Four machining centres usually need between 0.3 and 0.9 m³/min at 7 to 8 bar, depending on how much programmed blow-off they use. In most shops, a 7.5 kW 4-in-1 screw compressor such as the K 75, which delivers 1.1 m³/min at 8 bar with a built-in dryer and filtration, supplies all four machines. Move up to the K 110 when the machines blow off a lot or the shop runs several shifts.
What does a machining centre consume?
A machining centre uses air for several functions, and they do not consume in the same way:
- in short bursts: the tool changer and drawbar release, pneumatic fixtures and vices, the automatic door;
- continuously, but little: the spindle air purge;
- continuously, and a lot: programmed blow-off of parts and chips.
As a rough guide, a machining centre uses about 50 to 150 l/min on average. The figure that counts is in the manual, under the pneumatic supply section, together with the minimum inlet pressure. Our page on the compressor for CNC machining covers every use of air in a machine shop. Here we look at one specific case: four centres.
Step-by-step sizing for four centres
Take a typical shop: two 3-axis centres without programmed blow-off, at 60 l/min each according to their manuals, two 5-axis centres that blow the part clean at the end of each cycle, at 140 l/min each, and one operator cleaning parts with a blow gun.
- The machines: 2 × 60 + 2 × 140 = 400 l/min.
- The blow gun: about 150 l/min while blowing. It is used in bursts and the air receiver smooths those peaks, so count it at half: 75 l/min.
- Subtotal: 400 + 75 = 475 l/min.
- 25% safety margin for leaks and wear: 475 × 1.25 = 594 l/min.
- 20% expansion margin for a fifth centre: 594 × 1.2 = 713 l/min, or about 0.71 m³/min.
These are the margins our configurator applies. You add up average consumptions, not peaks: four tool changes rarely happen in the same second, and the air receiver absorbs these short demands. The air receiver size calculator checks that the volume is enough.
What pressure should you set for four machines?
Read the minimum inlet pressure in all four manuals, often around 6 bar, and keep the highest. Add the losses across the dryer, filters and pipework: a setting of 7 to 8 bar suits the vast majority of shops. Check the pressure on the gauge of the furthest machine during a tool change, not when everything is idle.
If one machine asks for more, the K 75 comes in a 10 bar version: it then delivers 0.95 m³/min, which still covers the 713 l/min of the example.
Which model for four machining centres?
| Situation | Recommended model | Flow |
|---|---|---|
| Four centres, moderate blow-off (example above) | K 75, 7.5 kW 4-in-1 screw | 1.1 m³/min at 8 bar, 420 L receiver |
| Four centres with heavy blow-off, or two to three shifts | K 110, 11 kW 4-in-1 screw | 1.7 m³/min at 8 bar |
| Receiver and dryer already installed | S 75, 7.5 kW standalone screw | 1.1 m³/min at 8 bar |
With four machines, demand changes all the time: one cycle is blowing, another is changing tools, a third is stopped for setting. The S and K series are variable speed and follow that demand. See variable speed or fixed speed.
Pitfalls in a four-centre shop
- Forgotten blow-off. A programmed nozzle left open for the whole machining cycle can use as much as two machines. Check in the program when blow-off opens and closes before buying a bigger compressor.
- Leaks times four. Four machines mean dozens of fittings, solenoid valves and hoses. Our article on compressed air leaks explains how to find them.
- Undersized pipework. A pipe that is too small drops the pressure at the end of the line, on the fourth machine. A ring main around the shop balances the pressure. See a leak-free compressed air network.
- Water in the valves. It makes the tool changer stick. The K 75 dries the air as standard. A fine filter at each machine completes the protection.
Send us the list of your four centres and their manuals with a quote request: we will check flow and pressure with you.
For your trade: Compressor for CNC machining and machining centres.