1.4Trim, extend, fillet, chamfer & break
A "raw" drawing is rarely clean: lines cross, stick out, or don't meet. The cleaning and finishing commands fix all of this: Trim (TRIM/TR — cut what sticks out), Extend (EXTEND/EX — stretch up to a boundary), Fillet (FILLET/F — join with an arc or a sharp corner), Chamfer (CHAMFER/CHA — cut a corner) and Break (BREAK/BR).
These commands turn an approximate drawing into an impeccable technical drawing. Fillet with a radius of 0, for example, cleanly closes two lines into a sharp corner; with a radius, it creates a rounded fillet. Trim/Extend are so complementary that AutoCAD lets you switch from one to the other by holding Shift. A clean drawing, without overruns or gaps, is the mark of a professional.
Section vocabulary
- Trim (TRIM / TR)
- Cut the part of an object that extends beyond a cutting edge.
- Extend (EXTEND / EX)
- Stretch an object until it meets a boundary edge.
- Fillet (FILLET / F)
- Join two objects with an arc of a given radius (rounding), or in a sharp corner if radius = 0.
- Chamfer (CHAMFER / CHA)
- Join two objects with a beveled segment (cut a corner) according to given distances.
- Break (BREAK / BR)
- Remove a portion of an object between two points, or split it.
Fillet (FILLET / F) with a radius of 0 is used to…
In practice — Cleaning and finishing a drawing
- On a drawing that sticks out, use Trim (TR): select the cutting edge then the parts to remove.
- On lines that are too short, use Extend (EX) up to an edge; hold Shift to switch Trim/Extend.
- Close two lines in a sharp corner with Fillet (F) radius 0, then create a rounded fillet with a radius.
- Cut a corner with Chamfer (CHA), and remove a portion of a line with Break (BR).
Key points to remember
- Trim (cut what sticks out) and Extend (stretch up to an edge): complementary (Shift to switch).
- Fillet: rounded fillet (radius), or sharp corner (radius 0).
- Chamfer: cuts a corner beveled according to distances.
- A clean drawing, without overruns or gaps, is the mark of a professional.
Frequently asked questions
Fillet with radius 0, what is it for?
It's a very handy trick: Fillet (F) with a radius set to 0 cleanly joins two lines into a sharp corner, automatically extending or trimming what is needed. It's often faster than Trim + Extend to close a corner. With a non-zero radius, the same command creates a rounded fillet. Remember this double use: Fillet is one of the most used tools.
Trim doesn't work / trims the wrong side, why?
In recent versions, Trim/Extend have a "quick" mode that uses all objects as cutting edges by default: you simply click the part to remove. If the behavior surprises you, check the command mode (command line options) and click correctly on the portion to remove. Holding Shift during Trim allows you to extend, and vice versa — handy when you started the wrong command.