What is a Step Pulley?
A step pulley is a system of pulleys made up of many different sizes. The typical step pulley consists of a two- to four-pulley configuration. This type of step pulley is found on equipment such as a drill press where different operational speeds can be produced simply by changing the belt to a different pulley size. The step pulley is always operated in pairs, and when the belt is changed on one pulley, it is also changed on the corresponding pulley on the other side of the belt.
Most step pulley assemblies are cast from liquid materials; some of the very high-end pulleys, however, are forged from solid billet material such as aluminum or steel. The billet step pulley is much more true when spinning than a cast version; there is a great cost difference between the two, however, with the billet costing much more. Some designs utilize separate and independent pulleys to make up the arrangement, although this is not a true step pulley.
While most of the step assemblies are configured for V-belt use, there are also some step pulleys which utilize flat belts. This type of step system can be switched or changed on the fly and is found in lathe transmissions or some milling machines. The flat belt pulleys are typically always forged from billet stock and operate much more smoothly than the V-belt design. The V-belt type of pulley is favored in higher torque applications, though, due to the ability of a V-belt to grip the pulley with more strength.
When it has been determined that the speed should be regulated on a particular step pulley equipped machine, the process of adjusting the speed is usually an easy one. With the motor in the off position, open the belt cover. Take note of where the belt is currently positioned on the pulleys. Remember, a large pulley driving a smaller pulley will result in more power but less speed output. Conversely, a small pulley driving a large pulley will have more speed output but less power.
Once the proper pulley system has been determined for the desired outcome, the belt cover can be closed and the machine once again turned on. Now the machine can be operated at the proper speed for the desired effect. Sanding projects, for example are typically conducted at a faster speed than a cutting or shaping project. On a typical wood lathe project, the pulleys may be changed several different times.
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