Just for clarification, Bernd, Mike's broach is for use under power, with the spindle turning. Contact with the workpiece causes the cutter to rotate in its holder. As the tool is at a very slight angle, each successive corner takes a little peck at the workpiece as it rolls into contact. You will have worked that out for yourself, but responses on another forum seem to show some folk thinkinking the tool is simply being rammed into a stationary workpiece, gouging out the corners as it goes in
I must ask Mike whether he feeds the tool in under power, or cranks the carriage along by hand.
Andy