Master the Cardinal Points
entities have some built-in editing points. The Circle and Polygon has four cardinal points. It might take a little hunting to find all four cardinal points on Circle and Polygon entities, but they are there. Adjust an Arc entity by moving the Endpoints or the Midpoint.
Note: when duplicating such entities - like when using Push/Pull - the properties also are copied. Position the Move Tool over a Cardinal Point and drag the point to change the radius.
Note²: Circle and Polygon entity cardinal points can be anywhere on an edge, not only on endpoints or midpoints. Where cardinal points are located depends on the orientation of the enity in the modeling space and the number of segments.
If you know the exact profile for a circular vessel-like shape, then draw a profile face and use the Follow Me tool
on a circular path. But if you are unsure of the profile – and want to play around with the shape – then moving the cardinal points on Circle entities may be something to try.
A lot can be done starting with just Circle. The Circle has four cardinal points. Three cardinal points are used in the following GIF animation.
You know an editing point is selected when the selection highlight color disappears.
Until the entity is disturbed by some non-uniform alteration, the editing points can be grabbed and dragged. When that happens, you can use the Scale tool to make similar adjustments shown in this animation. To symmetrically scale use the modified version of the Scale tool called Scale about Center. That's Scale + Ctrl (PC) or Scale + Option (Mac).
To rescale to a specific diameter, use the Scale tool to enter the diameter through the active Measurements box. Any number entered during a Move tool rescaling will be the amount of movement for the current procedure.
Uniformly rescaling a Circle entity with the Scale tool will not break a Circle entity. The Move tool can still grab a control point after a uniform Scale tool operation.
Read more about the Circle tool entity properties in SketchUp Knowledge Center.
Add a Little Flare
If you want to change the end of an existing cylinder, add a circle entity copy to the extrusion with Move + Ctrl (PC) then use the Move tool to adjust the edge and give the shape a little flare.
Additionally, extra circle entities can be created with the Offset tool. Those offset rings retain the circle entity cardinal points too.
Now adding a little flare with an Arc entity....