But the mounting flange has to be screwed down in position. The mounting holes that are required to mount the HF unit are the same as the small screws that are used to secure the plate for the routing. Once the hole is cut then drill through the screw holes and countersink for the mounting screws.
The next pics are of the rounding over cutter with a temporary extension baseplate on the router. I had to fit this to allow the cutter to sit in the correct position and also to give some extra stability.
It all went very well considering the diameter of the cutter. Two passes did it and almost no break out at the end of the cut.