A medical instrument includes a roll mechanism that rotates an instrument shaft. The roll mechanism may include a first gear coupled to the instrument shaft and meshed with a second gear. One of gears may be a spur gear while the other gear may be a beveloid gear. Further, the spur gear and the beveloid gear may be in a gear train containing a compressible gear, e.g., a gear with an inner center piece, an outer ring, and a flexible interconnecting structure between the inner center piece and the outer ring. With a compressible gear, an interference fit of in the gear train may be within manufacturing variations of the gear train, and the compressible gear may deflect radially away from the interference fit.
