wood planing machine includes a carriage having four corners mounted on a base via four hollow posts. Four screw rods are disposed rotatably in the posts. Four tubular threaded members are secured to the corners of the carriage, and are disposed within the posts, respectively. Each of the threaded members defines a threaded bore for engaging the respective screw rod, and has an internally threaded portion, and a circumferential slot formed through the internally threaded portion to divide the same into upper and lower parts. The upper part has a bottom surface confining a top end of the slot. The lower part is formed with a threaded bore therethrough. A locking bolt engages the threaded bore in the lower part, and presses against the bottom surface of the upper part such that threads on the upper parts press upwardly against the screw rods and that threads on the lower parts press downwardly against the screw rods.