Pulley History

• Pulleys initially were used to transfer rotating motion from one place to another. They often used continuous strips of leather, rope or cable. After John Gates developed V-belts in 1917, the use and popularity of pulleys grew exponentially because they were capable of transferring considerable power at high speeds. This led to universal use of the pulley-belt strategy in automobiles. V-belts became the drive of choice for many power tools, powered farm and lawn implements, and appliances such as washers and dryers. Cogged timing belts have lateral teeth that fit into teeth in sprocket pulleys to provide positive drives that fix the exact number of turns each pulley will make when they are used together.
  
  

Selecting Pulley-Belt Systems

• Pulley-belt systems work especially well on higher-speed and low- to moderate-torque applications. When selecting a set, first consider the number of shafts being connected, along with the relative speeds in RPM, or revolutions per minute.
  The empirical formula for drive belts is that smaller pulleys driving larger pulleys will lose speed and gain torque proportionally to the driven pulley diameter, divided by the driving pulley diameter. An 8-inch pulley driven by a 2-inch pulley will multiply its torque four times, but with a resulting quartering of shaft velocity. A 2-inch pulley driven by a 4-inch pulley will double the rotational speed while halving the torque.
  Also consider shaft sizes and attachment options. Some pulleys fasten to shafts with a set screw, though greater torque demands a keyway, or even splines for some applications. Other high-torque options use flat cogged timing belts with teeth that fit into tooth-like grooves in the pulley.
  
  

Implementing Pulley-Belt Systems

• Although most belts are more forgiving than chain drives regarding slight misalignment, proper alignment assures efficient power transfer and long life for belt systems. Take belt tension into consideration. Most systems use spring-loaded adjustment brackets, tension arms and threaded adjustment methods. This assures that maximum torque can be transferred without screeching or slipping.
  Over-tightening will result in premature wear of the belt and other drive line components. Where fingers or other body parts might have access to pulley-belt drives, drive covers need to be installed over the drive. Inspect pulleys and drive belts on a regular basis for proper installation and operation, along with wearing and cracking of the belt. Because some belts spin at a high linear velocity, they may pose a threat if they jump the pulleys or break, whereupon they become a high velocity projectile capable of inflicting eye or face injuries. Check cast pulleys for cracks, and check all pulleys for tightness on the shaft. Properly installed and checked regularly, pulley belt systems provide the best balance of simplicity, freedom from vibration, and cost effectiveness of any drive strategy.