What rpm motor for 2×72 belt grinder?

2 mins read
Worker cutting metal with grinder. Sparks while grinding iron.
Worker cutting metal with grinder. Sparks while grinding iron. Source: Depositphotos



Precision and performance are our goals, and we have a background in high tolerance CNC machining. Before entering the 2×72 belt grinders market, we conducted extensive study into what makes a good belt grinder and what qualities are most necessary in a good knife grinder. The engine is by far the most significant component of the grinder.

It doesn’t matter how good the frame is if there isn’t enough power to keep a belt going smoothly and without lag. It doesn’t matter how precise your tracking & drive wheels are if the motor doesn’t have sturdy bearings as well as an accurate drive shaft.

As a result, one of the very first things that we did was purchase a variety of 2HP electric engines, both imported and local, single & three phase, or put them through its paces to determine the best possibilities.

When our initial launch is complete because we have some time, we will publish the testing results, but in the meanwhile, our key conclusion is to buy American, preferably Leeson, Baldor, and Marathon.

Motors are electric.

The motors we sell are two-horsepower 1725/1800 rpm three-phase 56c face mount four-pole electric motors that employ variable frequency drives (VFDs) to convert from single-phase 110v or 220v electricity to the three-phase power required by the motor.

Simultaneously, the VFD provides smooth and precise variable speed control. Despite their lower rpm, we chose these 4 pole motors since we can double its speed by changing the hertz between 60 to 120 with both the VFD and keep full power up to the motor’s initial 1800 rpm with a gradual drop off as it rises to 3600 rpm. However, when you accelerate, you accumulate momentum inside the form of rotating momentum, which helps to compensate for the torque loss. Compared to something like a Two pole 3600 rpm motor, which loses torque over the whole rpm range instead of just half of it.

Two-pole vs. four-pole

Standard AC motors feature two poles, or two electromagnets on opposite ends of the motor, which everyone is familiar with. One pole is north another is south at any one time whereas the motor is running.

  • The fluctuating magnetism allows the engine to spin by switching the polarities back and forth.
  • In a continual tug-of-war, the fields are swapped twice every rotation, always seeking to repel one close end of the motor’s armature while attracting the opposing side.
  • A four-pole motor has double as many permanent magnets, with one every 90 degrees rather than 180 degrees.

The very same basic principles apply, except the magnetic field is shifted four times every rotation instead of twice. It’s like playing tug-of-war with four rope ends rather than two. More the poles a motor has, the greater torque it produces, just as a four-cylinder engine against a V-8.

Drive with Variable Frequency

A vfd drive (VFD) modifies the frequency of a AC current motor speed using electronics. Because the frequencies of the Ac power delivered is directly related to the motor’s speed, adjusting the frequencies is the ideal route to vary the motor’s speed. Because standard household electricity is 60 Hz, increasing the speed to 120 Hz will double the motor’s speed, while decreasing its frequency may decrease the motor’s speed.

Considerations for Speed/Torque

The output frequency of most AC drives is 120 Hz or higher. The output voltage, however, is restricted to the voltage level. A drive powered by 220 v can only output 220 volts. As a result, as the frequency rises over 60 Hz, the voltage output remains constant while the volts per mhz ratio falls, resulting in torque loss, albeit at only the highest speeds.

By using a four-pole 1725/ 1800 rpm motor, you can maintain full torque in the vital low-speed zone, when the extra power is most needed.

When compared to a 2 pole 3600 rpm motor, the maximum torque is only available around the rated wind speed of 3600 rpm. When the speed of a two-pole motor is reduced, the torque is reduced as well. As a result, at lesser speeds, you have the lowest amount of electricity and are more likely to experience belt lag.

As a result, we believe that full torque inside the lower engine speed range is the most critical criterion, and given the possibilities, a Four pole 1800 RPM motors is a win-win!

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