Discrimination Effectiveness of Speech Cepstral Features

This invention provides a method of and apparatus for punching apertures in the walls of square sectioned steel tube. An elongated square sectioned mandrel is supported horizontally by and is connected at a rear end to roller decking so that a square tube can be fed onto the mandrel and can be used to feed the tube off the mandrel step by step, while between steps the tube is punched at the front end of the mandrel by a punch die on a punch head which moves laterally of the mandrel and into a punch recess in the mandrel. The punch head also has a guide pin which engages a guide recess in the mandrel before the punch die engages the punch recess to ensure that the punch die and punch recess are accurately aligned and that the apertures will be evenly spaced along the length of the tube.