Close an arc to make a circle or ellipse; connect splines

Starting with AutoCAD 2006, you can use the JOIN command to join objects that are colinear, meaning that they’re along the same line. Usually, you use JOIN to join lines or polylines. For example, you may have broken a line and now you need it whole again. The command fills in gaps, if necessary.

You can also use the JOIN command to join arcs that are along the same circumference or elliptical arcs that are along the same elliptical circumference. Just select an arc or elliptical arc and use the cLose option.

You can even join splines, as long as they don’t have any gaps. Help says that you can join helixes, but this didn’t work for me. Perhaps the language in Help is misleading, because I was able to join a helix with a spline.

Here is the result in a Top view:

Even cooler, here it is in Souteast Isometric view: