Composite VS Single Segment - Question...

[[Ja...]]

Can someone explain composite and single segment position callouts to me plainly? My understanding is with composite, the top segment defines the individual features, to the specified datums, whereas the bottom segment defines the collective features (as a pattern) to the specified datums.

With single segment, both the top and bottom segments are defining the individual features (not collective or pattern) to the specifed datums.

Is this correct?

Edited May 1

[[Ma...]]

From my understanding - when you have fully defined datums, then there is no difference in result between single and sim.

If you have not defined fully, then in single you do each feature alone, so you will have differences in translation/rotation for each feature TP.

For sim it's behaving like pattern - you will have only one translation/rotation for all features.

 

I hope someone will correct me, if i am wrong

[[Je...]]

Please sign in to view this username.

Great question, Jake. Important to keep in mind:

Composite Position Tolerancing at first glance looks a lot like multiple single-segment tolerancing. The visual differentiator is whether there is only one control symbol that spans down to reference multiple segments (composite), or if multiple control symbols exist, one for each segment (multiple single-segment frames).

 

Composite Position Tolerancing
========================
A composite feature control frame uses stacked segments beneath a single geometric control symbol.

The top segment (official term is "PLTZF" – Pattern Locating Tolerance Zone Framework) controls the location and orientation of the entire pattern relative to the datum reference frame [ASME Y14.5-2009, §7.4.1.1, Fig. 7-29].

The bottom segment (official term is "FRTZF" – Feature Relating Tolerance Zone Framework) controls orientation and feature-to-feature relationships within the pattern, but not location to the datums [§7.4.1.2].

This allows the lower segment to refine the pattern internally while the entire pattern “floats” within the larger zone defined by the top segment.

Datums in the lower segment must match the top segment in order and modifiers, or be omitted entirely if only used for orientation [§7.4.1.3].

Multiple Single Segment Position Tolerancing
==================================
This method uses two separate feature control frames, each a full single-segment callout with its own control symbol.

Each frame fully controls location and orientation to the specified datums, typically with different tolerance values [§7.4.8, Fig. 7-37].

Unlike composite, there is no internal pattern refinement—each frame re-establishes full datum control.

To avoid triggering the Simultaneous Requirement rule, one or more datum references must differ between the frames (e.g., omitting the tertiary datum in the second frame) [§4.17, §7.4.4].
 

Quick Analogy
===========
Composite = One guiding system for the whole pattern and the spacing within it—like a train with cars connected, moving within a shared corridor. 🚂🚃🚋🚃🚋

Multiple Single Segment = Two separate trains, each independently controlled, though traveling over similar tracks.     🚂🚃🚋🚃🚋      🚂🚃🚋🚃🚋
 

Edited May 1

[[To...]]

This guy has a great video series on GD&T, especially on the composite vs. multi-segment topic.  Below is a link to a playlist of his videos.