Thanks for the comments and advice Michael.

I tried this method and found it works well for curves but not so well for straight lines. If I use a projected polyline on the foot surface and try to sweep a circle I get a number of cylinders corresponding to the lines as boolean objects. Some of these cylinders will work with Boolean-Subtract but others either don't subtract at all or the base object is deleted rather than the cylinders.

Is this a limitation of the geometry library or am I likely to be doing something wrong?

Mal