GD&T Project – Overview

To understand and further familiarize ourselves with GD&T tolerating and call outs, we were tasked with revising the initial aluminum clock base drawing provided by the Mech-200 Clock Project. The goal is to identify critical features on the clock base necessary for function, then basing the call outs on those critical features.

The initial drawing is shown below (source: Mech-200A Lab Manual, Instructor James Tillotson)

Evaluating Key Functionality

To be considered a “successful clock base”, the clock must be able to:

– Sit flat and steady on a table without rocking

– Accommodate the hardware mounting the brass pencil holder and steel pen holder
> Counter sink/bore holes must be deep enough to ensure hardware doesn’t protrude

– Be able to fit in CNC machine fixture in order to create slot for acrylic piece
> Drilled through holes must be within given tolerance of +/- 0.005″ bilaterally

Based on these key functionality features, Datums were selected accordingly based on functionality and usefulness for the manufacturing/metrology processes.

Updated Technical Drawing (GD&T Practice)

The Datums A and B were chosen primarily due to the location tolerance of the through holes being so essential in functionality, especially in drilling the Clock face slot. The last datum, C, was chosen as flatness is a key feature in this part. A flatness call out on top and bottom ensures aesthetic functionality as well as prevents the base from rocking back and forth. With additional engineering experience, I believe GD&T will become much easier in practice.