Robotic surgical tool with replaceable carriage

A method of assembling a robotic surgical tool includes providing a handle having first and second ends, a lead screw, and a spline extendable between the first and second ends. The lead screw is rotated in a first direction to translate an elevator layer of a carriage proximally along a longitudinal axis of the handle, the elevator layer being movably mounted to the lead screw at a carriage nut. One or more additional layers of the carriage are removably coupled to the elevator layer and an elongate shaft extends distally from the additional layers, and an end effector is arranged at a distal end of the shaft. The elevator layer is penetrated by the end effector and the shaft upon coupling the additional layers to the elevator layer, and the lead screw is rotated in a second direction opposite the first direction to translate the carriage distally.