Human error has been the sworn nemesis of progress in the field of precision tasks. As attention to detail has evolved to a non-negotiable demand for detail, the minute variations and vacillations in human-operated machinery have become unacceptable. For this level of manufacturing, human-aided automation has been a boon to achieving the necessary precision. Computer numerical control, or CNC, is an automation process that uses a coded program to perform high-precision tasks involving tools such as drills, lathes, grinders, and even torches or jets. Most modern embroidery is done not by hand but by CNC, and the 3-D printers that are changing today’s world rely on the latest in CNC technology.
CNC operates along three axes: the horizontal x and vertical y-axes as well as a third, the z-axis, which introduces the third dimension into the process. The key to CNC technology is the spindle, which moves up and down along the z-axis to punch, drill, and cut the material as movement along the x and y-axes brings it into place. This spindle, standing in for the human touch, requires amazing precision. What lends it this precision is a specific type of electromagnetic motor—one that moves in discrete but rapid increments, with variable speeds and the ability to start and stop quickly. Spindle motors have been indeed been a boon to manufacturing processes, but there are multiple motors for varying jobs. Consult this guide to choose a spindle motor for your application and learn what to do should a spindle motor fail.
Spindles typically run on one of two similar models of motor. Older, simpler, or less powerful CNC tools use stepper motors, which get their name from the increments, or steps, they operate in. Stepper motors are either built around permanent magnets in their rotors that are drawn to their housings, or use magnetized housings to attract the rotor. In the latter model, known as a variable-reluctance stepper motor, the spindle can achieve higher speeds than it could with a permanent magnet in the rotor. Stepper motors are the less popular and less powerful of the two motors most common to spindles. If you’re a CNC hobbyist or small business owner, you may be able to get away with a stepper motor for your spindle. While stepper motors are sufficient for basic CNC applications, steppers lose torque at high speeds, meaning tasks requiring more power or precision call for another approach.
The servo motor is the sophisticated older brother of the stepper motor. Though servos, like steppers, are electromagnetic motors with magnetized rotors or housing, servo motors have lower pole counts within their motors than steppers. Perhaps the most important distinction between stepper motors and servo motors is the communication loop. Stepper motors use an open communication loop, meaning that they receive their signals purely from voltage. Servo motors, on the other hand, use closed-loop communication, meaning they send and receive signals from a controller. Servo motors work in conjunction with gearboxes to maintain high torque at high speeds, and when vacillations in torque occur, servo motors can compensate for these shifts. With higher speed, higher acceleration, and higher accuracy, servo motors are the spindle motor of choice for most CNC applications. Of course, a higher cost attends all these benefits as well. With many more moving parts than a stepper motor, a servo motor and its corresponding gearbox are more prone to failure.
Beyond this division, spindle motors come at different maximum speeds. Just like your car’s engine, we measure the speed of a spindle in revolutions per minute, or RPM. The material you’re cutting or drilling and the detail that the job requires determine the necessary speed of your spindle motor. Generally, the smaller the details you’re working with and the smaller the surface you’re working on, the higher you’ll need your spindle speed to be. Micro-tooling, a variant of CNC most often employed for tasks such as engraving, uses low-diameter tools and high speeds, sometimes as high as 60,000 RPM. Most industrial spindles have maximum speeds that range from 12,000 RPM to 40,000 RPM.
Spindle speed is important, but speed is nothing without torque behind it. Torque is the rotational force that forms the key principle behind spindle motors. Torque is based on force, radius, and angle, but as a spindle’s speed increases, its torque naturally declines. Larger motors are capable of producing higher torque at the expense of a more cumbersome spindle less suited to maximum-precision jobs. It’s a difficult balancing act, and one which engineers have set out to achieve by redesigning spindle motors to provide torque while getting out of the way. One such instance is the overhanging motor, where cantilevering the motor to the back can make more room for the tool to work. The harder the substance you’re working with, the more torque you’ll need. While low torque is sufficient to cut most woods, you’ll need high torque in order to cut steel.
Basic day-to-day maintenance of a spindle motor is necessary to keep it in fine working order and prevent overheating or breakdown. Additionally, you should not only take care of your spindle motor, but you should also be very conscious not to overload it. The capabilities of CNC technology are impressive, but you should still always avoid giving your spindle more work than it can handle. Owing to the high speeds and torque that CNC machinery employs, spindle motors can fail. If they do, Moley Magnetics has you covered. Our electric motor repair services handle numerous varieties of electromagnetic motors, from stepper motors to servo motors, inside or outside the CNC field. Gearboxes, which are integral to the operation of servo motors, are also prone to failure after regular wear and tear. If this should happen to you, Moley Magnetics can open the box and perform the necessary repairs as well. To repair a failing spindle motor and get your CNC manufacturing processes back on track, no matter how you choose a spindle motor for your application, keep Moley in mind.