Day 16
Editing
70 XP

FILLET + CHAMFER

Round or bevel corners.

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Learning objective

By the end of this lesson you can round corners between two lines with FILLET and bevel them with CHAMFER, each at a chosen size.

What FILLET + CHAMFER is

FILLET replaces a sharp corner between two objects with a smooth arc of a chosen radius. CHAMFER replaces it with a straight bevel cut at chosen distances.

Why and when you use it

Manufacturing parts almost never have perfectly sharp corners — they're rounded (filleted) or bevelled (chamfered) for safety, strength and casting. Use FILLET and CHAMFER to model real corners.

Where to find it in the AutoCAD interface

Ribbon
Home tab → Modify panel → Fillet / Chamfer dropdown.
Menu
Modify menu → Fillet / Chamfer.
Command line
Type FILLET or CHAMFER and press Enter.
Alias / shortcut
F for FILLET, CHA for CHAMFER.

Key vocabulary

Radius
The size of the rounded corner created by FILLET.
Distance
How far back from the corner each line is cut by CHAMFER.
Trim mode
Whether AutoCAD shortens the source lines back to the new corner. On by default.

Before you start

  • Draw two intersecting (or near-intersecting) lines.
  • Decide on a radius (FILLET) or distance (CHAMFER) before starting the command.
  • Turn OSNAP off if you've been getting accidental snap picks on nearby geometry.

Step-by-step instructions

  1. 1
    Start the FILLET command
  2. 2
    Set the radius
  3. 3
    Pick the two lines
  4. 4
    Start the CHAMFER command
  5. 5
    Set the distances
  6. 6
    Pick the two lines to chamfer

Visual reference

Common mistakes & fixes

  • Radius left at 0 — the corner just becomes sharp.
    Fix: Type R, Enter, then a real radius before picking the lines.
  • Clicking the wrong end of a line.
    Fix: Click closer to the end you want to keep — the other end gets trimmed.
  • Trim mode off without realising.
    Fix: Type T, Enter, T, Enter to turn trimming back on so the source lines are shortened to the new corner.

Troubleshooting

Nothing happens after I pick two lines.Show
Cause: Radius is 0 and they don't quite meet.
Fix: Set a non-zero radius, or extend the lines so they cross first.
Lines weren't trimmed.Show
Cause: Trim mode was set to No trim.
Fix: Inside the command type T, Enter, T, Enter (Trim on).

Practice exercise

Fillet all corners of a rectangle with R15
  1. Draw a rectangle with REC.
  2. Type F, Enter.
  3. Type R, Enter. Type 15, Enter.
  4. Type P, Enter (Polyline option) and click the rectangle.
Success looks like: Every corner of the rectangle is rounded with a 15-unit arc in one click.

Pro tips & related commands

Pro tips
  • Inside FILLET, use the Polyline option (P) to fillet every corner of a closed polyline at once.
  • Hold Shift while picking the second line to apply a radius of 0 — quick way to clean up a corner without changing the stored radius.
  • FILLET works on parallel lines too — it joins them with a half-circle.
Related commands
  • BLEND
    Connect two open curves with a smooth spline.
  • TRIM(TR)
    Cut back overshooting lines manually.
  • EXTEND(EX)
    Lengthen lines to meet another.
Lesson quiz
0/2 correct

Score at least 2/2 to unlock lesson completion.

1. What does FILLET do?
2. If FILLET radius is 0, the corner becomes…

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OFFSET + MIRRORARRAY + Dimensions Review

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