In Stanford's introductory CNC machining class the first project assigned to all students is to create a bottle opener capable of popping off crimped crown caps and unscrewing twist-off caps. Almost all students in this course create a simple, 2.5D, single piece tool with varying degrees of utility and aesthetic appeal. I chose to indulge my desire to create something more mechanical as a reflection of my personality and interests.

I decided to build a guitar capo, a device which is used to clamp the strings against the fretboard to increase the pitch of the "open position" by reducing the overall string length. The clamp would be capable of holding the cap tight enough to twist off a cap and a traditional lever-style bottle opener would be built into one of the hand grips.

The majority of capos being marketed today are based around clamping mechanisms using either a torsional spring, an overcenter clamp, or a locking cam. In order to give my design a more unique functionality and a distinct "mechanically engineered" appearance I decided to use an exposed linear spring to drive a simple linkage. As the handles are squeezed the slider rolls on the spherical bearing attached to the push rod and the spring is compressed. Once in position the clamp is released around the guitar neck.

This design, in addition to its obvious visual and functional statement, incorporated a few subtle details to address some common problems with modern capo designs. Many capos apply excessive pressure on the strings which pulls the guitar out of tune. By allowing the spring length to be finely adjusted with a thumbwheel, clamping pressure issues are eliminated. The small cutout in the rubber face allows clearance for the lowest string to be unclamped if desired, a configuration that most capos on the market do not usually accommodate.