Reference

FILLET in AutoCAD

Q: What is the shortcut for FILLET in AutoCAD?

F, then Enter or Space. The full name works too, and _FILLET in any language of AutoCAD.

Q: How do I fillet two lines?

Choose Radius, type it, then pick each line on the side you want to keep. Lines that do not meet are extended to the arc, and lines that cross are trimmed back to it. Two parallel lines are joined by a half circle, whatever the radius. A line and a polyline's segment are joined into one polyline.

Q: Why is FILLET not working?

It says why at the command line. “Fillet radius is too large” means the arc does not fit between the lines; “Lines belonging to polylines must be consecutive or separated by one segment” that two segments of one polyline are too far apart; text, blocks, dimensions and hatches are refused, objects at different heights are said to be non coplanar, and an object on a locked layer is not taken.

Q: How do I fillet the edges of a 3D solid?

Run FILLETEDGE: choose Radius if the radius is not the one it says, pick the solid's edges, then press Enter, and Enter again to accept the fillet. It works on 3D solids, which are still partial here.

How AutoCAD's FILLET (F) works, prompt by prompt: the radius, two lines, a polyline's corners, radius 0 and Multiple. Try it free in your browser.

FILLET rounds the corner between two objects with an arc of the radius you give, trimming or extending each object to it. Its first line says the mode and the current radius; then you pick the first object and the second, each on the side to keep, and the command ends. It takes lines, arcs, circles, ellipses, splines and the segments of a 2D polyline. Two lines need not meet: they are extended to the arc, as in AutoCAD. At radius 0, or with Shift held at the second pick, it makes a sharp corner instead.

Command: FILLET
Aliases: F
Panel: Modify
Try it: Open the editor, type F and press Enter.

At the command line

The engine draws it and writes its history as you would type it: the prompts in AutoCAD 2027's order, with the same option letters.

Command: FILLET
Current settings: Mode = TRIM, Radius = 0.00
Select first object or [Undo/Polyline/Radius/Multiple]: R
Specify fillet radius <0.00>: 15
Select first object or [Undo/Polyline/Radius/Multiple]: M
Select first object or [Undo/Polyline/Radius/Multiple]:
Select second object or shift-select to apply corner or [Radius]:
Select first object or [Undo/Polyline/Radius/Multiple]:
Select second object or shift-select to apply corner or [Radius]:
Select first object or [Undo/Polyline/Radius/Multiple]:

Four lines, then Radius 15 and Multiple: two corners rounded, two left sharp.

Options

`Undo` (`U`)

Takes back the last fillet, Polyline or radius given in this FILLET, one at a time. With nothing left to take back it says Command has been completely undone.

`Polyline` (`P`)

Asks for a 2D polyline and rounds every corner where two of its segments meet, in one step, then says how many it filleted and how many it passed over, parallel or too short for the radius. A rectangle drawn with RECTANG is such a polyline.

`Radius` (`R`)

Asks for the radius, also offered at the second prompt. It is the drawing's (FILLETRAD): the next FILLET starts with it, and it is saved with the drawing. 0 makes sharp corners; a negative radius is refused.

`Multiple` (`M`)

Asks for the first object again after each fillet, so you round corner after corner without starting over, until Enter.

What it does not do yet

Trim: the objects are always trimmed or extended to the arc, as with TRIMMODE 1, AutoCAD's default; No trim is not offered. The arc does not take the second object's linetype scale, as no object has one of its own here. Before the click, the tooltip shows the prompt rather than why a pair cannot be filleted, and no padlock marks an object on a locked layer. A few rare pairs of ellipses or splines end otherwise: a closed spline with a line at radius 0, an arc that only touches an ellipse's offset, and such a pair in a tilted plane.

What it does and still lacks, in detail (in English)

Questions

What is the shortcut for FILLET in AutoCAD?

F, then Enter or Space. The full name works too, and _FILLET in any language of AutoCAD.

How do I fillet two lines?

Choose Radius, type it, then pick each line on the side you want to keep. Lines that do not meet are extended to the arc, and lines that cross are trimmed back to it. Two parallel lines are joined by a half circle, whatever the radius. A line and a polyline's segment are joined into one polyline.

What does a fillet radius of 0 do?

It makes a sharp corner: each line is trimmed or extended until they meet, and no arc is drawn. To make one sharp corner without changing the radius, hold Shift as you pick the second object.

Why is FILLET not working?

It says why at the command line. Fillet radius is too large means the arc does not fit between the lines; Lines belonging to polylines must be consecutive or separated by one segment that two segments of one polyline are too far apart; text, blocks, dimensions and hatches are refused, objects at different heights are said to be non coplanar, and an object on a locked layer is not taken.

How do I fillet the edges of a 3D solid?

Run FILLETEDGE: choose Radius if the radius is not the one it says, pick the solid's edges, then press Enter, and Enter again to accept the fillet. It works on 3D solids, which are still partial here.