#Sketch: an overview

A sketch is the flat drawing the geometry of a part stands on. You draw an outline, give it constraints and dimensions, then turn it into a body: extrude, revolve, sweep. The sheet of a sketch is always flat: you move and zoom it, but do not turn it in space.

#How to start and finish

Sketch (the pencil, key K), then a click on a plane, a datum plane or a face of the part. Finish in the bar above leaves the sketch; a sketch you have just finished stays selected — the next part tool (Extrude, Revolve) takes it at once.

#The main rule: a sketch must be defined

The properties of the sketch on the right show how many degrees of freedom are left: "N constraint(s)/ dimension(s) short — the yellow points can still move". While there are more than zero, the sketch "floats": it looks right, but may move at the first edit. A defined sketch behaves predictably: change a dimension — exactly what it sets changes.

#What it is made of

• Entities — lines, circles, arcs, ellipses, splines, text.
• Constraints — rules between them: horizontal, vertical, coincident, parallel, perpendicular, equal, tangent, symmetric, point on a line, point on a circle.
• Dimensions — constraints with a number: a length, an angle, a radius, a diameter. The number can be a formula.

#How you draw

A tool is turned on with a button on the left or a key and stays in hand: you can draw several lines in a row. Esc puts the tool down. Text puts itself down as soon as the label is placed. If an icon is unclear, rest the pointer on it — the hint names it and its key.

Auto constraints (the magic wand in the bar above) add the obvious by themselves: draw a nearly horizontal line — get a horizontal. If one is wrong, delete it in the list of constraints on the right: hover a row — the constraint lights up, Del deletes it.

#Construction geometry

Key X toggles construction mode: such lines are dashed, stay out of the body's profile and serve as supports — centrelines, diagonals, circles for patterns.