When choosing a spindle for your CNC or micro-CNC machine, you need to consider what operating speeds and torque you need from the spindle. Both of these factors will directly affect the type of work that the spindle can handle and its own performance.
A pneumatic spindle is one that operates using compressed air. They have advantages over electric spindle in terms of cost, weight and noise production. Pneumatically driven spindles also provide a more stable torque output with less vibration than an electric equivalent would.
Consequently, pneumatic spindles are ideal for smaller machines where noise needs to be kept to a minimum and cost is a key factor in the purchase decision. Let’s take a look at how they work, their pros and cons, and some examples in use today…
Pneumatic spindle operation
A pneumatic spindle will use a motor to drive the spindle head. This motor will be connected to a rotary vane air compressor, which will then feed compressed input air to the spindle (there are even water cooled spindle with er11). A pressure regulator at the input of the compressor will control the pressure of the compressed air, allowing for a wide range of possible spindle speeds.
Higher pressure will result in a higher spindle speed, but also a higher torque, while lower pressure will have the opposite effect. The compressed air then passes through either a rotary vane or piston air pump. This pump will feed the air to a spindle valve, which is then sent to the spindle head via a spindle feed tube.
The spindle feed tube will then be connected to the spindle’s collet, or directly to a spindle nose.
Pneumatic spindle benefits
– Cost. Pneumatic spindles are cheaper than electric spindles. This is as they don’t require any additional power supply and also weigh less, which can be important in some applications.
– Weight. Pneumatic spindles are also lighter than most electric spindles, especially in larger sizes. This is important for smaller and lighter machines, helping to keep the overall weight down.
– Noise. Pneumatic spindles are generally quieter than electric spindles. This is especially true for larger spindles where there is more vibration.
– Torque stability. Pneumatic spindles also offer a more stable torque output than electric spindles due to their lack of start-up inertia.
Pneumatic spindle limitations
– Torque. Pneumatic spindles cannot generate as much torque as electric spindles. This is true even in larger sizes, but is especially significant at lower spindle speeds where the difference is more noticeable. Consequently, they are not suitable for heavy work.
– Speed. Pneumatic spindles can only operate up to a certain speed. This is due to the design of the air compressor. Beyond this point, the compressor will not be able to keep up with the demand for more compressed air, resulting in a drop in spindle speed.
– Heat. Pneumatic spindles also run the risk of overheating due to their use of compressed air as a drive source. This is true especially in larger spindle sizes and at higher spindle speeds.
What to look for in a pneumatic spindle
– Spindle speed. The first thing to look for in a pneumatic spindle is its maximum spindle speed. This will help you to determine what type of work the spindle can be used for.
– Spindle torque. The second thing to consider is the spindle’s torque. This will help you to determine the spindle’s capacity for heavier work.
– Spindle type. There are two main types of pneumatic spindles: direct drive and belt drive. Direct drive spindles have the spindle head connected directly to the motor.
– Spindle mount. Finally, you will have to decide on the spindle mount type. Rotary vane spindles are typically mounted vertically while piston spindles can be mounted both vertically and horizontally.
Festo Pneumatic Spindles
One of the leading pneumatic spindle manufacturers is German brand Festo. They have a wide range of air-powered spindles for a wide range of applications. One example is the FEO30/2.2-D, which is a direct drive, 30 mm diameter spindle suitable for heavy-duty CNC applications. It can handle up to 1.2 Nm of torque at speeds of up to 8,500 rpm.
The FEO30/2.2 is a vertical spindle that has a maximum recommended workpiece weight of 25 kg. It has an air consumption of 7.5 l/min at a pressure of 0.5 MPa. Another pneumatic spindle from Festo is the FEO45/2.2-D, which is a direct drive, 45 mm diameter spindle suited for light-duty CNC applications. It can handle up to 1.2 Nm of torque at speeds of up to 6,500 rpm.
The FEO45/2.2 is a vertical spindle with a maximum recommended workpiece weight of 25 kg. It has an air consumption of 8.6 l/min at a pressure of 0.5 MPa.
Epiroc Pneumatic Spindles
Swedish brand Epiroc also offers a range of pneumatic spindles for varying applications and machines. Their most powerful pneumatic spindle is the E-torq P9/3-D. This is a direct drive, 9 mm diameter spindle suitable for heavy-duty CNC applications such as drilling, milling and bar-cutting.
It can handle up to 12 Nm of torque at speeds of up to 7,000 rpm. The E-torq P9/3 is a vertical spindle that has a maximum recommended workpiece weight of 3 kg. It has an air consumption of 6 l/min at a pressure of 0.6 MPa.
Pneumatic spindles are the best choice for smaller machines and lighter work where noise needs to be kept to a minimum. They offer a cheaper and lighter solution than electric spindles and are more stable in terms of torque output.
These spindles are best suited for smaller machines, as they can’t handle heavy work. They are also limited in terms of maximum spindle speed, so you will have to choose a spindle that is suitable for the type of work you intend to do.