How to mirror a block in AutoCAD?

Mirroring a block in AutoCAD is a straightforward process that allows you to create a symmetrical reflection of an existing block across a specified axis. You can flip objects about a specified axis to create a symmetrical mirror image.

Understanding the Mirror Command in AutoCAD

AutoCAD's MIRROR command is essential for creating mirrored copies of drawing entities, including blocks. You flip objects about an axis called a mirror line to create a mirror image. This means you define an imaginary "mirror line" within your drawing, and the selected block will be reflected across this line to create its symmetrical counterpart.

To specify this temporary mirror line, you enter two points. These two points define the orientation and position of the axis of reflection. After selecting the blocks and defining the mirror line, AutoCAD provides an option to erase or retain the original objects, giving you control over whether the original block remains in your drawing or is replaced by its mirrored twin.

Step-by-Step Guide to Mirroring a Block

Follow these precise steps to mirror a block in AutoCAD:

1. Initiate the Command:
   • Type MIRROR (or its command alias MI) into the command line and press Enter.
2. Select the Block(s):
   • At the "Select objects:" prompt, click on the specific block(s) you wish to mirror. You can select multiple blocks simultaneously if needed.
   • Once all desired blocks are selected, press Enter to confirm your selection and proceed.
3. Define the Mirror Line (First Point):
   • AutoCAD will then prompt you to "Specify first point of mirror line." Click a point in your drawing that will serve as one end of your reflection axis. For precision, utilize AutoCAD's object snap (Osnap) features to snap to existing geometry like endpoints, midpoints, or centers.
   • Example: If you want to mirror a block horizontally, your two points for the mirror line should define a vertical line. Conversely, for a vertical mirror, your points should define a horizontal line.
4. Define the Mirror Line (Second Point):
   • Next, you'll be asked to "Specify second point of mirror line." Click to define the other end of your reflection axis. The imaginary line connecting the first and second points you specified becomes your mirror line.
   • Tip: Activating Ortho Mode (by pressing F8) before specifying the second point can help you draw a perfectly horizontal or vertical mirror line, ensuring a precise symmetrical reflection.
5. Choose Source Object Retention:
   • Finally, the command line will display: "Erase source objects? [Yes/No] ".
     • Type N (or simply press Enter, as No is the default option) to retain the original block and create a mirrored copy alongside it.
     • Type Y and press Enter to erase the original block, leaving only the newly created mirrored version.

For a quick overview of the command flow, refer to the table below:

Practical Insights and Considerations

• Precision with Osnaps: Always leverage AutoCAD's object snap (Osnap) functionalities (e.g., Endpoint, Midpoint, Center) when defining your mirror line. This ensures that your mirrored block is perfectly aligned and symmetrical with respect to existing geometry.
• MIRRTEXT System Variable: When blocks contain text or attributes, mirroring them might result in the text appearing backward or inverted. AutoCAD's MIRRTEXT system variable controls this behavior:
  • Set MIRRTEXT to 0 (zero) to prevent text within blocks from being mirrored. The text will retain its original orientation.
  • Set MIRRTEXT to 1 (one) to mirror the text along with the block (this is the default setting).
  • To change this, type MIRRTEXT in the command line, press Enter, then type 0 or 1, and press Enter again.
• Block Definition vs. Instance: Mirroring a block instance does not alter the original block definition stored in your drawing. It simply creates a new instance of that block that is reflected.
• Efficiency in Design: The MIRROR command is invaluable for creating symmetrical elements efficiently, such as furniture layouts, architectural facades, or intricate mechanical components, significantly reducing drawing time and ensuring accuracy.

By mastering the MIRROR command, you can efficiently create symmetrical designs and manipulate blocks in AutoCAD, significantly enhancing your productivity and design capabilities.