When reviewing specifications for CNC motors, there are a few terms that should be known to understand the information thoroughly. Most will have a sufficient understanding of these terms to cope but it never hurts to review.
Probably the most recognizable term associated with motors is RPM or revolutions per minute. Simply enough, this term describes the rotational speed of a motor in revolutions per minute.
Torque Speed Curves
Torque describes the rotational strength of a motor. Torque is force times unit length such as oz-in., ft-lb., and N-m. When choosing a motor be sure to check the unites.
A torque-speed curve is a graphical chart representing the relation between a motors torque and RPM. This information is very helpful in judging the motors performance. Many sellers will quote a specific torque which is the maximum torque. With a torque curve you can estimate the torque at a given RPM. This is very helpful when designing your own machine as you can choose you gear ratio to get the best performance from your motor.
NEMA is an acronym for the National Electrical Manufacturers Association. Most of the time when reviewing the motor specifications, there will be a NEMA standard rating. This standard represents the motor frame size and shaft dimensions. The frame size defines the mounting face width and height and the size and position of the mounting holes. The shape and appearance may vary depending on manufacturer, even between motors with the same NEMA rating. The most common NEMA sizes for router tables are 8, 11, 14, 17, 23, 34, and 42. Lower NEMA ratings define smaller frame sizes. For more on NEMA standards such as charts, drawings, and suffixes; visit the
NEMA standards page.
The NEMA rating will give you general range of torque but has no direct relation to the motors performance. CNC motors with the same NEMA rating may have very different performance.
A motors power rating refers to the voltage rating of the motor and the current per phase. Power which is measures in watts, is equal to the voltage multiplied by the current. The higher the power rating the higher the work output of a motor. It is important to know the power rating of a motor so a proper power supply can be used.
There are many attributes that contribute to motor selection. In the following sections we will review all types of CNC motors in greater detail.
Stepper Motors vs. Servo Motors
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