Dimensioning and Notes

​Why Are They Important?

They provide the complete information manufacturers need to bring the designer's vision to life and ensure proper fit, function, and compliance with specifications.

Precise measurements (length, width, height, diameters, tolerances) for accuracy.

​

​Dimensions

Additional instructions such as:

• Material specifications

• Surface finishes

• Assembly instructions

• References to industry standards

​Shop Notes

​Other Critical Information

• Tolerances for allowable variations.

• Multiple views for clarity (e.g., top, front, side, or sectional).

• Standard symbols for machining, threads, welds, etc.

Answer:

Dimensions and shop notes are needed if an object is to be manufactured according to the designer's specifications, ensuring accuracy and functionality.

• Dimensions: Define the sizes of the geometrical features of an object.

• Notes: Provide additional information not conveyed through dimensions.

​Purpose of Dimensions and Notes

Answer:

the sizes of the geometrical features of an object

Answer:

additional information not included in the dimensions.

• Unidirectional Dimensions:

  • Placed to read from the bottom of the drawing.

• Aligned Dimensions:

  • Placed parallel to the dimension line.

  • Numerals are read from:

    • The bottom of the drawing.

    • The right side of the drawing.

​How Dimensions are Placed

​How Dimensions are Placed

Notes and Leaders

• All dimensions shown with leaders and notes are lettered parallel to the bottom of the drawing, regardless of the dimensioning method used.

Answer:

the bottom of the drawing.

Answer:

the bottom and right side of the drawing.

• Dimension Lines:

  • Fine solid lines indicating distance and location.

  • Broken for insertion of dimensions.

  • Capped with arrowheads for clarity.

​Key Elements of Dimensioning

• Extension Lines:

  • Extend out from the drawing without touching it.

  • Project 1/8 in. (3.0 mm) beyond the last dimension line.

​Key Elements of Dimensioning

• Dimension Placement

  • Smaller or Detail Dimensions: Placed nearest the view.

  • Larger or Overall Dimensions: Placed farthest from the view.

​Key Elements of Dimensioning

• Placement: Place dimensions on views showing the true shape of the object.

• Avoid Crowding: Avoid placing dimensions within views unless necessary.

• Grouping: Group dimensions together; avoid scattering across the drawing.

• Completeness: Ensure all dimensions are complete to eliminate the need for scaling.

​Key Rules for Clarity and Accuracy

• Direction: Draw dimension lines parallel to measurement, staggering numerals for readability.

• No Duplication: Avoid duplicating or including unnecessary dimensions.

• Avoid Crossings: Plan to prevent dimension lines from crossing extension lines.

​Key Rules for Clarity and Accuracy

• Units:

  • Inches: Omit the inch symbol (") when all dimensions are in inches.

  • Metric: Use millimeters unless noted otherwise.

• Numerals: Write numerals and fractions with proper proportionality and alignment.

​Key Rules for Clarity and Accuracy

Answer:

Dimensions should be grouped together rather than scattered about the drawing.

Answer:

When all dimensions are in inches, the inch symbol (") is not used.

• Circles and Holes:

  • Use the Greek letter φ (phi) to indicate a diameter, placed before the dimension.

  • If unclear that a hole goes through, add THRU after the dimension.

  • Specify hole depth and features like spotfacing, counterboring, or countersinking with symbols.

​Key Guidelines for Dimensioning

• Arcs:

  • Dimension by specifying the radius (R), with "R" placed before the dimension.

• Concentric Circles:

  • Dimension diameters on the front view for clarity.

​Key Guidelines for Dimensioning

• Leader Lines:

  • Always point to the center of the diameter or arc.

• Cylindrical Parts:

  • Dimension from the centers, not the edges.

​Key Guidelines for Dimensioning

• Series of Holes:

  • Use a note to indicate:

    • Number of holes

    • Their size

    • The diameter of the circle on which they are located

​Key Guidelines for Dimensioning

Answer:

The circle diameter is indicated by the symbol φ. It is placed before the dimension.

• Angular dimensions are expressed in:

  • Degrees (°)

  • Minutes (')

  • Seconds (")

​Key Guidelines for Dimensioning

​Example - An angle might be dimensioned as 45° 30' 15", indicating:
45 degrees 30 minutes 15 seconds

• When the space between extension lines is too small for both numerals and arrowheads

  • Numerals are placed outside the extension lines.

  • Arrowheads point to the dimension lines from outside the space.

• Why This Matters

  This approach maintains clarity and ensures that dimensions remain legible, even in tight spaces, while adhering to drafting standards.

​Key Guidelines

• Metric Measurements: Widely used internationally to improve competitiveness.

• Transition Challenges:

  • Difficulty interfacing metric-designed parts with inch-standard parts at interfaces (joining surfaces).

• Collaboration: Industries working together must use the same measurement system to avoid inconsistencies.

​Key Insights

1. Dual Dimensioning: Includes both metric and conventional measurements.

2. Letters and Tabular Chart: Dimensions represented with reference letters tied to a chart.

3. Metric Dimensioning with Readout Chart: Metric dimensions supported by a chart for conventional equivalents.

4. Metric Units Only: Dimensions provided exclusively in metric units.

5. Undimensioned Master Drawings: Rely on undimensioned drawings as a reference, often used with digital models.

​Five Methods for Managing the Transition

1. A method of dimensioning engineering drawings with both inch and metric units.

2. Used to facilitate the transition between measurement systems.

3. Placement Rules

   • Inch Dimension First: For drawings produced in the United States.

   • Metric Dimension First: For drawings produced where metric is standard.

​What is Dual Dimensioning?

1. A technique where letters (A, B, C, etc.) replace inch or millimeter dimensions.

2. A tabular chart accompanies the drawing, listing the metric and inch equivalents for each letter.

3. Key Advantages

   • Simplifies the drawing by reducing clutter.

   • Allows for easy comparison of metric and inch dimensions.

​What is it?

1. Replace the dimensions on the drawing with corresponding letters.

2. Include a tabular chart with the drawing:

   • Matches each letter with its metric and inch equivalents.

​How it works

Answer:

Dual dimensioning is a method of presenting measurements on engineering drawings using both inch and metric units to accommodate different measurement systems. It is displayed using either the position method (one above the other) or the bracket method (dimensions in brackets).

Answer:

The person using the drawing gets the inch/millimeter sizes from the tabular chart included with the drawing.

• A method where parts are designed to metric standards with only metric dimensions on the drawing.

• A readout chart is added to show metric values and their inch equivalents.

• How it Works

  1. Metric Dimensions: Placed on the drawing.

  2. Readout Chart:

     • Left column: Metric dimensions.

     • Right column: Inch equivalents.

​What is it?

• A method of dimensioning where only metric units are used on the drawing.

Why Use It?

• Encourages engineers, designers, drafters, and craftworkers to "think metric."

• Simplifies the drawing by eliminating the need for conversions or dual measurements.

• Advantages

  • The quickest method to adopt metric standards.

  • Reduces confusion by focusing solely on one measurement system.

​What is it?

• Master Drawing: Created without dimensions.

• Customized Prints:

  • Metric dimensions added to one print.

  • Inch dimensions added to another.

  • Notes and details adapted for various languages (e.g., German, French, English, Japanese).

​What are Undimensioned Master Drawings?

• Allows flexibility for international production.

• Reduces clutter in the original master drawing.

• Key Considerations

  • Scales and Templates: Drafting personnel must have tools for both metric and conventional systems.

  • Metric Knowledge: A thorough understanding of the metric system is essential.

​Why Use This Method?

• Metric and inch systems are not always interchangeable:

  • No exact metric equivalent for some imperial sizes (e.g., 9/16 in. or 1.0 in.).

  • Custom machining may be required, increasing costs.

​Challenges

Answer:
A master drawing is a technical drawing created without dimensions. It serves as a base for creating multiple customized prints. Metric dimensions can be added to one print, inch dimensions to another, and notes can be tailored to different languages as needed for production. This approach allows flexibility for global collaboration and simplifies the adaptation of designs for various standards and languages.

• Standard Unit:

  • The millimeter (mm) is the standard unit for dimensioning engineering drawings.

• Decimal Format:

  • Use one-place decimals for most dimensions (e.g., 125.0).

  • Two or three decimal places are used for critical tolerances.

  • Full millimeter dimensions include a zero to the right of the decimal (e.g., 125.0).

​Key Rules

• Dimensions Less than 1 mm:

  • A zero must precede the decimal point (e.g., 0.5, not .5).

• Identification of Metric Drawings:

  • Include a note on the drawing:
    "All dimensions are in millimeters."

  • This eliminates the need to add "mm" after every dimension.

​Key Rules

• Spacing with Symbols:

  • A space must be placed between the dimension and the "mm" symbol:
    Correct: 125.0 mm
    Incorrect: 125.0mm

​Key Rules

• A precise system for specifying dimensions and tolerances on technical drawings.

• Ensures accuracy in form, profile, orientation, location, and runout of features.

• Standardized for global manufacturing and interchangeable parts.

​What is GD&T

• Geometric Characteristic Symbols:

  • Define tolerances for shape, position, and relationship of features.

• Datums:

  • Exact points, axes, planes, or surfaces used as references for locating features.

  • Identified by letters in boxes, attached to triangles or dimension lines.

​Key Features

• Feature Control Frame:

  • A rectangular box divided into compartments containing:

    • Characteristic symbols.

    • Allowable tolerance.

    • Datum reference letters.

  • Positioned alongside dimensions or extension lines.

​Key Features

• Provides an international standard for communication.

• Facilitates precision and economy in manufacturing.

• Ensures compatibility when parts are made in different locations.

​Why Use GD&T

Answer:
A highly precise system of specifying dimensions and tolerances on drawings is called Geometric Dimensioning and Tolerancing (GD&T).

Answer: datum

A datum is a reference feature used in geometric dimensioning and tolerancing (GD&T) to precisely locate and align other features of a part. It can be a point, axis, plane, or surface that serves as a starting point for measurements and defines the exact location or orientation of features in a consistent and repeatable way.

For example:

• A point datum might be used to locate the center of a circular feature.

• An axis datum could align cylindrical features.

• A plane datum might define a flat surface as a baseline for other measurements.

Datums are critical for ensuring consistency and accuracy in manufacturing, especially when parts are made in multiple locations or need to fit together perfectly with other components.