Abstract: A carriage for a hard disc drive polished as final finish has high surface precision of micron order. The finish surface is smooth, a cutting trace does not exist, and the surface layer is hardened uniformly by a magnetic material being hit by magnetic power. A cutting bur the edge of which is very tiny does not fall after installing the hard disc drive. The carriage for the magnetic head of the hard disc are not influenced by a temperature change and a seasonal change. The present invention forms a magnetic polishing brush by keeping magnetic abrasive material between magnetic poles in the carriage as a head arm member formed by extrusion molding or drawing for the magnetic head of the hard disc drive. The carriage of non-magnetic material as an aluminum part of HDD inserted in the above described magnetic polishing brush, is given reciprocation motion and vibration, thus the surface of the above described part is polished. The final finish is made by magnetic beam processing to polish or remove burs.

Abstract: The present invention provides a method for processing such as deburring, polishing and washing of surfaces of slits of a workpiece, having slits with narrow width from outer surface toward inside, with high accuracy and high efficiency. Magnetic abrasive material is retained in a magnetic field formed between magnetic poles 3 and 4, and magnetic brushes 5 are formed. A workpiece 1 made of non-magnetic material and having slits 1f with narrow width is placed in said magnetic brushes 5, and by relatively vibrating said magnetic poles and said workpiece, surfaces of the slits are processed. It is more effective to tilt the slit surface with respect to the magnetic field after the slit surface is arranged in parallel to the magnetic field.