They are not ideal if you use a CNC machine router. They are not designed for heavy use and require more maintenance than a spindle motor.
A generic 2.2kW router motor’s power is at its highest point when used at the lowest speed-rated by the manufacturer.
1. RPM
The rate at which a CNC router spindle motor rotates is measured in revolutions per minute (rpm). This number is crucial because it determines the rate at which your machine cuts. The higher the rpm, the faster your machine can cut. However, too much rpm can cause the motor to overheat and burn out.
The optimum feed rate for a given material depends upon many factors, including the power and rigidity of your CNC machine’s frame, part hold-down system, spindle horsepower, cutter design, sharpness and depth of cut, etc. Fortunately, some online calculators can help you determine the correct speeds and feeds for a particular material. Alternatively, consult the manufacturer’s reference manual for your router to find recommended cutting rates.
It’s important to note that a high-speed spindle’s rpm should be maintained with first running a break-in period. This process involves reducing the spindle speed to its lowest setting and increasing it incrementally until the tool achieves an acceptable edge finish. Then, the speed can be gradually increased to the maximum operating rpm.
It’s also essential that your pneumatic CNC spindles are well-balanced before use. The vibration forces imposed on a poorly balanced spindle can cause poor surface finish and rapid tool wear. You can use a balancing kit available from most CNC tool manufacturers to ensure that your CNC machine’s spindle is appropriately balanced.
2. Torque
Torque is the force a spindle motor can apply to the cutting tool. It is determined by the force of the tool times its speed, which is given by formula_2 (speed)/formula_3 (force). Torque is measured in Newton meters per second or watts. The torque and power characteristics of a spindle motor vary with the spindle’s speed, which is given by formula_4.
Most commercial CNC routers use integral motor spindles because they offer high speeds and enough torque to perform many tasks. However, the high-speed performance of an integral-motor spindle says little about its capabilities at low speeds.
Specifying the torque of a spindle motor is more valuable than specifying its speed because it can be used to determine how the machine will perform in various applications. For example, if you plan to use small cutters in soft materials, high-speed performance may be necessary, but a lot of torque will not be needed.
On the other hand, if you plan to use large cutters and high feed rates on hard materials, then a lot of torque will be required at low speeds. The type of material you are cutting will also dictate the optimal feed rate. The recommended rates in your CNC’s manual should be consulted for exact information.
3. Power
Power is a significant consideration when selecting a router spindle motor. It is more important than the speed rating of the motor. This is because the low-speed torque requirement determines the motor size needed for the application, not the speed rating.
The power needed to cut aluminum is much higher than wood, so a more powerful motor is required. This is why it is essential to understand each motor’s torque and power limitations before choosing one for a specific application.
Another important factor when determining power is the temperature that the motor can tolerate. A high ambient temperature causes the motor to dissipate heat quickly, which shortens its life and can lead to a loss of accuracy due to thermal expansion of the internal components. This is why it is crucial to properly design your machine to allow the spindle to cool efficiently. This includes proper airflow through the work area and adequate spindle lubrication. Also, using a water-cooled spindle is recommended to avoid overheating the motor.
4. Efficiency
The amount of work a spindle motor can do is measured by its power (force times velocity) in Newton meters/second or watts. The amount of power available decreases as the speed increases and is usually limited by the motor size. Spindle manufacturers often illustrate these limits with torque and power curves.
Increasing your machine’s slew rate and plunge rate can help compensate for low spindle speed, but these factors must be balanced with an appropriate feed rate to avoid damaging cutter tips. The optimum feed rate depends on the material you’re cutting and the RPM of your machine.
Some materials and tooling designs are well suited to high-rpm cutting. For example, small, ball nose end mills for hard steel mold finishing reach peak SFPM at high speeds and allow very productive feed rates. However, a 1″ 4-flute cutter cutting aluminum at 30,000 rpm requires an enormous amount of power.
Conclusion
In AC-asynchronous motors like those used in machining center spindles, the current that passes through the stator and rotor of the motor affects its magnetic lines of flux and generates torque. Technology advances have increased the maximum rated torque of these motors, but it remains a direct relationship with motor size. Water cooling can also increase a motor’s rated torque, allowing smaller motors to be used.
