Trouble Using the Center Snap

Working in Rhino 7 SR 12 on a model of a steam locomotive tender with rivets in the sides. I create the rivets using spheres Booleaned to the side. That works fine. When I try to find the center of the circular edge of the Booleaned rivet, the Center snap can’t seem to find the edge curve – which is a complete circle.

My work around to find the center of the Booleaned rivet has been to divide the rivet edge circle into four segments, then draw a line from the ends of the segments, then use the center of the line. Cumbersome but it works.

But now I’m going to redo the rivets on the tender side and using the work around is a lot more work if I have to do it over and over.

What am I doing wrong?

Attached is a tender side with the rivets. In black I have created a circle from a rivet edge. I have offset that circle. Neither honors the Center snap command to place a point in the center. Just below the tender side I have created a circle from scratch and placing a point with the Center snap command works just fine.

Best hopes for a little enlightenment,

Hilary Smith
Pacific Northwest
Circle Test 2021-12-15.3dm (5.4 MB)

Hi Hillary - the curve is a circle in theory but is not created as a true circle-

In Options > Modeling aids there is a setting for snapping to approximate arcs and circles - that will get it.




As always, you come through! Simple, beautiful solution.

Best thanks,