...only reference I can find for 'magneto welder' is for (old) engine driven machines which used a magneto for the ignition e.g. the Lincoln "Pipeliner" Model SA-200 (this one came up in a google search). If that was what you were asking I would have thought the direction of rotation of the magneto would be fixed to the rotation of the engine in some way (e.g. gears or a chain drive)?