How to fix a CNC DC Motor

Fixing a CNC DC Motor

The Direct Current (DC) motor on a CNC machine runs the whole show. When the DC motor(s) malfunction(s), the electrical systems throughout the machine can be affected negatively. In many situations, a CNC machine will operate more than one DC motor and so care must be taken when deciding if a motor’s functionality is acceptable or not. Given the environment and conditions that CNC machines operate in, DC motor failures can occur if regular maintenance and service aren’t performed consistently.

What does a DC motor do?

The Direct Current (DC) motor, also known as a Brushless DC Motor (BLDC), controls piece and tool movements while the cutting process takes place. These motors are controlled by computer programs with precision and accuracy the goal for operating performance. Turning and movement of the workpiece, tools, and other functions like fluid pump operation, are controlled using DC motors. If the movement is off by even a small fraction, damage can quickly occur to the workpiece, the tool, and the CNC machine.

Causes for DC motor damage

The operating environments for most CNC machines can be the source of many problems with DC motor functionality. The engineering of the DC motor itself can also be a factor as age and use take their toll on the device’s performance. Like with all motors and mechanical devices, time and use can produce wear and tear. Motors are susceptible to damage due to misuse, overuse, lack of proper maintenance, debris, liquids, and a host of other factors. For these reasons, it is vital to maintain all the DC motor assemblies according to the manufacturer’s instructions and perform regular maintenance and service protocols to determine functionality and productivity.

What to look for

All motors suffer from common maladies due to their basic design, engineering, and function. Depending upon where and how the motor was made, the longevity and productivity of the motor will also be affected by the environment it operates in and the amount of stress placed upon the motor during production. There are some components in DC motors that fail routinely and should be examined before continued operation without repair or replacement:

  • Bearings – all electrical motors use a “bearing” to allow the motor spindle to spin. Bearings are in constant use and over time the bearing’s surfaces will wear and degrade.
  • Windings – the electrical wires wrapped around the core of the motor are called the “windings”. Usually made from copper, the windings can become brittle and deteriorate over time causing cracks and breaks. When this occurs, the power output of the motor is affected causing problems further downstream.
  • Casings – the metal body a motor is enclosed within can become pitted on the interior causing electrical sparks or shorts. The casing can also crack due to vibration and overheating resulting in the misalignment of the winding stem which will shut the motor down.
  • Cabling – input and output electrical lines can wear against sharp or hard surfaces they encounter causing electrical shorts or power arcing across lines.
  • Balance – like all things, a DC motor must achieve balance or it will not function well for long. If a motor is incorrectly mounted inside a CNC machine and not secure, it can quickly go out of balance and fail.


Follow the leader!

Troubleshooting electrical issues can be a complex and complicated process when a CNC machine is involved. The manufacturer’s service and maintenance recommendations should be followed diligently with additional attention paid to routine inspections and preventative maintenance protocols added. The manufacturer’s service technicians can be a great source of information and establishing a relationship with the local dealership will pay dividends in the end. Logical, common sense inspection and service procedures combined with diligent attention to machine performance will help avoid costly failures and downtime.

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