Fillet

The fillet command rounds a corner between two Line, Arc, or Polyline segments by inserting a tangent arc of a given radius, trimming (or merging) the picked entities back to where the arc begins.

Fillet works on Line, Arc, and Polyline entities — including a polyline’s own straight or arc segments.

Using fillet

1. Type fillet in the terminal or click the Fillet toolbar button.
2. Type the fillet radius and press Enter.
3. Click the first line, arc, or polyline segment — the portion you click determines which side of any intersection is kept.
4. Hover over the second entity — a dashed arc preview shows the resulting fillet. Move the cursor to the side you want to keep.
5. Click to apply.

  Before:                     After fillet (radius r):

  ──────────────              ──────────╮
                │                        ╰────
                │

Side selection for intersecting entities

When two entities cross each other, the fillet is applied on the corner defined by the click positions — the portion of each entity on the same side as the cursor is kept.

• Click near one end of the first entity to select that half.
• Move the cursor to the desired half of the second entity — the dashed preview updates live.

What the command creates

What comes out depends on what you picked:

• Two standalone Lines/Arcs, or any pair that doesn’t involve an open polyline: both trimmed back to the tangent points T1/T2, and a new Arc entity is inserted between them.
• Two segments of the same polyline sharing a corner vertex: no new entity — the fillet becomes part of the polyline itself. The corner vertex is replaced by the two tangent points, and the arc between them is stored as that edge’s bulge, exactly how a rounded polyline corner round-trips through DXF.
• Anything else involving an open polyline — two different open polylines, or an open polyline and a standalone Line/Arc: the two are merged into a single new polyline, each side kept up to its tangent point and joined by the fillet arc as one more bulge segment, replacing the original entities.

The inserted or extended arc inherits the current lineweight, color, layer, and linetype settings (or the polyline’s own, when it folds into one).

Corners with no real angle to round

If the two picked segments already meet tangentially at a shared vertex — a straight polyline corner, or a line running smoothly into a tangent-continuation arc segment — there’s no real corner for any circle to round. Fillet detects this and refuses with cannot fillet: no tangent circle fits there instead of drawing a stray loop.

Keyboard reference

Supported entities

Fillet vs Chamfer