Research and Design of a 3D Printed Torque Wrench

Abstract

Additive manufacturing (AM) has developed from rapid prototyping technology into a versatile production method capable of delivering functional, customised tools. In parallel, the growing use of lightweight bicycle components with specified tightening torques has created a niche for low-cost torque tools that can be adapted to specific geometries and are accessible to casual users. The aim of this thesis was to investigate the feasibility of a 3D-printed torque-limiting wrench produced by fused deposition modelling (FDM), and to evaluate which wrench concept and geometry are most suitable with respect to achievable torque accuracy, repeatability and manufacturability using consumer-grade materials and printers. A target torque accuracy of ±25% of the nominal value was set as a reference for the assessment. The study began with a literature review on additive manufacturing processes, design for additive manufacturing (DfAM), FDM process parameters and materials, as well as existing examples of additively manufactured tooling and slipping mechanisms. During the thesis process, two concepts were developed and evaluated. Concept 1 adopted an analytical methodology approach and relied on a friction-based slipping mechanism consisting of a bladed rotor and surrounding casing. The coefficient of static friction for extruded PLA on PLA was obtained experimentally using an inclined plane, and a calculation model was developed to relate blade geometry, normal force and frictional force to the desired slipping moment. A parametric FEM simulation in Ansys was used to predict how blade height, thickness, and fillet radius impact reaction force, after which selected configurations were printed and tested. Although slipping could be achieved, the measured values deviated substantially from theoretical predictions and lacked repeatability, leading to the conclusion that a purely friction-driven approach was not suitable for a practical use. The second concept implemented an experimental and iterative approach to improve upon the limitations of the friction-based design. Concept 2 employed a ratcheting mechanism in which a compliant pin embedded in the case interacts with a wave-shaped inner drive gear to create a distinct torquing action. The design was developed through four successive iterations, with changes focused on clearance, gear retention, pin geometry, and overall usability. This refinement enabled the ratcheting concept to be manufactured as a self-supporting, consolidated assembly that remained functional without additional operations. Overall, the thesis showed that 3D-printed polymer tools can serve as application-specific, low-cost indicators of tightening level in varying applications, and it proposes design and process guidelines for engineers and hobbyists interested in using additive manufacturing for functional torque tools and similar compliant mechanisms.