Filleting connects two objects with a smoothly fitted arc of a specified radius. Although in traditional paper-based drafting an inside corner is called a fillet and an outside corner is called a round, you can create both using FILLET.
You can fillet
Using FILLET is also a convenient method of creating an arc with a specified radius that is tangent to two selected objects. FILLET can be used to round all corners on a polyline using a single command.
If both objects being filleted are on the same layer, the fillet line is created on that layer. Otherwise, the fillet line is created on the current layer. The layer affects the fillet color and linetype.
The fillet radius is the radius of the arc that connects filleted objects. Changing the fillet radius affects subsequent fillets. If you set the fillet radius to 0, filleted objects will be trimmed or extended until they meet, but no arc is created.
You can use the Trim option to specify whether the selected objects are trimmed or extended to the endpoints of the resulting arc or left unchanged. By default, all objects except circles, full ellipses, closed polylines, and splines are trimmed or extended when filleted.
Depending on the locations you specify, more than one possible fillet can exist between the selected objects. Compare the selection points and resulting fillets in the illustrations.
Filleting a Line and a Polyline
For you to fillet line and polyline combinations, the line must intersect, or intersect when extended, one of the polyline line segments. If the Trim option is on, the filleted objects and the fillet arc join to form a single new polyline.
Filleting an Entire Polyline
You can fillet an entire polyline or remove fillets from an entire polyline.
If you set a nonzero fillet radius, AutoCAD LT inserts fillet arcs at each vertex where two line segments meet and the segments are long enough to accommodate the fillet radius.
If two polyline line segments are separated by one arc segment and the two line segments converge as they approach the arc segment, AutoCAD LT removes the arc segment and replaces it with a fillet arc.
If you set the fillet radius to 0, no fillet arcs are inserted. If two polyline line segments are separated by one arc segment, AutoCAD LT removes that arc and extends the lines until they intersect.
Filleting Parallel Lines
You can fillet parallel lines, xlines, and rays. AutoCAD LT ignores the current fillet radius and creates an arc that is tangent to both parallel objects and located in the plane common to both objects.
The first selected object must be a line or a ray, but the second object can be a line, an xline, or a ray. The fillet arc connects as shown in the illustration.
