As spindle plays the most fundamental role in any CNC machining applications, you should choose the right milling head for your device. However, the selection should be based on your experience level and purpose. For example, if you are a DIY CNC mill user, then going for a brush spindle with a plastic housing is sufficient to cut soft fiber, plastics or plywood. But, if you are a pro-grade CNC machinist whose services will ultimately bring in the money home, then the above choice is not suitable.
The plastic housing spindle cannot stand more than a few hours in hard-core industrial applications. Plus, for economical works, such spindles will scarcely last for 6 months.
For professional CNC applications, you need to choose the pro-grade brushless inductive inverted-oriented spindles having durable ceramic bearings and features a compact engine compartment within a metal-housing.
While selecting your desired spindle, notice the product’s identification where you will find the nominal speed value of the spindle is given as (12000, 15000, 18000, 24000, 40000) RPM (Revolutions Per Minute). But mind you that the spindle does not always spin within these limits. You can control the spindle’s RPM by that inductive inverter. However, you also have to remember that the power of the spindle is the torque value multiplied by the speed of rotation. So, when you preserve torque and decrease the RPM by half, the power also drops by half.
You see, there is no one-stop spindle option you can use for any type of CNC applications. If you want an industrial spindle, then a high-power spindle with larger diameter bearings is an ideal fit. Just be careful with the material used in the bearings. Better the bearing material used in its making, longer is the spindle-life and more optimal is the speed limitation of the spindle.
However, larger bearing diameter means greater centrifugal force of the balls that press on the bearing’ outer ring’s running track. This results in more heat release which has the capacity to decrease the tool life. So, one of the feasible ways to decrease this heating effect is to use lighter balls made of ceramics. That is why spindles with a speed limit of 40.000 RPM are generally produced in low-power ranges only.
Conversely, the high speed of the spindle is perfect for achieving materials including wood, laminates, aluminum, composite materials, and more. However, while machining stainless steel, thermoplastics or drilling with HSS(High Speed Steel) drill bits, high speed is not so applicable.
Talking about the power, here are the two main criteria:
(i) the maximum diameter of the CNC machine cutter to be used and
(ii) type of materials machined using these milling cutters.
For instance, to process plastic, wood, aluminum, or laminates with milling cutters of up to 5 millimeter, the spindle with (0.8kW 24,000 RPM) specification is workable, while for cutting tools sizing up to:
- 8 millimeter – 1 kiloWatt spindle,
- 12 millimetre – 3.3 kiloWatt spindle, and
- 16 millimetre – 5.6 kiloWatt spindle, are sufficient.
To process steel materials, it is better to opt for a spindle with lower RPM range, i.e. from (15,000 to 18,000) RPM. Accordingly, for the cutting tools sizing up to:
- 12 millimeter – 5.6 kiloWatt spindle,
- 16 millimeter – 7 kiloWatt spindle, and
- 20 millimeter – 10kiloWatt spindle, are highly recommended.
Conclusively, if you are looking for a spindle for drilling steel, always go for the high-power speed. For example, to drill with a 6 millimeter drill bit in steel material at 2200 RPM with 5.6 kilowatt and 18,000 RPM spindle, only 0.6 kiloWatt is sufficient. You can’t differentiate between the spindle powers and conventional powers of milling machines as they come with gears and have no need of reserve torque. One more point is that such types of spindles have a longevity of around 10 years.