10.1 Composite Position Tolerancing

ASME GDTP Senior Level Exam

Track your progress as you read

Finished sections get a check mark.

1 Introduction & Exam Overview

1.1 Current Exam Facts 1.2 Senior Level vs Technologist and Y14.5 Revisions 1.3 How to Use This Guide and Study Strategy 1.4 The Y14.5-2018 Senior Exam and What Changed from 2009

2 Dimensioning and Symbology

2.1 Y14.5 Dimensioning Rules, Limits, and Fits 2.2 Basic Dimensions and Their Role 2.3 Feature Control Frame Structure and Reading 2.4 GD&T Symbols, Modifiers, and Communication 2.5 Screw Threads, Gears, and Splines 2.6 Angular Surfaces, Tapers, Radii, and Special Tolerance Cases

3 Datum Referencing I: Selection and Precedence

3.1 Functional Datum Feature Selection 3.2 Datum Precedence and Degrees of Freedom 3.3 Datum Targets 3.4 Datum Feature Simulators

4 Datum Referencing II: Modifiers and Shift

4.1 Multiple Datum Features and Datum Reference Frames 4.2 RMB, MMB, and LMB on Datum Features 4.3 Datum Shift Behavior 4.4 Planar vs Datum Feature of Size

5 Datum Referencing III: Setup and Calculations

5.1 Inclined and Translated Datum Features 5.2 Inspection Setup and Datum Establishment 5.3 Datum Calculation Walkthrough 5.4 Customized Datum Reference Frames and Rotational Constraint 5.5 Free State, Restrained Condition, and Nonrigid Parts

6 Form Controls

6.1 Flatness and Straightness 6.2 Circularity and Cylindricity 6.3 Rule #1, Form, and Size

7 Orientation Controls

7.1 Parallelism, Perpendicularity, and Angularity 7.2 Orientation Zones and Material Modifiers 7.3 Avoiding Unnecessary Orientation and Over-Control

8 Location I: Position and Boundaries

8.1 Position Tolerancing and True Position 8.2 Virtual and Resultant Condition 8.3 Bonus Tolerance at MMC and LMC

9 Location II: Application and Modifiers

9.1 Selecting MMC, LMC, and RFS by Function 9.2 Fixed and Floating Fastener Formulas 9.3 Projected Tolerance Zones 9.4 Coordinate Conversion and Appendix B Position Calculations

10 Location III: Patterns and Allocation

10.1 Composite Position Tolerancing 10.2 Patterns, Simultaneous Requirements, and Multiple Segments 10.3 Slots, Tabs, and Tolerance Allocation 10.4 Coaxial Feature Controls, Concentricity, and Symmetry

11 Profile I: Fundamentals and Strategy

11.1 Profile of Line and Surface 11.2 Defining the True Profile 11.3 Datum-Referenced Profile Strategy 11.4 Equal and Unequal Disposition

12 Profile II: Scope and Verification

12.1 All-Around, All-Over, and Limited Scope 12.2 Composite Profile and Coplanarity 12.3 Castings, Weldments, Sheet Metal, and CMM Evaluation 12.4 Combined Controls and Profile as a Refinement

13 Runout Controls

13.1 Circular and Total Runout 13.2 Datum-Axis Simulation and Rotating Parts 13.3 Runout vs Position, Profile, and Form

14 Exam Strategy and Calculations

14.1 Virtual/Resultant Condition and Bonus Formulas 14.2 Datum Shift and Worst-Case Boundary Calculations 14.3 Functional Gaging and Verification 14.4 Test-Day Tactics, Common Traps, and Review

10.1 Composite Position Tolerancing

Key Takeaways Explain This Topic AI

A composite position feature control frame has one position symbol and two or more segments: the upper Pattern Locating Tolerance Zone Framework (PLTZF) locates the pattern to the datums, and the lower Feature Relating Tolerance Zone Framework (FRTZF) refines feature-to-feature within the pattern.

The lower (FRTZF) segment may drop datum references that locate the pattern; it can repeat only the datums needed to orient or refine the pattern, and it never repeats a datum reference that locates the pattern to the part.

Datum references in each segment are read in order and with their modifiers; if the lower segment drops the locating datum, the pattern is free to translate as a group relative to that datum, while feature-to-feature spacing and orientation remain controlled.

A 4-hole pattern with upper Ø0.5 to A|B|C and lower Ø0.1 to A|B means each hole's axis must lie within Ø0.1 of its true position within the pattern (FRTZF), while the pattern as a group must lie within Ø0.5 of datums A, B, C (PLTZF).

The most common Senior trap is treating the lower segment as a tighter location to all datums; the lower segment is a refinement of the pattern internally, not a stricter location of the pattern to the part.

Last updated: August 2026

10.1 Composite Position Tolerancing

Quick Answer: A composite position control is one position symbol with two or more segments. The upper segment is the Pattern Locating Tolerance Zone Framework (PLTZF) — it locates the whole pattern to the datums. The lower segment is the Feature Relating Tolerance Zone Framework (FRTZF) — it refines feature-to-feature within the pattern. The lower segment may drop a locating datum; it never re-locates the pattern to the part.

Why two levels are needed

A pattern of holes has two independent geometric concerns: (1) where the pattern as a group sits on the part (location to the datums), and (2) how accurately the holes are spaced relative to each other within the pattern. Functionally these are different — a bolt circle may need to be located to the part within ±0.25, while the holes within the circle must be spaced to each other within ±0.05 so all four bolts engage a mating cover. A single position tolerance cannot separate these; either it is loose enough for location (and the holes can drift within the pattern) or tight enough for spacing (and the pattern is over-controlled to the part). Composite position separates them into two segments of one control.

Anatomy of the feature control frame | ⊕ | Ø0.5 | A | B | C |
| | Ø0.1 | A | B | |

One position symbol (⊕) governs both rows — this is what makes it composite. The upper row is the PLTZF : Ø0.5 to A|B|C, locating the pattern. The lower row is the FRTZF : Ø0.1 to A|B, refining the pattern internally. The lower segment carries a smaller tolerance, and it may reference fewer datums.

Rules for which datums carry into each segment

The upper (PLTZF) segment must reference all datums needed to locate the pattern — typically the primary, secondary, and tertiary datums (A|B|C).

The lower (FRTZF) segment may drop one or more datums , but the datums it does reference must appear in the same order as in the upper segment. You cannot reorder or introduce new datums in the lower segment.

A datum dropped from the lower segment means the pattern is free to translate (and in some cases rotate, if a datum constraining rotation is dropped) as a group relative to that datum — but the feature-to-feature relationship within the pattern stays at the tighter FRTZF value.

If a datum is repeated in the lower segment, it constrains only what that datum controls at that level — typically orientation, not location. For example, repeating A (a planar primary datum) in the FRTZF keeps the pattern perpendicular to A but does not re-locate the pattern along B or C.

Worked example — 4-hole bolt circle
A flange has a 4-hole bolt circle of Ø80 with four Ø10 holes. The drawing specifies: | ⊕ | Ø0.5 | A | B | C |
| | Ø0.1 | A | B | |

Where A is the flange face, B is the Ø40 central bore, and C is a radial datum notch.

PLTZF (upper, Ø0.5 to A|B|C): the four true positions of the holes form a perfect Ø80 bolt circle located to A, B, and C. Each hole's axis must lie within a Ø0.5 cylinder centered on its true position. This controls where the bolt circle sits on the flange — its height relative to A, concentricity to B, and angular position relative to C.

FRTZF (lower, Ø0.1 to A|B): the four holes must also lie within Ø0.1 of their true positions relative to each other , with the pattern oriented to A (perpendicularity) and B (clocking). Because C is dropped, the pattern may rotate as a group around B by up to the PLTZF allowance, but the four holes stay spaced to Ø0.1 internally.

Verification: the CMM first checks the pattern's location to A|B|C against Ø0.5 (PLTZF). Then it checks each hole against its true position within the pattern at Ø0.1 (FRTZF), using only A and B for orientation. The lower check is not a stricter location of the pattern to C; it is a refinement of the holes to each other.

Reading-decision table — which datum controls what

Datum In PLTZF (upper)? In FRTZF (lower)? What it controls at each level

A (flange face) Yes Yes (repeated) Upper: pattern height + perpendicularity. Lower: perpendicularity only — pattern stays normal to A but is free to float along the surface

B (central bore) Yes Yes (repeated) Upper: pattern concentric to B. Lower: pattern clocked to B but free to translate radially within the upper zone

C (radial notch) Yes No (dropped) Upper: angular position of the pattern around B. Lower: nothing — pattern may rotate as a group within the PLTZF allowance

Reading a segment from the frame

To read any composite position frame:

Confirm one position symbol governs both segments. If each segment has its own position symbol, it is not composite — it is two single-segment controls (see §10.2).

Read the upper segment as the pattern's location tolerance to the full datum reference frame.

Read the lower segment as a refinement of the pattern internally, with only the datums shown (same order as upper, possibly fewer).

Note any datum modifiers (MMC, LMC, RFS implied) — they must be considered per segment. A modifier on a datum in the upper segment does not automatically apply to the lower; the lower segment's datum references are read independently for modifiers shown there.

Senior-level traps

Treating the FRTZF as a stricter location to all datums. The lower segment refines the pattern internally; if it drops C, the pattern is free to rotate as a group relative to C. A candidate who applies Ø0.1 to all three datums is over-constraining the part and rejecting good hardware.

Adding a new datum in the lower segment. The FRTZF may only use a subset of the upper segment's datums. Introducing a new datum is not permitted in a composite frame.

Forgetting that the lower segment's tolerance is a refinement, not a replacement. A feature must satisfy both segments simultaneously — the lower segment adds a tighter internal constraint, it does not relax the upper one.

Misreading multiple single-segment frames as composite. Two separate single-segment position frames (each with its own symbol) are independent controls, not a PLTZF/FRTZF pair. The composite frame is identified by the single position symbol shared across segments.