Most machines accept a difference of a few rpm, so the first step is to calculate the speed given by the nearest standard ratio. If the difference is not acceptable, the options are:

  • Changing the motor's number of poles: 6 poles instead of 4 gives roughly one third lower speed with the same ratio.
  • An extra stage: adding a belt and pulley or chain and sprocket after the gearbox; the diameter ratio divides the speed a second time.
  • Another series: according to the tables on the product pages, the M-HEM and HF ratio range runs from about 3.5 to 290 depending on frame size, with intermediate values closer together than the steps of the worm series.
  • Frequency inverter: the most flexible route when speed must be adjusted continuously; however, motor cooling and torque at low frequency are assessed separately.

Details of inverter operation are covered in the motor with inverter questions guide. The exact ratio list of the chosen frame is confirmed in the catalogue and quotation.