Jaegers 6" f/10 "GJD" OTA Construction - The Main Tube (penetration of the tube wall)
 

Main tube being cut to proper size - 6. (Click to see an enlarged image.)

 
After continuously cutting around the main tube with shallow cuts in the groove, I finally cut through the main tube.  I will continue on cutting around the tubes circumference until I have cut the surplus free forming a precise perpendicular edge.