In engineering, tolerance simulation is vital—and the choice of datum system directly shapes the outcome.

Different datums affect calculations, error analysis, and final designs, ultimately influencing product performance.

This article demonstrates how datum selection impacts simulation results, helping engineers apply tolerance simulation more effectively.

Using an ASME-based tolerance model in DTAS, we first show how different datums change the analysis of the same product.

Note 1: When the model uses a "face" as the primary reference, fit the faces together, and then install the pins; as shown in the figure below:

The assembly status is shown in the following figure:

Note 2: When using the "hole pin" as the primary reference point for the model, install the hole pin first, then fit the surfaces together; as shown in the diagram below:

The assembly status is shown in the following figure:

Summary
DTAS uses analytical modeling to clarify how datums function in tolerance standards.

Pin-hole assemblies are a common failure point in aerospace manufacturing, making positioning design vital for reliability. DTAS validates assembly schemes through tolerance modeling to improve product robustness, as shown below.

Case Study: Assembly Scheme 1 in DTAS

Objective
Measure coaxiality of gear centerlines at both ends to assess gear tilt under a defined assembly sequence and positioning scheme.

When designing gear and shaft assembly using a "surface" as the primary positioning datum, do not select "Whether to prioritize pin and bore". The assembly interface will look like the image below:

To add a uniform rotation state to the product, you can increase the angular tolerance and select "Arithmetic Sequence Distribution" in the distribution type box, as shown in the following figure:

The parameter settings have been modified, as shown in the image below:

The GD&T information for the part is shown in the following figure:

The coaxiality between gears is measured as shown in the figure below:

The measurement results are shown in the figure below:

Assembly Scheme 2
Objective:
Measure the coaxiality of gear centerlines at both product ends to evaluate gear tilt under the defined assembly sequence and positioning scheme.

When designing gear and shaft assembly with "pin" as the primary positioning datum, check "Whether to prioritize pin hole". The assembly interface is as follows:

To add a uniform rotation state to the product, you can increase the angular tolerance and select "Arithmetic Sequence Distribution" in the distribution type box, as shown in the following figure:

The parameter settings have been modified, as shown in the image below:

The GD&T information for the part is shown in the following figure:

The measurement results are shown in the figure below:

The video demonstration is as follows:

Summary

Two assembly control strategies—face‑dominant and pin‑dominant—significantly affect product coaxiality. DTAS clearly quantifies the impact of pin‑dominant positioning, providing actionable design‑optimization guidance.

Conclusion

In aerospace and beyond, tolerance simulation drives not only precision and efficiency, but also Industry 4.0 transformation. As technology advances, its role will expand—ensuring safer, higher‑quality outcomes across sectors.