With the circle spline selected there should be a section in the Object tab of the Attributes Manager that includes an “Intermediate Points” drop down menu as well as a Number, Angle and Maximum Length property. These control how many intermediate points are used along the spline.
The default is Adaptive which will add intermediate points to keep the change in angle along a curve at or below the Angle value (a lower Angle value means more intermediate points).
Depending on what you need the extrusion for you may be fine using Adaptive with a lower Angle value, or you might want to use another option.
For most purposes I like the ‘Natural’ option. This takes a Number value to define how many intermediate points there are in between each pair of spline points.
If you make a circle spline editable you’ll see that the resulting spline is made of 4 points. So if you leave the Number value at 8 in the Natural mode you should end up with 36 subdivisions in your extrusion (4 spline sections * 8 intermediate points per section = 32 + 4 original sections = 36). If you increase the Number value to 16 then you would end up with 68 subdivisions.
The Uniform intermediate points mode is similar to Natural only the distribution of the intermediate points should be more… uniform 🙂 With the Natural mode points should be clustered around areas that need more detail where as with the Uniform mode they will be evenly distributed across each spline segment.
Darby Edelen