How to Trim Lines in Fusion 360

Trimming lines in Fusion 360 is a fundamental skill for cleaning up your sketches, removing unwanted segments, and creating precise geometries for your 3D models. The Trim tool allows you to easily cut away parts of lines, arcs, and circles that extend beyond intersection points or are simply no longer needed.

Understanding the Trim Tool

The Trim tool is incredibly useful for refining complex sketches by eliminating overlapping or excess sketch entities. It works by removing segments of a sketch entity up to the nearest intersecting point with another entity.

Step-by-Step Guide to Trimming Lines

Follow these simple steps to effectively trim lines and other sketch geometry in Fusion 360:

Enter Sketch Mode: Before you can trim, you need to be in an active sketch. If you're not already, create a new sketch or edit an existing one. You'll see the Sketch contextual tab appear in the toolbar.
- Tip: Access the Create Sketch command from the Solid or Surface tab, or right-click on a face/plane and select Create Sketch.
Activate the Trim Tool:
- Navigate to the Sketch tab in your toolbar.
- Click on the Modify dropdown menu.
- Select Trim (or simply press the keyboard shortcut T).
Hover and Preview: Once the Trim tool is active, move your mouse cursor over the sketch geometry you wish to modify. Fusion 360 will provide a visual preview, highlighting the segment that will be removed if you click. This allows you to confirm which part of your sketch will be trimmed before you commit.
Click to Trim:
- Click once on the specific segment of the line, arc, or circle that you want to remove.
- The highlighted segment will disappear, and the sketch will update.
Continuous Trimming: A key advantage of the Trim tool in Fusion 360 is its persistence. After trimming a segment of sketch geometry, the Trim tool remains active. This means you can continue to click and trim away other unwanted parts of your sketch without needing to re-select the tool each time, streamlining your workflow considerably.
Exit the Trim Tool: Once you've finished trimming, press the Esc key on your keyboard, or select another command from the toolbar, to deactivate the Trim tool.

Essential Tips for Effective Trimming

Intersections are Key: The Trim tool primarily works at intersection points. If a line doesn't intersect another sketch entity, it cannot be trimmed using this method.
Watch for Constraints and Dimensions: Trimming can sometimes break or modify existing constraints and dimensions. Fusion 360 will often warn you or automatically adjust related elements. Be mindful of how your trims might impact other parts of your sketch.
Undo is Your Friend: If you accidentally trim too much or the wrong segment, simply use Ctrl+Z (Windows) or Cmd+Z (Mac) to undo the last action.
Combine with Other Tools:
- Extend (E): Use the Extend tool to lengthen a sketch entity to the nearest intersecting entity, which can create new intersection points for trimming.
- Break: If you need to split a single line into two separate entities without removing a segment, the Break tool (under Modify) is a better option.
Projected Geometry: When trimming projected geometry, the original projected line might remain. You may need to delete the original projected line or move it to a construction layer if it's no longer needed.

Trim vs. Other Modify Tools

Understanding the differences between trimming and other related sketch modification tools can significantly improve your sketching efficiency.

Tool	Hotkey	Purpose	Behavior
Trim	T	Removes a segment of sketch geometry between two intersection points.	Click to remove. Stays active for continuous trimming.
Extend	E	Lengthens a sketch entity to the nearest intersecting entity.	Click the entity to extend.
Break		Splits a single sketch entity into two at a specified point.	Click on an entity to place a break point. No geometry is removed.
Delete	Del	Completely removes a selected sketch entity or a part of it.	Select the entity and press `Delete`. Doesn't require intersections.

By mastering the Trim tool and its companions, you can create clean, precise sketches that form the foundation for accurate and robust 3D designs in Fusion 360. For more in-depth information on sketching tools, refer to the official Fusion 360 documentation (example link).