Introduction
Drafting is a precise and structured form of technical drawing used in architecture, engineering, and design. One of the most fundamental aspects of drafting is the use of line weights (thicknesses) and line types (styles) to convey information clearly. Whether done by hand on a drafting board or digitally using CAD software, the correct use of lines ensures accuracy, readability, and proper communication of design intent.
This article explores the principles of line weights and line types, compares their application in manual (board) drafting versus computer-aided design (CAD), and examines best practices across different disciplines.
1. The Importance of Line Weights
Line weight refers to the thickness of a line on a drawing. Different weights create a visual hierarchy, helping drafters distinguish between primary and secondary elements.
Common Line Weights and Their Uses
| Line Weight | Purpose |
|---|---|
| Thick (0.7mm – 1.0mm) | Object outlines, section cuts, structural elements |
| Medium (0.35mm – 0.5mm) | Hidden lines, secondary features |
| Thin (0.18mm – 0.25mm) | Dimensions, text, centerlines, hatching |
Board Drafting vs. CAD Line Weights
- Board Drafting: Controlled using different lead grades (H, HB, F, etc.) or pen thicknesses (e.g., Rapidograph pens).
- CAD Drafting: Line weights are assigned in layers or plot styles and can be adjusted based on output scale.
2. Understanding Line Types
Different line types communicate specific details about objects, features, and relationships in a drawing.
Standard Line Types and Their Functions
| Line Type | Purpose |
| Continuous (Solid) | Visible object lines, structural elements |
| Dashed | Hidden features (holes, edges behind surfaces) |
| Phantom | Alternate positions, motion paths |
| Centerline | Symmetry axes, cylindrical features |
| Break Line | Interruption in views to shorten large objects |
| Section Line (Hatch Line) | Material indications in sectional views |
| Chain Line | Special treatments (heat-treated areas, limits) |
Board Drafting vs. CAD Line Types
- Board Drafting: Linetypes are manually created using different pencil pressures or stencils.
- CAD Drafting: Linetypes are predefined patterns in software (e.g., AutoCAD’s linetype library).
3. The Role of Scale in Line Weights
Scale affects how line weights appear in a drawing. A thick line in a 1:100 scale drawing may be inappropriate for a 1:10 detail view.
Key Considerations:
- Board Drafting: The drafter manually adjusts pen or pencil thickness.
- CAD Drafting: Line weights can be controlled by plot scale settings to ensure proper visual hierarchy.
4. Layering and Line Organization in CAD
Modern CAD systems allow drafters to assign line weights and types by layer, improving consistency.
Best Practices for Layering:
- Separate layers for visible lines, hidden lines, centerlines, dimensions, and annotations.
- Use color-coded layers to differentiate line functions.
- Assign global or by-object line weights for proper plotting.
5. Printing and Plotting Considerations
The transition from screen to paper can affect line visibility, requiring adjustments in plotting.
Challenges in CAD Printing:
- Line weights may appear too thick or thin based on printer resolution.
- Monochrome plotting vs. color plotting can alter readability.
- Drafters must preview line thicknesses before finalizing output.
6. Industry-Specific Line Weight Standards
Each drafting discipline applies line weights uniquely:
Architectural Drafting
- Thick lines for walls and structural elements.
- Dashed lines for overhead elements.
- Hatch lines to represent materials in sections.
Mechanical Drafting
- Centerlines to indicate axes of rotation.
- Phantom lines for moving parts.
- Section lines for cut materials.
Civil Drafting
- Property lines and roads drawn with specific linetypes.
- Dashed lines for underground utilities.
Electrical Drafting
- Continuous thin lines for wiring diagrams.
- Dashed lines for concealed wiring.
7. Transition from Board to CAD: Challenges and Adaptations
As CAD replaced manual drafting, drafters had to adapt:
- From hand-drawn hierarchy to digital layer control.
- From intuitive pencil pressure to automated line weights.
- From physical pen thickness to software-driven plotting settings.
Experienced drafters develop an eye for clarity, ensuring that even in a digital environment, line weights and types maintain the intent of traditional drafting principles.
Line weights and line types are the backbone of technical drawing, ensuring clarity and accuracy in design communication. While board drafting required manual control over these elements, CAD drafting introduced a more flexible and scalable approach. Understanding the balance between traditional techniques and modern software tools allows drafters to produce effective, readable, and professional drawings in any medium.