A cyclone separator in CNC dust extraction separates over 95% of wood and aluminium chips from the air stream by the centrifugal principle before they reach the fine dust filter or the impeller of the side channel blower. This extends filter life by a factor of 5 to 10 and protects the side channel blower from coarse particles. The suitable size depends on the volume flow of your side channel blower: for a 4 kW side channel blower (standard on the PFE and PFJ series), a 30-litre cyclone is sufficient; for continuous operation and 5.5 kW and more, the 60-litre version is recommended.
This article explains how a cyclone separator works, shows how to size it correctly for CNC dust extraction, in which order it is connected and what to look out for with wood, MDF and aluminium. We cover the design and sizing of the side channel blower itself in detail in the article Side Channel Blower for CNC Vacuum Tables. Here we concentrate on the cyclone.
How does a cyclone separator work?
A cyclone separator works by the centrifugal principle, that is, with centrifugal force. The air laden with chips and dust is introduced tangentially from the side into a vertical cylindrical vessel, where it is set into rapid rotation. The heavier particles are pressed outwards against the cylinder wall by the centrifugal force, lose momentum there and fall into the collection container below. The cleaned air rises again in the centre of the cyclone and is drawn off by the connected side channel blower.
The decisive control variable is the peripheral speed of the air stream: the higher the peripheral speed, the stronger the centrifugal force acts and the better the separation. Longer, narrower designs tend to achieve better fine separation. Important to understand: the cyclone is a purely passive component without a motor of its own. It does not generate any suction power itself, but uses the air stream that the side channel blower supplies. The matching between the cyclone and the side channel blower therefore determines the overall performance of the extraction system.
What separation efficiency does a cyclone separator achieve?
Standard cyclones such as the BZT models achieve a separation efficiency of 95 to 99% for coarse particles and dust. According to BZT product information, a well-sized cyclone separates over 95% of chips and dust before they reach the filter, regardless of whether you use the 30-litre or the 60-litre model. The difference between the sizes lies not in the separation efficiency but in the capacity and thus in the run time, that is, how long you can work without emptying.
The last few per cent of the finest dust below 5 µm is not captured by the cyclone. This is exactly where the interplay with the downstream fine dust filter comes in, which we cover below.
Wood, MDF or Aluminium: What Matters for the Material
The separation efficiency and the requirements for the system depend heavily on the material being machined. Anyone who mainly processes wood and panel materials on their gantry milling machine has different requirements from someone who machines aluminium.
- Wood and MDF dust: very fine and with a low specific weight. The cyclone separates it well, but transporting it requires a high air velocity. For health protection, fine dust filtration is also necessary, because wood dust falls into dust classes M or H.
- Aluminium chips: larger, heavier and with a higher density. Cyclones separate over 97% here, the filter load drops significantly, and smaller units can also be used.
- Mixed operation (wood and aluminium): Choose a cyclone that is optimised for the larger chips, and size conservatively on an MDF basis, since the fine dust clogs the filter faster.
Which materials your machine can sensibly machine at all depends on the series. You will find an overview of all models and their material suitability in our Series Comparison Table and in the CNC Gantry Milling Machines category.
Sizing the Cyclone Correctly: Matching with the Side Channel Blower
The most important rule for sizing is: the cyclone separator must not throttle the volume flow of the side channel blower unduly. A cyclone that is too restrictive, with a vortex finder that is too narrow, reduces the cubic metres delivered per hour. At the same time, the cyclone inlet needs a minimum air velocity of about 15 to 18 m/s so that the chips are transported and separated reliably at all.
As a guide, use the following assignment of side channel blower power, volume flow and suitable cyclone size. The volume flow values and matching rules come from our article on the Side Channel Blower for CNC Vacuum Tables.
| Side channel blower | Volume flow (approx.) | Typical cyclone size | Target group / series |
|---|---|---|---|
| 1.1 kW | 145 m³/h | 20 L | PFI / PFK, hobby |
| 2.2 kW | 210 m³/h | 20–30 L | PF / PFA, commercial |
| 4 kW | 320 m³/h | 30 L (standard) | PFE / PFJ |
| 5.5 kW | 420 m³/h | 30–60 L | PFU / PFU-S |
| 7.5 kW | 600 m³/h | 60 L | PFH / PFG-S |
A larger cyclone with a larger vortex finder diameter typically causes a pressure drop of about 10 to 15% at normal operating velocity. Compared with the enormous saving in filter life, this is negligible: the side channel blower still delivers around 85 to 90% of its rated power. Please also note: for a vacuum table extraction system with a side channel blower, cyclone volume and hose cross-section should be sized more generously than for a plain industrial vacuum cleaner, because the side channel blower delivers higher volume flows at lower pressures.
BZT Cyclone Separators Compared
BZT offers three sizes of plastic cyclone separators. They differ in collection volume and shift length, not in separation efficiency. The following table compares the three models and their typical areas of use.
| Criterion | Small (20 L) | Standard (30 L) | Large (60 L) |
|---|---|---|---|
| Collection volume | 20 L | 30 L | 60 L |
| Height / diameter | 60 cm / 30 cm | 60 cm / 30 cm | 90 cm / 40 cm |
| Separation efficiency | > 95% | > 95% | > 95% |
| Suitable side channel blowers | 1.1–2.2 kW | 2.2–4 kW | 5.5 kW and more |
| Emptying interval (MDF) | daily | 3–5 days | weekly |
| Price (net, from) | €63.78 | €73.03 | €110.50 |
| Ideal for | Hobby / short shift | CNC workshop | Large format / continuous operation |
In addition, BZT offers compact top-mounted and hybrid separators as well as complete sets with integrated motor and container. For typical CNC vacuum table extraction, however, the three cyclone sizes listed above are the relevant units. You will find hoses, control valves and filters in CNC Accessories, and the matching side channel blowers in the Side Channel Blowers category.
Connecting to CNC Dust Extraction: The Correct Order
The cyclone separator is always installed between the CNC milling machine and the side channel blower, never behind it. The correct order from the machine to the side channel blower looks like this:
- CNC milling machine with dust shoe, connected via a 2-inch hose (NW 50)
- Cyclone separator with tangential side inlet and collection drum at the bottom
- Hose to the side channel blower (NW 50, as short as possible)
- Side channel blower (typically 4 to 5.5 kW)
- Vacuum regulating valve in the suction line (absolutely required)
- Fine dust filter cartridge (5 µm): optional, but recommended for MDF
- Silencer on the pressure side
The most common mistakes when connecting are a hose that is too thin between the cyclone and the side channel blower, which costs 20 to 30% of the volume flow, and a cyclone directly on the vacuum cleaner without a regulating tank, which leads to pulsation and increased filter load. If there is no pre-separator at all, the vortex finders of the cyclone clog quickly. Also make sure to empty the collection drum regularly (weekly in MDF operation) and fit a pre-filter before the cyclone inlet if the machine throws off a lot of chips.
Filter Life: How the Cyclone Protects the Filter
The biggest economic lever of a cyclone separator is protecting the fine dust filter. Without a pre-separator, a fine dust filter cartridge has to be replaced after only 20 to 30 operating hours under heavy MDF load. With an upstream cyclone, the service life increases to 100 to 200 hours. That corresponds to a factor of 5 to 10.
The reason: the cyclone removes around 95% of the volume load before it reaches the side channel blower. The filter only receives the finest dust below 5 µm, which clogs much more slowly. This noticeably reduces the cost of filter cartridges and reduces maintenance of the side channel blower. The material also has an effect here: with pure aluminium, the cyclone alone can often be sufficient and the filter life can rise to 300 hours and more, while wood and MDF fine dust block the filter faster and make a 5 µm filter necessary.
When the cyclone alone is not enough
For pure wood chips, the cyclone is sufficient in many cases. As soon as a significant amount of MDF fine dust arises, however, you should additionally install a 5 µm cartridge filter to protect the airways and to meet the requirements of dust class H. Wood dust is regarded in occupational medicine as hazardous to health, which is why fine dust filtration is not an optional extra but mandatory for panel materials.
Some values cannot be stated across the board because they depend on the material and configuration. Exact pressure drop values of a specific cyclone model, the combined performance of a multi-zone vacuum table extraction system, specific filter replacement intervals per series or the design for special materials such as carbon fibre composites are something we clarify individually. Talk to us about this through our consultation service. We assemble suitable extraction sets of cyclone, side channel blower, tank and filter on request.
Which BZT Series Are Affected?
Extraction with a cyclone pre-separator is particularly relevant for machines with a vacuum table and a side channel blower:
- PFE (professional entry level): Travel ranges X 720–1205 mm and Y 525–1550 mm (clamping surface up to 1250 x 1915 mm), typically with a 4 kW side channel blower and a 30-litre cyclone. Details in the BZT PFE Series category.
- PFU / PFU-S (universal machines): 5.5 kW side channel blower with a 30 to 60-litre cyclone depending on table size. See BZT PFU Series.
- PFH / PFG-S (industrial): from 7.5 kW with at least a 60-litre cyclone and often multi-zone vacuum tables.
To determine the side channel blower and cyclone combination that suits your machine, the Series Comparison Table helps.
Frequently Asked Questions
What percentage of chips does a cyclone separator really remove?
A correctly sized cyclone separator such as the BZT models separates over 95% of wood and aluminium chips before they reach the filter. With coarse, heavy aluminium chips, even over 97% is possible. This saves filter changes and keeps the suction power stable over a long time.
Which cyclone size suits my CNC dust extraction?
As a rule of thumb: for a 4 kW side channel blower, the standard on the PFE and PFJ, the 30-litre size is sufficient. For 5.5 kW and more or for continuous operation, choose the 60-litre version. Hobby users with a 2.2 kW vacuum cleaner also get by with 20 litres.
Must the cyclone separator be installed before or after the side channel blower?
Always before, that is, between the CNC milling machine and the side channel blower. The cyclone separates coarse particles before they reach the side channel blower impeller. An impeller blocked by chips is beyond repair, which is why the correct order is decisive.
Does the cyclone lose a lot of suction?
A 30 or 60-litre cyclone costs about 10 to 15% of the volume flow. Compared with the enormous saving in filter life, this is negligible. The side channel blower still delivers around 85 to 90% of its rated power.
Can I do without the fine dust filter if I use a cyclone separator?
With pure wood chips, yes: the cyclone is sufficient in many cases. With MDF fine dust, however, you should additionally install a 5 µm cartridge filter to protect your airways and to meet dust class H.
How often does the cyclone container need to be emptied?
That depends on the material and shift length: daily when machining MDF, about every 5 to 7 days for aluminium. If the container is more than 80% full, the separation performance drops significantly. With a 60-litre container you save yourself daily emptying, ideal for workshops in continuous operation.
Conclusion and Advice
A cyclone separator is the most cost-effective and most effective measure for reducing the filter costs of your CNC dust extraction and protecting the side channel blower. What matters is matching the size to the volume flow of the side channel blower and the correct connection order. If you are unsure which combination of machine, side channel blower and cyclone suits your material and your shift times, we are happy to advise you. How to size the dust extraction as a whole (airflow, hose cross-section and dust shoe) is shown in the guide Dust Extraction Sizing. Start with the Cyclone Separators category or contact us directly via the consultation page.
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