The amount of spin you place on a golf ball directly affects the success or failure of a variety of shots. For example, you must impart just the right amount of side spin on the ball to hit a controlled fade or draw. When you’re hitting an approach shot, you typically want as much backspin as possible on the ball -- particularly if you’re hitting from the rough -- so the ball won’t bounce or roll off the green. A rough-surfaced club can help impart backspin on the ball.
Friction is a key element that helps create backspin during a golf shot. Friction is defined as the force that resists movement between objects that come in contact with each other. The smoother the surfaces of the objects that collide or are rubbed together, the less friction created. Conversely, rougher surfaces produce greater amounts of friction.
Club Face Friction
If the golf ball and club face were both smooth surfaces there would be little friction, so the ball would naturally slide up the angled club face on impact. The resulting shot would have little backspin. A dimpled golf ball is, obviously, not a completely smooth surface. Additionally, the club’s grooves are designed to apply friction to slow the ball’s progress up the club face. This results in a greater amount of backspin. Likewise, a club head designed with a rough face adds even more friction, which further resists the ball’s ability to climb up the club face and therefore adds even more backspin to the shot.
Because the benefits of backspin can be so great on certain shots, the United States Golf Association limits the degree of roughness a club head may contain. Appendix II, Section 5b, of the Rules of Golf states that with a few exceptions the roughness of a club’s impact area “must not exceed that of decorative sandblasting, or of fine milling.” Exceptions to this rule allow for grooves, punch marks and certain decorative markings on the club face. The impact area on a typical club is the area in which grooves are cut.
The USGA’s equipment guidelines further refine the definition regarding allowable roughness on the club head’s surface. Club faces conforming to USGA regulations may not have a roughness measured at more than 180 micro inches. On milled club heads, the crest-to-trough depth cannot be greater than 0.001 inch, which equals 0.025 millimeter.