The EMAG Grinder HG 208 CD – External and Internal Machining in a Single Set-Up The External Cylindrical Grinder HG 208 CD machines hollow shafts with a length of up to 400 mm (16 in). The Center Drive Grinder is equipped with two internal and two external grinding spindles mounted on two compound slides that each features a B-axis. This configuration allows the internal grinding of bores, end faces and tapers.