Bat Rolling and the Science behind it.

Composite Bats are made by pressing layers of resin and fiber together (see video). The resin can be broken up in between each layer of composite by Bat Rolling. The bat is placed in between 2 rollers and pressure is added to flex the bat in order to break up the resin. As the resin breaks up the fiber is free to flex which gives the bat more of a trampoline effect. This trampoline effect equates to greater batted ball speeds. This effect can be achieved with aluminum or alloy bats also. The metal becomes more malleable which also causes a trampoline effect and more distance to the batted ball.

Perpendicular bat rolling was the first type of bat rolling machine to be manufactured. Perpendicular bat rolling was the industry standard in the infancy of rolling. The Perpendicular method breaks the resin up in 1/4 of an inch stripes along the barrel at maximum pressure (see fig 1-2). As bat rolling evolved so did the machines and the parallel roller was created. The parallel roller is able to put consistent pressure along the entire circumference of the barrel to break up resin completely (see fig 3). For this fact perpendicular rolling followed by parallel rolling has become the bat rolling standard.

Parallel rolling is optimized with a 6 inch roller. Most slowpitch softball bats have a 9 inch sweet spot (see fig 4). Parallel rolling will cause the barrel to flex about 1 1/2 inches past the roller at maximum pressure (see fig 5). The flex should not extend into the end cap area or the taper area for risk of damaging the integrity of the bat. The 6 inch roller will not damage the taper area or end cap area but a larger roller has the potential to flex the composite material in these areas and cause structural problems with the composite.