CONTOURING WHEELS & ROLLS Machining tapers, chamfers, grooves, and other surface configurations into wheels, rollers, and other round parts all fall into the general category of contouring. Tools for grooving the O.D.s of hard urethanes -- 95A to 75D -- all have the same basic tool geometry. We have found that a 10 to 20 degree front rake works well with no top rake. Use high rpm (depending on the diameter of the work place) and moderate hand feeds. The tool works best when positioned .025 to .075 inches below the center of the work piece. The chips should come off in a continuous ribbon. Try to keep the chip from wrapping around the work piece. If this occurs, stop, remove the urethane that wrapped around the work. Reduce the feed rate. Safe fixturing of parts when contouring is very important. When contouring urethanes softer than 95A, use a tool with 15 to 30 degrees of top rake. Lathe speed depends on the O.D. of the part. In general, high rpm works best. Feeds should be slow until experience is achieved. Note: When machining urethane, wear a full face mask. A full discussion of all aspects of machining is available free upon request. Ask for "A Guide to Machining Urethane" by Terry Zegar. NEXT: Milling Contouring tool. Secondary operations on a lathe are often more cost effective than closed molding.