Simultaneity (SIM) vs. Separation (SEP) Requirements

SIM vs. SEP: When to Use Each

SIM (Simultaneous)
Apply when features share the same datum system and must be checked together in one setup.
Example: Two shaft‑end features that mate with a timing gear and a cam simultaneously.

SEP (Separate)
Apply when features share the same datum system but can be inspected individually, without simultaneous alignment.
Example: Two pulley‑mount features at opposite ends of a shaft, checked separately.

Key Points: Simultaneity vs. Separation

1.Different Datum Systems → No simultaneity requirement applies.
(Different datums, datum order, or entity states.)

2.Unconstrained Parts → Compare SIM vs. SEP effects during analysis.

3.Fixture‑Based Inspection → SIM is applied by default (fully constrained).

4.Standard‑Based Defaults

1.ASME → SIM by default.

2.ISO → SEP by default (use “CZ” or “CZR” suffix to apply SIM).

5.Datum Shift

1.SIM → All features in same datum system share the same datum shift.

2.SEP → Features may be simulated under different datum shift states.

6.Composite Tolerances → SIM does not apply to the lower frame (feature‑to‑feature control).

DTAS 3D: SIM vs SEP – Setup & Verification

1.Select ASME tolerance standard in DTAS 3D.

2.Create features: two plane features and two hole‑group features.

3.Hole‑Pin Group: Shares the same datum system, zero tolerance → apply SIM (simultaneity) principle.

4.Hole Group: Shares the same datum system, zero tolerance → apply SEP (separation) principle.

5.Establish measurements:

1.For hole group → SEP principle.

2.For hole‑pin group → SIM principle.

The setup visually and numerically validates how SIM and SEP affect variation and alignment in a shared datum context.

DTAS 3D: SIM vs SEP – Summary

1. DTAS 3D follows strict GD&T standards, enabling tolerance simulation under SIM (simultaneous) and SEP (separate) requirements.

2. 2.The software adapts to diverse customer tolerance needs, delivering more accurate and reliable simulation results.

3. 3.SIM and SEP principles apply to both under‑constrained and fully constrained part states, ensuring realistic fixture‑based and free‑variation analysis.

   
   

Software Demo