This sketch is buggy on several levels. I projected to circular faces to a sketch and need a center line arc to be central to the circles, coincident and tangent. The arc either fails to dimension or it pulls the projected curves off of the faces when the last operation is adding the dimension depending on the order of operations. It seems like the only way to get the sketch to work properly is to add the dimension first. The issue may have something to do with the tangent constraints since there should not be able to have two of them along with the horizontal constraint.
