This Coping Calculator is a handy tool that I use to create flat patterns for different pipes cuts, includes miter cut, pipes intersecting with variable angles or a pipe piercing through another pipe.

The Excel spreadsheet includes all configurations with a graph/flat pattern that looks like a bell curve. Just input the diameter and wall thickness, or angle of intersection.

Also included a Visual Basic (.dvb) program for Autocad that will take points from the Excel spread sheet and plot a flat pattern curve directly to Autocad.