Gear And Pulley Speeds
| When building or modifying machinery it is necessary to calculate the size of gears or pulleys required to run a tool at a certain speed. Sometimes it is relatively simple, if you are replacing a 3450 RPM motor with a 1725 RPM one usually all you have to do is double the size of the pulley on the motor to run the machine at the same speed.
Going the other way, replacing a 1725 RPM motor with a 3450 RPM motor may not be so simple if the driving pulley on the motor is already a small diameter. The required pulley would be too small to be practical so the driven pulley would have to be replaced, however if this pulley is already fairly large, doubling the size of it would again be impractical. To get around this the pulley on the motor will have to be somewhat smaller and the pulley on the machine will have to be somewhat larger, this can be calculated using a formula. Gear Speeds & Sizes Speed of Driven Gear = Teeth on driving gear multiplied by RPM of driving gear divided by teeth on driven gear. Teeth of Driven Or Driving Gear = Teeth on gear multiplied by its RPM divided by RPM required. Speed of Last Driven Gear Divide product of driving gear sizes (number of teeth) by product of driven gear sizes and multiply quotient by RPM of first driving gear, this equals speed of last driven gear.
Ratios of Gear Drives A gear ratio indicates the speed relationship between driving and driven gears. For example if a driving gear has 15 teeth and the driven gear has 45 teeth the ratio is 45 divided by 15 which equals 3 giving a ratio of 3 to 1. Pulley Speeds and Sizes Size of Driven or Driving Pulley = Diameter of pulley multiplied by its RPM divided by RPM required. Speed of Last Driven Pulley Divide product of driving pulley diameters by product of driven pulley diameters and multiply quotient br RPM of first driving pulley, this equals speed of last driven pulley.
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