A vacuum table is one of the biggest conveniences of a panel-processing CNC router: place the sheet, turn on the vacuum and start. But parts moving, especially small parts and during the final passes of a cut, is one of the most common problems operators face.
How does vacuum hold?
The vacuum pump draws air from beneath the table, and atmospheric pressure above the sheet presses it down. So the holding force is directly proportional to the area of the part in contact with the table. As parts get smaller, holding force drops while cutting force stays the same.
The spoilboard
In most panel work the sheet sits on a porous spoilboard placed on the table rather than directly on the table. When the tool cuts fully through the sheet, it goes a few tenths of a millimetre into this layer, so the actual table isn't damaged.
- Over time this surface fills with grooves and marks and starts leaking vacuum.
- Resurface it at regular intervals; this also refreshes its porosity.
- Replace it when it is completely worn.
Why do parts move?
- Leaks: Uncovered areas on the table waste vacuum. Cover unused zones or use a zoned vacuum system.
- Worn spoilboard: An overly porous or deeply grooved surface leaks vacuum.
- Small part area: When the cut is complete the part is fully free around its edges and suction weakens.
- Tool selection: Upcut bits tend to pull the part upward.
- Pump capacity and filter: A dirty filter or undersized pump reduces holding power.
Practical ways to prevent movement
- Leave an onion skin: Don't cut fully through in the first passes; leave a very thin layer at the bottom and remove it in the final pass.
- Use tabs: Leave small parts attached to the main sheet with a few small tabs, then separate them by hand.
- Adjust the cut order: In your CAM software, cut small and inner parts first and large outer contours last.
- The right tool: Downcut or compression bits help press the part onto the table in panel cutting.
- Balance the feed: Lowering the feed rate on the final passes reduces cutting force.
Tip: Watch the vacuum gauge regularly. If the reading drops compared to before on the same sheet type, the problem is most likely the filter, a leak or a worn spoilboard.
Contact us for technical support with your vacuum system, pump or table.