CNC SPINDLE :
Brush or Brushless Motors
Most CNC router manufacturers today, give you a significant number of spindle options and then custom assemble the machine to fit your shopping list … kind of like ordering a submarine sandwich, CNC routers are often built-to-order.
So to decide what you need, first understand that spindle motors generally fall into two different categories; a basic woodworking router or a dedicated industrial spindle, motors that are often classified as either brushed or brushless.
Brush Motors:
 Brush motors as the name would suggest have brushes... there's a brilliant piece of information for you. Brushes are the carbon rods held against the commutator or central spindle of the motor, by springs. The brushes transfer power from your wall plug to the commutator to create a magnetic field that in-turn rotates your spindle head based on the laws of magnetic repulsion or force.
You can always recognize a brush type motor by the small screw-out ports on the upper shaft of the motor that allow the user to replace the brushes as needed. Motors that use brushes are usually called universal motors because they are capable of running on either a DC or AC power supply.
Advantages of Brush or Universal Motors:
- Low cost, especially when variable speed is required… as no expensive VFD (variable frequency drive) is needed. Rather in standard tools like our basic woodworking router, they use small resistors to reduce the current and thus reduce the rpm.
- Compact motor and starter/adjustable speed drive circuitry…. , keeps the weight down!
- High starting torque, which is why on a lot of the smaller hand tools they had to create the electronics for “softstart”. Remember the old routers that used to jerk out of your hands on startup?
- Capable of running at very high speeds
Disadvantages:
- Lower efficiency due to friction of brushes with the commutator…
- This friction also generates heat and reduces the duty cycle of the motor…
- These motors are not normally designed to run continuously at full capacity/load, which goes back to the comment above that the brushes on these types of CNC spindle motors, generate heat and heat buildup prevents sustained load, restricting duty cycle.
- Higher maintenance schedule compared to other types of motors.
- Lower life expectancy due to brushes and commutator wear
Brush Type motors are the mainstay of portable woodworking tools. You see them in your basic wood router, jigsaw and miter saw. They are simple and repair service is readily available at your local tool center. Having said all that there is the alternative, a Brushless Spindles Motor with its own unique challenges both good and bad.
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