What Size Stepper Motor is Best for a CNC Router?

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Deciding which is the ideal size of the stepper motor for the CNC router is often very confusing, and the more you do research, the more overwhelmed you might become. Moreover, due to the high number of CNC routers as well as stepper motors on the market, making an informed decision is even more complicated than before.

Fortunately, you never have to undergo this frustrating experience ever again, as in this article, you will be taken through the various factors that you need to consider to help you make a knowledgeable decision. This applies whether you are on a tight budget or willing to spend big, so read through and get enlightened on the factors you need to consider when looking for the perfect stepper size for the CNC router.

Consider current and voltage needs 

When looking for a stepper motor, one of the most important things you need to consider is the current, voltage, maximum step pulse rate as well as micro-stepping. Therefore, you should also make sure the drive is capable of handling a broad range of current hence enabling you to test various voltage levels of the system that best fit your application.

Typically, the stepper driver needs to produce a minimum of 1.4 times the rated current on the motor. Consequently, select the driver which has numerous step resolutions to be able to test for different micro-stepping settings, which almost guarantee the smoothest possible motion. Furthermore, ensure the driver received an adequate amount of power necessary to rotate the stepper motor at the wanted speeds

Establish the load requirement 

At all times, you should always establish the load time between frictional and inertial load. If you want purely inertial, you should then make use of a type of transmission that matches motor torque to the load torque. Additionally, make use of a machine that measures the force needed to have the load move at the desired acceleration and speed. To help you out, you can either measure the rotary force using a torque watch or take the force’s measurement on the linear axis.

Secondly, you should also establish the use of the supply voltage. With this in mind, you will be in a better position to choose a stepper motor that incorporates at least twice much torque than is needed to achieve the targeted operating speed. Moreover, you need to make use of a stepper motor that has a rating of approximately 1/4 that of the supply voltage. After that, take a look at the required driver current that will help you achieve the desired motor torque, and consequently, use this number to choose a stepper driver

Take note of torque issues 

Most issues related to the stepper motor are usually torque-related, with the two most common incidences being inertia mismatch as well as lack of adequate torque speed.

Inertia mismatch usually causes the stepper motors not to accelerate fast enough due to an inertia mismatch between the load and motor. To solve this issue, you need to make sure the size of the motor is matched closely to that of the load size. If you overlook this, the motor will subsequently have a harder time accelerating bulky, unstable load, and this could consequently lead to the system stalling if it is accelerated very fast.

Moreover, the CNC router’s system may reverberate, hence start to produce jittery motion, loud noise, or inaccurate steps due to the lots of torque being produced by the stepper motor. If the load is not bulky enough to handle the high-torque being produced, everything gets intensified through the stepper motor’s vibration.

The second issue is also a lack of sufficient torque at speed with most stepper motors designed to perform at their best at particular speed ranges. Thus, if you use a high-speed stepper motor on a low-speed application, you most probably will be using plenty of power, which would consequently result in the motor stalling because of enough torque. The same happens when you use a low-speed motor to perform high-speed applications.

Apply the correct voltage 

Micro stepping helps increase the system’s resolution, thereby preventing noise and vibration as well as ensuring a smooth rotation. Nevertheless, an issue arises typically when you apply incorrect voltage to the chopper drive or PWM (pulse width modulation). For instance, if the motor has a rating of 5V, you then must be asking yourself why it needs bigger voltages, right?

Likewise, you might also be wondering why you never experience an enhanced performance even after you change the chopper driver or PWM. This is, however, usually because of some other fundamentals such as electrical time constants and EMF that are often overlooked by engineers when making use of drives and stepper motors. Subsequently, this leads to a stepper motor driver or motor and driver that is wrongly configured and which are deprived of power needed for various applications

Choose the correct stepper size for your CNC router 

The choice of a stepper motor that is not an appropriate size usually shows itself in several ways. When you undersize the size of the stepper motor, this results in unsatisfactory deceleration and acceleration, poor performance as well as excessive heat. Additionally, in extreme cases, the stepper motor will position improperly, lose pulses or stop working altogether when under high acceleration or deceleration, and heavy loading.

Overloading, on the other hand, causes the stepper motor to produce higher RFI/EMI as well as to run louder. Because of this, you may incur an extra cost for a driver and motor as well as more machine or panel space than is needed.

Furthermore, because this is an open-loop system, the matching of rotor-inertia to load-inertia is vital. This is especially regardless of whether an encoder is added, but the inertia mismatch can never exceed the magnitude order. Typically, a greater mismatch results in the stepper motor missing position, using excessive current, losing pulse, or in some cases stalling altogether


After going through this article, you now have an idea of what you need to consider to help you choose a stepper motor for your CNC router that is of an appropriate size. Consequently, you will get to benefit from an effectively working machine that meets all your needs.

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