The Problem: Wasting Money on Unnecessary Precision
One of the most common mistakes we see is a customer spending too much on precision where it’s not needed. This often leads to overpriced parts and inefficiencies.
The issue? Too much focus on the external dimensions of a part, rather than how internal components fit and function together.
See the below part for example. The keyed feature (the bored out circle with the key cut out on the right) has a true position to the outside. That is, it’s measured from the outside of the entire part. The bore in this example would default to the block tolerances which are most likely much bigger. The part could be made to print and be within tolerance, but the shaft & key wouldn’t fit!
The Solution: Internal Alignment Over External Appearance
The smarter approach is to prioritize the internal relationships of parts. Think of a gearbox: it’s more important that the gears inside align well with each other than with the gearbox casing.
It is more important that the keyed feature is true to the bore than the outside. That’s the relationship that actually matters. Plus, the part would be cheaper if the true position had referenced the bore.
The preference for true position between features streamlines the manufacturing processes. By focusing on internal relationships, designers can avoid overly stringent tolerances on external dimensions, reducing the likelihood of rejects and simplifying production workflows. This method optimizes efficiency and minimizes costs, as it enables a more targeted approach to geometric dimensioning and tolerancing.
How to Think This Way
When defining true position between features, designers should consider the internal relationships, ensuring a more accurate and functional alignment within an assembly.
This approach is especially crucial in complex designs, where the interplay of internal components significantly impacts overall performance. It also reduces manufacturing costs.
Summary
Prioritizing true position between features enhances precision, functionality, and manufacturing efficiency, making it a preferred choice for meticulous and effective design and production practices.
In other words, using true position to locate features in relation to the outside is driving up your costs.
