A woodworking CNC router whose vacuum pods run off a vacuum pump uses little compressed air: 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, covers most workshops. Everything changes if the pods create their vacuum with venturi ejectors. They then use air continuously, and the sizing has to account for it.
This article covers that specific case. For the other uses of air in a woodworking shop, see our page on compressors for joinery workshops.
Where does the vacuum for your pods come from?
Ask this first, because it decides the size of the compressor.
- Vacuum pump. Most woodworking CNC routers with pods or a vacuum table have an electric vacuum pump. It holds the part without drawing on the air network. Compressed air then only drives the machine functions.
- Venturi vacuum generators. Some machines, or pods added later, create vacuum by passing compressed air through an ejector. Each ejector uses air for as long as it holds the part, so throughout the whole cut.
The machine manual says which, in the pneumatic supply section. If an ejector is fitted to the table, its label or data sheet gives its air use in l/min.
What uses air on a woodworking CNC
Even with a vacuum pump, the machine uses air for:
- tool changes and releasing the spindle taper, in short bursts;
- cylinders: pop-up stops, positioning or locking the pods, hold-downs, the dust hood;
- blow-off of the table and the part at the end of the cycle, which uses a lot when it is programmed;
- spindle air, on spindles that need it, low but continuous. Our article on spindle air purge covers the air quality required.
The calculation, step by step
Take a CNC router with pods whose manual gives 150 l/min in normal use, at 6 bar minimum. This figure is an example: replace it with your own machine's.
Case 1, vacuum from a pump.
- Machine: 150 l/min.
- Operator's blow gun: 150 l/min as a guide while it blows. It works in bursts, so our configurator counts it at half, 75 l/min.
- Subtotal: 225 l/min.
- 25 % safety margin: 225 × 1.25 = 281 l/min.
- 20 % margin for growth: 281 × 1.2 = about 340 l/min.
Case 2, four venturi ejectors. Assume 60 l/min per ejector from its data sheet, all active while cutting.
- Ejectors: 4 × 60 = 240 l/min, counted at 100 % because they blow continuously.
- Machine and blow gun: 225 l/min, as in case 1.
- Subtotal: 465 l/min.
- With both margins: 465 × 1.25 × 1.2 = about 700 l/min.
The requirement doubles with ejectors, on the very same machine.
Which compressor for your workshop?
| Situation | Calculated need | Recommended model |
|---|---|---|
| One CNC, vacuum pump, few other tools | about 340 l/min | S 55 (0.6 m³/min at 8 bar) with an air receiver and dryer |
| One CNC with ejectors, or a CNC plus assembly benches | about 700 l/min | K 75 (1.1 m³/min at 8 bar, 420 L receiver) |
| CNC, edge bander and finishing on the same network | over 1,000 l/min | K 110 (1.7 m³/min at 8 bar) |
The S 55 comes without a receiver or dryer: it suits a shop that already has its air treatment. A 4-in-1 is simpler when you start from scratch, because dry, filtered air comes out of a single frame.
Pitfalls specific to woodworking CNCs
- Pressure during the tool change. The machine often monitors its inlet pressure and stops on a fault if it drops below the minimum. Read the pressure on the machine gauge during a tool change, not at rest. If it drops, check the pipe size and the fittings first: see our guide to connecting to the air network.
- Water in the valves. Wet air makes solenoid valves stick and rusts cylinder rods. A dryer is not a luxury, even if the machine does no finishing.
- Wood dust. The compressor draws in workshop air. Place it away from the machine and the extraction, and check its intake filter often.
- Forgotten blow-off. A programmed table blow-off that runs too long weighs more than everything else. Our article on chip blow-off shows how to measure and cut it.
For a first figure, enter your equipment in the configurator. Then send us your CNC manual with a quote request: we will check the flow and pressure with you.
For your trade: Compressor for joinery workshops.