Design and fabrication of a pencil shoulder cutting device for a novel endcap

Abstract

The pencil shoulder cutting device is a stepper motor driven mechanism to cut a small groove into the end of a pencil, which is needed for a novel seed-capsule endcap for a new pencil called Sprout. The pencil was developed by a team of MIT graduate students, and the shoulder cutting device is one step in an automated assembly process for Sprout. The device autonomously cuts a 0.0075in. deep shoulder into one end of the pencil using a 0.25in. end mill. The device includes a stabilizing sleeve that reduces vibration of the pencil during machining, and creates a vacuum seal so that chips from the pencil are cleanly removed. The cutting time for each pencil is 2s, with an absolute accuracy of 3.1x10-4 in. for the depth of cut after ten tests with the machine. The capsules fit correctly onto the shoulders when done by hand, and the design will be confirmed once the entire machine is running autonomously.