Are you investing in the promise of computer numerical control machining? You'll need motors to power that mill. We'll help you decide which kind to use.
Two words sum up the work you do when assembling or maintaining a CNC mill: decisions, decisions. Do you want to splurge on a servo motor, or are you content to settle for a stepper? Do you want your cutting tool to work along three axes or five? Another question for that spindle motor: do you want a brushed motor or a brushless one?
If you're not familiar with what goes on inside a DC motor, you may not be familiar with the brushes. These are extensions on the rotor—usually made of carbon—that conduct an electrical current. However, some DC motors manage to do without. Whether you should get a brushed or brushless motor for your CNC mill depends largely on your usage patterns and your budget.
How Do DC Motors Work Without Brushes?
DC motors are among the many types of electric motors. In a traditional brushed DC motor, the internal rotor is an electromagnet, while the external stator is a permanent magnet. The brushes reverse the electromagnetic field and allow for full rotation. The innovation of the brushless motor is that it inverts the structure: the outside is electromagnetic, while the inside is permanently magnetic. This removes the need for brushes to conduct the current.
Wear and Tear
Wherever there's movement and friction, there's wear. Anyone who has ever written something down with a pencil knows that graphite wears down. That's why we have pencil sharpeners, after all. The graphite in DC motor brushes can wear down as well, eventually nullifying the motor. If you plan to run your CNC mill in heavy rotation, you may find yourself burning through brushed motors.
Brushless Motors: High Expenses
It would seem, then, that the best plan of attack in putting together a CNC mill is to rely on brushless motors to power the spindle. Brushless motors are indeed longer lasting than their brushed counterparts. They're also slightly more energy efficient, and they generate less noise. However, you should be prepared to pay a premium for these benefits. Brushless DC motors can be significantly more expensive than brushed iterations thanks to both the higher technological sophistication and the sheer cost of additional copper.
The Final Decision
With these factors in mind, it's how much machining you plan to do that guides whether you should get a brushed or brushless motor for your CNC mill. If you're strictly a hobbyist who plans to do some cutting on the weekends, you're better off with brushed motor. If this is part of a burgeoning professional operation, spare no expense and opt for brushless motors.