How to Create, Edit, and Load Hatch Patterns in AutoCAD

In AutoCAD, "opening a hatch file" can refer to several related actions: creating a new hatch, editing an existing hatch, or making custom hatch patterns (typically .pat files) available for use. Hatch patterns are essential for representing materials and areas in technical drawings.

Creating a New Hatch in AutoCAD

To apply a new hatch pattern to an enclosed area in your drawing, you use the HATCH command. This process involves defining the boundary and selecting your desired pattern.

Access the HATCH Command:
- Navigate to the Home tab on the AutoCAD ribbon.
- Locate the Drawing panel.
- Click on the Hatch icon. Alternatively, type HATCH or H in the command line and press Enter.
Define the Hatch Boundary:
- Once the HATCH command is active, AutoCAD will typically prompt you to "Pick internal point".
- Move your mouse cursor inside an enclosed area (a closed polyline, circle, or any combination of objects that form a watertight boundary) within your drawing.
- Click to select the area where you want the hatch to appear.
- Important: You must click inside an enclosed area. After making your selection, press Enter to confirm the boundary.
Adjust Hatch Settings:
- After selecting the boundary, a contextual Hatch Creation ribbon will appear.
- You can now customize various aspects of your hatch:
  - Pattern: Choose from predefined patterns (e.g., ANSI31, BRICK, GRASS) or custom patterns.
  - Scale: Adjust the pattern's size. If the hatch appears solid or invisible, try increasing or decreasing the scale.
  - Angle: Rotate the hatch pattern.
  - Origin: Define the starting point of the hatch pattern.
  - Annotative: Enable annotative scaling for the hatch.
  - Island Detection: Control how internal boundaries (islands) are hatched.

Editing Existing Hatch Patterns

Modifying an existing hatch is straightforward, allowing you to quickly update its appearance.

Select the Hatch: Click on the hatch entity in your drawing.
Access Hatch Editor: Upon selection, the Hatch Editor contextual ribbon will automatically appear, offering the same customization options as during creation (Pattern, Scale, Angle, etc.).
Use the Properties Palette:
- Alternatively, with the hatch selected, open the Properties palette (type PROPERTIES or PR and press Enter).
- Here, you can modify all hatch properties, including color, transparency, pattern type, scale, angle, and more. This provides a comprehensive overview and control over the hatch's attributes.

Loading and Using Custom Hatch Patterns (.pat Files)

If you have a custom hatch pattern defined in a .pat file, you don't "open" it in AutoCAD like a drawing file. Instead, you make it accessible to AutoCAD so it appears in your list of available patterns.

Understand .pat Files:
- A .pat file is a plain text file that contains the geometric definitions for one or more hatch patterns. These files can be created using a text editor like Notepad.
- For example, a simple pattern might look like this:
```
*MYPATTERN, My custom pattern
0, 0,0, 0,0.1, 0.05,-0.05
90, 0,0, 0,0.1, 0.05,-0.05
```
Make Custom Patterns Accessible:
- Method 1: Place in Support File Search Path (Recommended)
  - The most common method is to copy your .pat file(s) into one of AutoCAD's Support File Search Path folders.
  - To find these paths:
    1. Type OPTIONS in the command line and press Enter.
    2. Go to the Files tab.
    3. Expand "Support File Search Path."
    4. Copy your .pat file into one of the listed folders (e.g., C:\Users\<username>\AppData\Roaming\Autodesk\AutoCAD 20XX\RXX.X\eng\Support).
  - After placing the file, you might need to restart AutoCAD, or you can use the REGEN command.
- Method 2: Add Custom Hatch Location
  - From the Hatch Creation or Hatch Editor ribbon, click the Settings button (gear icon) in the Options panel.
  - In the Hatch and Gradient dialog box, go to the Type and Pattern panel.
  - Click the "..." button next to "Custom Pattern" to browse for your .pat file. This temporarily adds the path for that specific session.
- Method 3: Using ADDCUSTOMHATCH (for older versions or specific needs)
  - Some third-party tools or older workflows might use commands to directly load .pat files without placing them in the support path, though this is less common with modern AutoCAD.
Use the Custom Pattern:
- Once the .pat file is in a recognized path, initiate the HATCH command.
- In the Hatch Creation ribbon, under the Pattern section, change the "Type" to Custom.
- Your custom pattern(s) will now appear in the dropdown list, identified by the name defined in the .pat file (e.g., MYPATTERN).

Common Hatching Tips and Troubleshooting

Closed Boundaries: Hatches require perfectly closed boundaries. Even tiny gaps will prevent a hatch from forming or cause it to spread throughout the drawing. Use commands like BOUNDARY (BO) to create a closed polyline from existing geometry, or use PEDIT (PE) to join lines into a polyline.
Scale Issues: If your hatch pattern looks like a solid block or is invisible, adjust the scale. A very small scale can make lines merge, while a very large scale can make lines too far apart to be seen.
Island Detection: Experiment with the "Normal," "Outer," and "Ignore" island detection styles in the Hatch Editor to control how internal objects are treated within a larger boundary.
Associative Hatch: By default, hatches are associative, meaning they update automatically if their boundary objects are modified. You can toggle this behavior in the Hatch Editor.

Comparison of Default vs. Custom Hatch Patterns

Feature	Default/Predefined Hatch Patterns	Custom Hatch Patterns (.pat files)
Availability	Instantly available within AutoCAD	Require `.pat` files to be loaded or placed
Source	Built-in to AutoCAD	Created by users or obtained from third parties
Flexibility	Limited to predefined designs	Highly flexible; can represent any repeating pattern
File Type	N/A (internal definition)	Plain text `.pat` files
Use Case	Standard architectural, engineering, and common fills	Unique material representations, specialized symbols

By understanding these methods, you can effectively utilize and manage hatch patterns to enhance your AutoCAD drawings.