I have added two user defined functions (UDFs) to the IP2 spreadsheet to generate coordinates for a single  arc, or a series of arcs connected (if necessary) by straight lines.  The new version may be downloaded from:

IP2.zip

As an example of the use of the new functions, in conjunction with the IP (intersection) function, I have generated an animation showing the movement of two circular bearings, relative to a rotating tri-lobed shaft.  The tri-lobe is generated using the ArcSpline function, by defining the centre, radius, start and end angles, and number of segments for each of the six arcs:

A second arc-spline is then generated at 5 mm outside the first curve, representing the path that bearings of 5mm radius would follow, running around the outside of the inner spline.  The intersection point  of this outer spline can then be found using the IP function, and circles generated at these points, using the Arc function:

Full input for the two splines and two arcs is shown below.

The animation is then generated by recalculating the angular limits and centres of the spline curves, and the coordinates of the intersection of the circles and the X axis, for a series of small angle increments: