A CNC machine’s spindle is simply the motor performing the actual cutting with the help of the cutting tool. The spindle can then be viewed as the actual router of a CNC cutting system. There are a number of spindle options available for the end user specific to the material being cut such as wood or metal. Correct spindle choice involves many factors, including: horse power, rotations per minute, load ratings, power requirements, collet type, and collet size.
The weight of the spindle is another important aspect to make note of. The machine needs to be able to support the weight of the spindle as some spindles can weigh upwards of 18-20 pounds. Weight should not be a compromising factor when it comes to speed and overall performance of the CNC machine. Remember that it is important to have the correct spindle in order to achieve high performance.
Types of Spindles—2 Main Categories
Brushless/AC Spindles:
- No maintenance issue of brushes wearing out
- Do not have noise associated with brush type spindles
- Better TIR (Total Indicator Runout) rating—measures how true the rotation of the shaft is
- More expensive
Brush Spindles:
- Use commutating brushes to transfer current to coils that cause shaft to spin
- Brushes wear over time and with use
- Brushes wear out more quickly under heavier applications
- Very noisy due to commutating brushes
- Lower in cost
3 Types of Brushless/AC spindle motors
1. Fixed collet spindle
- Requires collet to be changed with manual operation (using a few wrenches)
- Simple, but can take 3-5 minutes
2. Manual quick change spindle
- Electro/pneumatic system releasing current tool and replacing it with another in a matter of seconds
- Requires operator to activate a signal to release tool and activate another button to reload next tool into spindle
3. Automatic tool change spindle
- Electro/pneumatic system
- No need for operator intervention
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