GD&T and Drawing Creation Skill

Purpose

The GD&T and Drawing Creation skill provides specialized capabilities for geometric dimensioning and tolerancing specification per ASME Y14.5 and ISO 1101, enabling proper documentation of design intent for manufacturing.

Capabilities

• ASME Y14.5-2018 interpretation and application
• Datum feature selection and reference frame establishment
• Geometric tolerance specification and symbol usage
• Tolerance stack-up analysis (worst-case and statistical)
• Drawing view creation and annotation
• Bill of materials generation
• Revision control and ECO documentation
• Drawing checker automation

Usage Guidelines

Datum Reference Frame

Datum Selection Principles

1. Primary Datum (A)

   • Establishes orientation
   • Contacts 3 points minimum
   • Usually largest/most stable surface

2. Secondary Datum (B)

   • Establishes rotation lock
   • Contacts 2 points minimum
   • Perpendicular to primary

3. Tertiary Datum (C)

   • Establishes location
   • Contacts 1 point minimum
   • Completes coordinate system

Datum Feature Selection

Function	Recommended Datum Features
Mounting surface	Primary: Mounting face
Shaft alignment	Primary: Axis (A-B pattern)
Hole pattern	Secondary/Tertiary: Pattern center
Symmetric part	Primary: Plane of symmetry

Geometric Tolerances

Form Controls

Symbol	Control	Datum Required
Straightness	Line element deviation	No
Flatness	Surface deviation	No
Circularity	Cross-section deviation	No
Cylindricity	Combined circularity + straightness	No

Orientation Controls

Symbol	Control	Datum Required
Perpendicularity	90 degrees to datum	Yes
Parallelism	Parallel to datum	Yes
Angularity	Specified angle to datum	Yes

Location Controls

Symbol	Control	Datum Required
Position	True position from datums	Yes
Concentricity	Axis coincidence	Yes
Symmetry	Median plane coincidence	Yes

Runout Controls

Symbol	Control	Datum Required
Circular runout	Single revolution check	Yes (axis)
Total runout	Full surface check	Yes (axis)

Profile Controls

Symbol	Control	Datum Required
Profile of a line	2D outline control	Optional
Profile of a surface	3D surface control	Optional

Tolerance Specification

Position Tolerance Formula

Position tolerance = 2 * sqrt((dx)^2 + (dy)^2)

Where:
dx = deviation in X from true position
dy = deviation in Y from true position

MMC/LMC Modifiers

Modifier	Effect	Application
MMC (M)	Bonus tolerance as size departs	Assembly clearance
LMC (L)	Bonus at LMC	Wall thickness control
RFS	No bonus	Default per Y14.5-2018

Tolerance Zone Shapes

Cylindrical: Position of holes (diameter symbol)
Rectangular: Position of slots
Spherical: Ball location (S diameter symbol)

Drawing Creation

View Selection

1. Standard Views

   • Front view: Most descriptive
   • Top/side views: As needed
   • Isometric: For orientation

2. Section Views

   • Full section: Internal features
   • Half section: Symmetric parts
   • Broken-out: Local detail

3. Detail Views

   • Small features requiring enlargement
   • Complex tolerancing areas

Annotation Standards

1. Dimension Placement

   • Dimension in most descriptive view
   • Group related dimensions
   • Avoid crossing dimension lines
   • Reference features, not edges

2. Notes

   • General notes for common requirements
   • Local notes for specific features
   • Material and finish callouts

Process Integration

• ME-004: GD&T Specification and Drawing Creation

Input Schema

{
  "part_model": "CAD file reference",
  "functional_requirements": {
    "assembly_interfaces": "array",
    "critical_features": "array",
    "fit_requirements": "clearance|transition|interference"
  },
  "manufacturing_method": "machined|cast|molded|sheet_metal",
  "inspection_method": "CMM|optical|manual",
  "standard": "ASME_Y14.5|ISO_1101"
}

Output Schema

{
  "drawing_info": {
    "drawing_number": "string",
    "revision": "string",
    "sheet_count": "number"
  },
  "datum_reference_frame": {
    "primary": "string",
    "secondary": "string",
    "tertiary": "string"
  },
  "geometric_tolerances": [
    {
      "feature": "string",
      "tolerance_type": "string",
      "value": "number (mm)",
      "datums": "string",
      "modifiers": "string"
    }
  ],
  "critical_dimensions": "array",
  "bom": "array of components"
}

Best Practices

1. Select datums that reflect assembly function
2. Apply tolerances based on functional requirements
3. Use MMC where assembly fit is primary concern
4. Document datum feature simulators
5. Verify tolerance stack-ups for critical fits
6. Include inspection notes for complex features

Integration Points

• Connects with CAD Modeling for geometry
• Feeds into Tolerance Stack-Up for analysis
• Supports FAI Inspection for verification
• Integrates with Manufacturing for process capability