Vacuum clamping is the fastest and at the same time gentlest clamping method for sheet material on a CNC gantry milling machine. Instead of fiddling with screw clamps, hold-downs or double-sided tape, you simply place the workpiece on the table, switch on the pump, and can mill almost right up to the edge. That saves setup time, avoids pressure marks and allows full-surface machining such as grooves, pockets or edges in a single pass.
The catch: the vacuum table itself is only half the story. Whether the clamping really holds is decided by the combination of table and vacuum pump, and this is exactly where most mistakes happen in practice. A table with too large an area and a weak pump do not pull the workpiece down firmly. A rotary vane pump in a dusty MDF production is a maintenance case after a few months. And without a pre-filter, every pump breaks down sooner or later. This guide shows which types of vacuum table exist, which pump suits which application and how you can calculate the holding force realistically.
Vacuum Table Types at a Glance
Before we get to the pump, it is worth looking at the table types. Each has its strengths; the choice depends above all on which materials and workpiece sizes you machine.
Grid Table
The classic industrial vacuum table: an aluminium or steel plate with a milled hole grid (typically 30 x 30 mm or 50 x 50 mm) and grooves for sealing cords. You lay the sealing cord around the workpiece contour, cover unneeded holes with film or tape and pull the workpiece down directly. Advantage: very high holding force, ideal for aluminium, composites and precise workpieces. Disadvantage: higher setup effort, because sealing cords have to be laid anew for every workpiece.
MDF Spoilboard
An MDF board with holes that acts as an air-permeable spoilboard. The vacuum pulls through the open porosity of the MDF material; the workpiece only has to lie flat, and no sealing cords are needed. Very popular in furniture making and sign making, because you can simply resurface or replace the spoilboard once it is worn. Disadvantage: significantly lower holding force than with the grid table, because a lot of leakage air is drawn in. Works only with pumps with a high volume flow.
Slotted Table
A hybrid solution: aluminium profiles with longitudinal slots into which T-slot nuts, vacuum channels or clamping elements can be inserted. Often used on CNC gantry milling machines for furniture production, because the table can be used both with vacuum and with mechanical clamping devices. Well suited to changing workpieces and combined clamping setups.
Multi-Zone Table
The premier class: the table is divided into two, four or more zones that are switched on or off individually by solenoid valve or ball valve. This way you clamp small workpieces over one zone only, without the other areas drawing leakage air. In combination with programmable valves, even clamping setups for double panels or batch production can be automated. Worthwhile as soon as you regularly produce different workpiece sizes.
Which pump for which application?
The most important decision is the pump type. Three designs have become established in CNC machining, each with clear advantages and disadvantages. The following table summarises the differences:
| Criterion | Side channel blower | Rotary vane vacuum pump (oil-lubricated) | Dry-running rotary vane pump |
|---|---|---|---|
| Operating principle | Impeller creates suction by accelerating the air | Rotor with vanes, oil film seals | Rotor with graphite or plastic vanes, without oil |
| Vacuum (mbar) | approx. 100–250 mbar (measured as negative pressure) | up to 0.1 mbar ultimate vacuum possible | up to approx. 100 mbar ultimate vacuum |
| Volume flow (m³/h) | very high: 100–1000+ m³/h | medium: 25–300 m³/h | medium: 25–250 m³/h |
| Dust tolerance | high (with pre-filter) | very low: chips destroy the vanes | low: dust significantly increases wear |
| Maintenance | low: check filter, bearings every few years | high: oil changes, filter, regular inspection | medium: vane replacement every 1000–3000 h |
| Noise level | loud (70–80 dB), silencer recommended | moderate (60–70 dB) | moderate (60–70 dB) |
| Purchase cost | medium | medium to high | high |
| Recommended application | Wood, MDF, spoilboards, large tables, dusty environments | Glass, film, metal, clean workpieces, high holding force | Clean room, food, packaging, medium holding force |
In a classic joinery or sign-making shop, the choice usually falls on a side channel blower: it is robust, tolerates dust without problems with a pre-filter and delivers the high volume flow that an MDF spoilboard needs. In metalworking or with film and glass applications, the rotary vane pump scores with a significantly higher ultimate vacuum, but only if the workpieces and the environment are clean.
The Dust Problem: Why the Choice of Pump Is Decisive
This is exactly where most vacuum solutions fail in practice. Anyone milling wood, MDF or plastic produces huge amounts of chips and fine dust. When drilling a hole grid through an MDF spoilboard, fine dust is literally sucked into the vacuum line. An unprotected rotary vane pump does not cope with that for long: the vanes run dry, the oil film breaks down, the lubricating oil emulsifies with wood dust into a greasy paste, and after three to six months the pump is an economic write-off.
A side channel blower is much more tolerant here because the impeller works without contact. There are no vanes that can wear out. Even so, a side channel blower also needs a pre-filter, otherwise the silencer clogs and the volume flow collapses. So if you mainly machine wood, MDF, HPL or composites, the order is clear: first choose the right pump type, then pay attention to good filtration. The table under Series Comparison shows which BZT models are recommended as delivered for wood or mixed applications.
Pre-Filters and Cyclone Separators as Protection
The right filter strategy extends the life of your vacuum pump drastically. Best practice in wood and panel machining is a combination of two stages.
Stage 1, cyclone separator: The coarse portion of chips and fine dust is separated from the airflow by centrifugal force before it even reaches the pump. A good cyclone separator removes 95–99% of the particles and relieves the downstream filter considerably. The collected dust falls into a collection container that is simply emptied, with no costly filter cartridge logistics.
Stage 2, fine filter: A fine filter (typically 5–25 µm) sits directly in front of the pump and retains the remaining portion. A washable polyester or paper filter is usually enough here. Important: check the filter regularly, because a clogged filter causes pressure loss and reduces the usable vacuum at the table.
Anyone who takes this seriously often runs the pump for five to ten years with little maintenance. Anyone who forgets the filter sees it again after just a year, at the service centre. You will find suitable components under CNC accessories.
Multi-Zone Vacuum Tables: When Is It Worth It?
A multi-zone table divides the table surface into independently switchable zones, usually 2, 4 or 6 sectors. Using pneumatic ball valves or electric solenoid valves, you activate only the zone on which your workpiece sits. The rest stays closed, so no leakage air uses up the volume flow.
When is it worth it?
- Small workpieces on a large table: A 1500 x 3000 mm table with a spoilboard draws an enormous amount of leakage air if only a 300 x 400 mm workpiece lies on it. Zone switching reduces the effective suction area and concentrates the vacuum, so the holding force rises significantly.
- Changing workpiece sizes: Anyone who makes furniture fronts one day and small parts the next benefits enormously from flexible switching.
- Double clamping: While one zone is being machined, the other can be loaded, which keeps machine downtime minimal.
In professional machines such as the BZT PFU series or the BZT PFE, a multi-zone division with electric valve control can be programmed via the controller. This even allows clamping setups to be specified in the CAM program.
Calculating Holding Force: Is the Vacuum Enough?
Before you decide on a table and a pump, you should roughly estimate the holding force. The rule of thumb is simple:
In practice, this means: if you work in wood with a 6 mm finishing cutter, 100–150 mbar is plenty. But anyone roughing aluminium with an aggressive depth of cut should plan for at least 200 mbar and a grid table with sealing cord, or help out mechanically as well. A sufficiently sized high-frequency (HF) spindle, by the way, reduces the required holding force, because it works more cleanly and with less depth of cut.
Spoilboard Tips: Surfacing and Sealing MDF Correctly
A good spoilboard is custom work. These points pay off:
- Choice of material: Medium-hard MDF in 19 or 25 mm thickness. Boards that are too soft clog up, boards that are too hard draw poorly.
- First surfacing: After screwing it down, mill it completely smooth in one pass with a facing cutter, which creates the flat suction surface.
- Edge sealing: Seal the outer edges and the underside with wax, lacquer or aluminium adhesive film so that the vacuum does not escape sideways.
- Not too thick: The thicker the MDF, the higher the flow resistance. 19 mm is a good compromise between stability and suction performance.
- Regular resurfacing: If the spoilboard is roughened by milling marks or dirty, resurface half a millimetre instead of replacing it completely.
Over time, every spoilboard loses suction performance through contamination. Rule of thumb: replace it after 6–12 months of full load. A table with a well-maintained spoilboard is often the decisive difference between a machine that produces and one that constantly causes stress; you will find more on this in our article on lubrication and cooling, where we apply the same maintenance thinking to the spindle and guides.
Connection to the CNC Machine: Hoses, Couplings, Pressure Gauge
An often underestimated point: the line between pump and table. Poor hoses or undersized couplings can swallow up to 30% of the suction performance.
- Hose diameter: At least 32 mm inner diameter for side channel blowers, better 50 mm. Rotary vane pumps often manage with 25 mm.
- Hose type: Steel spiral hoses or reinforced PU hoses; standard PVC collapses under negative pressure.
- Short runs: Place the pump as close to the table as possible; every bend costs suction performance.
- Pressure gauge: Mount it directly at the table so that you can see live whether the clamping holds, a mandatory tool in daily production.
- Emergency shut-off: A simple toggle switch or a solenoid valve with which you can quickly switch off the vacuum (e.g. if a workpiece breaks).
Anyone who installs it cleanly once has peace for years. If you are unsure which components suit which BZT PFA machine or a larger PFU, it is worth calling our technicians via Contact; they know the connection geometries of the various table variants in detail.
Frequently Asked Questions
Which vacuum pump is the best for a CNC milling machine with a vacuum table?
The most universal choice is a side channel blower with 200–400 m³/h volume flow. It is dust-tolerant, low-maintenance and provides enough leakage air reserve for MDF spoilboards. For glass, film or pure aluminium applications, an oil-lubricated rotary vane pump is the better choice because of the higher ultimate vacuum. With a lot of dust or changing operation, the following applies: side channel blower plus cyclone separator and fine filter.
Is a side channel blower enough if I have a lot of dust?
Yes, it is even the recommended solution for dust-intensive applications such as wood, MDF or plastic. However, only in combination with a cyclone separator and a fine filter, otherwise the silencer clogs and the suction performance collapses. Rotary vane pumps, on the other hand, are unsuitable in a dusty environment and become uneconomical through wear after a few months.
How high should the vacuum be at a minimum?
For wood and plastic, 100–150 mbar of negative pressure at the table is sufficient, provided the suction area is large enough. For aluminium or small workpieces, you should plan for 200 mbar or more. What matters is not only the ultimate vacuum of the pump but the negative pressure that actually arrives at the table; a lot is lost through leakage air, filter resistance and poor hoses.
Can I also hold thin workpieces without clamps?
Yes, that is precisely the strength of a vacuum table. Thin veneers, films or sheets that could not be held with screw clamps without pressure marks can be machined perfectly under vacuum clamping. For very thin workpieces such as films, a tight MDF spoilboard and a pump with a high ultimate vacuum (rotary vane) make sense, because the workpieces otherwise let air through.
How large does the pump need to be for my table surface?
Rule of thumb for MDF spoilboards: allow approx. 100–150 m³/h of volume flow per square metre of table surface. For a 1500 x 3000 mm table (4.5 m²), that would be roughly 450–700 m³/h. With a multi-zone division, you get by with smaller pumps because only one zone is active at a time. With grid tables with sealing cord, considerably less is usually enough because the suction area is tightly limited.
Conclusion: Think of Table and Pump as a System
A vacuum table is only as good as the pump that supplies it, and both only as good as the filter strategy behind them. Anyone milling wood and MDF is most relaxed with a side channel blower and an MDF spoilboard, provided a cyclone separator and fine filter are consistently installed. Anyone machining aluminium or films needs a higher ultimate vacuum and is better served with a grid table plus rotary vane pump.
If you are unsure which combination suits your machine and your material mix, take a look at our series comparison table, where you will find the recommended clamping configurations by model size. For an individual design of your vacuum system, including pump selection, filter concept and connection, speak to our technicians via Contact. We will help you match the components so that your next clamping really holds.
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