#Spline

Key N. A smooth curve through points.

#How to draw it

Press Spline and click the knots in order; a double-click places the last one and ends the curve. A click on the first knot closes the curve into a loop. A knot clicked on a point, a line, a circle or an axis is tied to it.

Click the curve to select it: its tangent handles appear, and the handle under the pointer lights up. Drag a handle to bend the curve at its knot; drag a knot to move it — the curve follows. A spline together with lines or arcs, or crossing itself, closes regions that Extrude and the other part tools take.

#Mind the definition

Each knot has two degrees of freedom, and pinning a spline down entirely with dimensions is next to impossible. That is fine for a styled shape and bad for a working outline: where a function sets the shape (a surround, aerodynamics, ergonomics), a spline fits; where a size does (a fit, a hole, a joint), lines and arcs are better.

#If it did not work

A contour with a spline does not extrude — the ends of the spline do not meet their neighbours. Draw the spline from the end of a line and click its last knot on the end of the next one, or pin them with the Coincident constraint.