Date of Award

5-4-2026

Degree Type

Capstone Project

First Advisor

Professor Bahram Nassersharif

Abstract

This project documents our year-long design and development of the Adjustable Linear Ratchet Wrench, an original mechanical consumer product developed for the Mechanical Engineering Capstone Design course. The goal of the project was to create a new mechanical device that addresses a common user need, has broad consumer appeal, can be produced within a realistic retail price range, and relies on core mechanical engineering principles. After evaluating multiple early invention ideas, our team narrowed the project scope to hand tools and selected the adjustable wrench as the product area because conventional adjustable wrenches are common, mechanically simple, and still limited by slow manual adjustment and awkward operation in confined spaces.

Our final concept uses a linear, bidirectional ratcheting mechanism inspired by the operation of a socket wrench but implemented through linear jaw motion instead of rotation. The mechanism uses a rack, a redesigned three-tooth pawl, springs, and a cam to control directional engagement. The cam allows the pawl engagement state to change so the jaw can move smoothly in one direction while resisting motion in the opposite direction. This layout was developed through concept generation, Pugh analysis, QFD evaluation, CAD modeling, additive manufacturing, physical testing, and SolidWorks stress analysis.

The final prototype demonstrated the required operating behavior. The wrench achieved an adjustment range exceeding the original 6-24 mm requirement, with measured motion from approximately 0 mm to greater than 24 mm. The mechanism also met the adjustment time requirement, averaging 1.34 seconds compared with a target of 2.5 seconds or less. Mechanism performance was evaluated by cycling the jaw through both directions of ratcheting across the adjustment range, and the final version operated smoothly and consistently. The pawl was treated as the critical load-bearing component because it is the first part expected to fail under load. A SolidWorks static stress simulation of the redesigned pawl under a 1000 N load produced a maximum von Mises stress of 1.432 x 10^8 Pa, or 143.2 MPa, compared with a listed yield strength of 1.700 x 10^8 Pa, or 170 MPa. This gives an approximate static factor of safety of 1.19.

Overall, the project successfully demonstrated a functional adjustable wrench concept with a novel linear bidirectional ratcheting mechanism. The design met the main functional targets established by the team, while also identifying the pawl tooth roots and base transition as the most important areas for future strength improvement.

Comments

Team Name: Team 19

Sponsor: Professor Bahram Nassersharif

Document Reference: URI-MCE-2026-FDR-019

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