Enter the diameter and thickness details of the tube to be cut as well as the mating tube and the angle at which they meet. In this case I measured it at 82 degrees. Print out the resulting pdf, cut out the template and then roll it onto the tube to be cut. A paint pen to marks the profile of the cut and I then use the 60 grit flapper wheel on the angle grinder to open the mouth of the tube. This photo was my first notch and it worked perfectly.