A friend decided to build a new turbo manifold out of steam pipe/black pipe/nominal bore pipe and asked me to give him a hand with it, our first attempt at cutting the merge collector pipes didn't work very well so I came up with this method.

"This video is intended for entertainment purposes only"

The pipes were cut longer than required to allow trimming later, and as square as possible on the end that will locate against the stop.

A thick cutting disc was used at first to get a flatter cut but it took forever to cut and the disc had to be thrown out after cutting two pipes as it wasn't cutting anymore.

Thin discs cut much faster, last/work longer and can be made to cut fairly straight with care. A 9" grinder might work better but not many people own them (and probably fewer people should) so I didn't try using one.

The jig should be made as rigid as possible, but something thrown together like this gives reasonable results.

The symmetrical cuts are for turbochargers with square or round (V-band) inlets.

The offset cuts are for turbochargers with rectangular turbine inlets.

Trimming the entry to match the turbo flange would probably be better done with a grinder sled and flat board.

This method will work for any practical incidence angle, a similar method of angle determination could be used for bandsaws, mills and drop saws.

For a given number of primary pipes the alignment angle (90 degrees in this video) will be 360/number of primaries.