Hold the end of one pipe on a piece of paper (or use a coin the same
size if possible, and draw a circle. Fold the paper in half so the
arcs line up and cut out the circle. Wrap that around the pipe, mark,
cut, and grind to suit. Flop the cut piece over and weld it.
Easy enough?



Easy enough, but it won't work.

Your way, you'll get an arc (a half-circle, actually) with a chord length equal
to the pipe diameter, and with the arcs tangent at 90 degrees to the chord.

The correct pattern will be an arc with a chord length of pi divided by twice
the diameter, and with the arcs tangent at 45 degrees.

Instead, I'd make the 45 degree cuts on the end of the vertical piece first,
and make a pattern from that. Or, butt the pieces together and scribe the
joint.

John Martin