Adjust the rollers on the bat rolling device so that that bat is a tight fit. A tight fit means the bat will pass through when pushed, but not simply fall through with minimal force. There should be a simple lever on the side of the device that you crank to adjust the space between rollers.
Put the top of the barrel of your bat facing the opening between rollers. Run the bat through the device by pushing it through the rollers with your hands on the knob of the bat. Turn the bat about a quarter turn every time you pass it through the machine. This will allow the fibers of the composite or aluminum bat to break down. This break down of bat fibers allows the bat to be more flexible and hit farther.
Stop pushing the bat through the machine when the rollers are now touching the tape of the bat. When you have reached this point, pull the bat by the knob back through the device towards you. You should be turning the bat a quarter turn both ways through the rollers.
Continue to run the bat through the machine while turning. Repeat the process until you feel confident that the entire barrel has been exposed to the pressure of the rollers on the device. The bat should now be ready to test out.