When you change rail on a main line, you may need a different size tieplate for new rail. That machine will adz all the naked ties to have the save flat surface to receive a new tieplate. Another word, it will (sand)scrap the top of the tie in the plate area to level the plate cut wood in older ties. It is a rough wood grinder. Not needed on the narrow gauge where no plates are in use. Was it NARROW GAUGE Adzing machine? That would be rare.