Building Babbage: An Open-Access, 3D-Printed Difference Engine No. 2 Kit

Abstract

Difference Engine No. 2, designed by Charles Babbage between 1847 and 1849, is a mechanical calculator capable of tabulating seventh-order polynomials to thirty-one decimal places. Construction of the Engine, which was never built during Babbage's lifetime, was fully completed by the London Science Museum in 2002, proving the viability of his intricate design based on the method of finite differences. This project presents an open-access, 3D-printed kit of Difference Engine No. 2's Calculation Section, scaled to a computational limit of third-order polynomials to four digits. The kit measures roughly two feet long, nine inches tall, and nine and a half inches wide, sitting at a scale sufficiently small for a hobbyist 3D-printer but sufficiently large to visualize the complete mechanisms of the Calculation Section. Challenges included a lack of dimensions and manufacturing detail in the original drawings, and adaptation to the tolerance and friction limitations of 3D-printing. Assembly of the final kit requires no tools beyond super glue and pliers, and all components are 3D-printed with the exception of the springs from twelve Pilot G-2 Gel pens. The CAD and 3D-print files, as well as assembly documentation, have been made publicly available on MakerWorld, providing an entry point for educators and enthusiasts alike to gain hands-on experience with early mechanical computing.