Hi Rob-"sandpacking" worked well. Main hoop is done, and bends have less than 5% distortion. And , after putting my brain in gear, have answered the question in my first post. Have realised that the the reason I reached for the verniers after the first test bend, is that it didn't "look right" I also dug out a CAMS manual which says "...the centreline bend radius must be at least three times the tube diameter...where the tubing is distorted during bending, the ratio of minor to major diameter must be 0.9 or greater..." My tightest bend has a radius of about 6 inches, which obviously is close to the limit. My conclusion? What Mr CAMS said, but try to keep distortion to about 5%- thanks for your interest.