Two different forms of rotation speed control are fundamentally used with sliding table saws and spindle moulders.
The power is transferred from the motor to the tool shaft by belts. Multiple belt pulleys with a range of different diameters sit on top of each other on the motor and on the tool shaft. A higher or lower speed is attained, depending on the pulley combination over which the belt runs. The belt position is determined by a mechanical or electronic sensor, and displayed on the front of the machine in the form of a mechanical or electronic rotational speed display.
The electronic control of the rotational speed of three-phase current motors can take place according to two different technical principles:
- With motors with switchable motor windings it is possible to increase or reduce the speed with a switch. Disadvantage: As with rotational speed change through a change in the belt pulley combination, the torque reduces with an increase in speed. In the past, this principle was usually used in combination with various belt pulleys. Since the introduction of the frequency converter, the application of this principle has declined significantly.
- The speed is controlled by a change in the three-phase current frequency, with the aid of a frequency converter. Advantage: The torque remains constant over a broad rotational speed range. This form of rotational speed control is seen in machines in the form of displays with buttons or trim switches.
- Large tools must not be operated at high rotational speeds. Small tools produce better results with high speeds.
- Profile sanding tools have their optimum efficiency/service life in the lower rotational speed ranges.
- Plastics are processed at a lower rotational tool speeds than wood, in order to avoid a smudging of the plastic.
The average maximum speed with spindle moulders is 10,000 rpm.