tornire una sfera

[mklotz]

There are other uses for a tool of this design...

With a longer tool extension, the tool can turn concave depressions in a workpiece.

To turn a true sphere the rotary axis of the tool must intersect the rotational axis of the lathe. By offsetting the tool axis, the tool can be made to turn ogives. Ogives are often the shape of a rocket nose cone. Some arrow points and propeller spinners use the shape as well.

I discussed an incremental method of turning ogives here...

How to turn ogives

You may want to examine that discussion to understand the mathematics of the ogive.