Helical Crank

I walked across the oak landing and climbed the wooden rungs of a swivel chair onto the desktop. Near the edge, a heavy mechanical pencil sharpener was clamped to the wood. I approached its twin-rail mechanism. Two spring-loaded tabs formed an aperture at the front. With both hands, I pinched the chrome release levers together; the internal spring compressed smoothly, disengaging the clamp. I slid the faceplate forward along its polished guide rails until it locked at full extension. Stepping around to the rear, I gripped the wooden knob and turned the crank sixty degrees. Inside the cylindrical casing, the helical steel gears turned with a crisp, even click.