I want to make a plane tangent to the surface of the cylinder extrusion so that I can put little domes on it for decoration. I keep getting this error message when I try to make a tangent plane. What did I do wrong?
As the error message says, you haven't selected enough to define the plane.
Tangent could be at an infinite amount of points on a cylindrical face.
You need to define a point (sketch, 3D sketch, reference point), or in your case, if the cylindrical face is normal to the XZ plane, you could pick the XY plane and use parallel to fully define the plane.
You need to add another constraint, for example parallel to front plane. As you have it the plane could rotate anywhere around the cylinder
You need to give more input to the software. There is an infinity of planes that tangency the cilinder, each of them tangency the cylinder in a different point.
For example, 4 planes in the first print, all of them are tangent to the cylinder.
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