When I want to create a rounded corner, I use a Guide line for each side the use the arc to round the corner. When the arc is created it does not meet tangent to the sides of the rectangle, The ends of the Arc are depressed in slightly from each side and not tangent to the sides.

Use the Magenta inference. Place one guide to set your start point at the radius you want. Use the two point arc, first click at the intersection of the guide and the edge, then move to the other edge and when the arc turns magenta double click to finish.

What is the radius of the arc you are trying to draw?

Actually, the process Box describes will generate an arc whose mathematical ideal is tangent, but the first segments in the SketchUp representation will not be on the same lines as the sides. However, this isn’t really a problem because if the first segments were on the same line as the sides, the second ones would just do the same thing!

Umm mmm. And the more segments used the smaller the deviation at each change of angle.

It varies. If I am designing for 3D Printing it could be 1 mm. If I am designing for woodworking it could be 2 or 3 inches.

If you are modeling something that small, you should always scale up while initially creating the model and then scale back down to actual size when finished. Many SketchUp operations have trouble creating new geometry at very small sizes, but can preserve them when scaled back down.

And following on from @slbaumgartner comment, if you are working at 1mm type sizes you will get deformation at joints when vertices are too close together.

Good possibility at that size but it should do better at one inch or more.

Good point. I haven’t used that trick in a long time and forgot about it.