Best practices for dimensioning parallelism from a datum

Hi Gregory,

When it comes to dimensioning parallelism, both methods—using basic dimensions with profile tolerances and a combination of ± tolerance with parallelism control—have their place, but here’s how I typically approach it:

Basic Dimensions with Profile Tolerances:
When to Use: Best for high-precision parts where you need tight control over form, orientation, and size in one go.
Why: Profile tolerances give you more comprehensive control, making sure everything aligns as it should without piling on separate tolerances for each feature.
Standards: I follow ASME Y14.5 for this, as it’s the gold standard in GD&T. It’s also aligned with ISO 1101 internationally.

± Tolerance with Parallelism Control:
When to Use: Ideal for simpler parts or when you’re mainly concerned with the size and basic alignment.
Why: It’s more straightforward and easier for teams familiar with traditional tolerancing methods. Plus, inspection can often be simpler with standard tools.
Standards: Still sticking with ASME Y14.5, but ISO 2768 is good if you’re working with general tolerances.

If precision is critical and you’re dealing with complex geometry, go with basic dimensions + profile tolerances. For simpler parts, ± tolerance with parallelism control should work fine and might save time and effort.

Hope this helps! Let me know if you need more details or have other questions!