#Ellipse

Key E. Three clicks: the first is the centre, the second the end of the major semi-axis (its length and direction, so the ellipse can lie at an angle), the third the minor semi-axis: its length is the distance from the click to the major axis. Until the third click the ellipse is only a picture; after it the ellipse enters the sketch and opens the width and height fields - Enter takes them, Esc leaves it as drawn.

#When you need it

An ellipse shows up where a round section is cut at an angle: a slanted branch pipe, a hole in a slanted wall, a decorative cut-out.

#What defines it

A centre and the ends of two semi-axes, major and minor. The direction of the major axis sets the tilt, so a tilted ellipse stays an ellipse instead of turning into a spline.

#Where it is used

Oval windows and hatches, eccentrics, transitions between round and flat. An ellipse is an exact curve, not an approximation made of arcs: a surface extruded from it stays smooth, and a machine cuts it without steps.

#Do not confuse it with a slot

A slot is two semicircles and two straight lines; its width is constant along its whole length. An ellipse narrows towards its ends. A screw guide needs a slot; a shape needs an ellipse.