The Physics of Holding a Part With Air
A vacuum chuck plate holds a workpiece because the pressure under it is lower than the pressure above it. At full vacuum the clamping force is roughly one kilogram per square centimetre, so a part covering 200 square centimetres sees about 200 kilograms. That is enough for finishing and light roughing, and it is why a vacuum plate is normally paired with a mechanical stop rather than used alone for heavy cuts.
Groove Geometry Decides the Force
- Concentric rings suit round and square parts, with a cross groove so vacuum reaches the whole footprint even when one ring falls outside the workpiece.
- Grid patterns serve mixed part sizes, with plugged ports to isolate unused zones.
- Groove size: 2 mm to 4 mm wide and 1.5 mm to 3 mm deep, sized so the groove volume does not exceed the pump capacity.
- Seal: an O-ring groove for parts needing a hard stop, or a flat land for gasket tape on general purpose plates.
Why Flatness Is the Function
Leakage scales with the gap between part and plate. A plate out of flat by 0.05 mm will hold a thin part poorly no matter how large the pump is, and the operator will blame the pump. Our working face flatness is 0.01 mm up to 300 mm and 0.02 mm above that, with parallelism to the machine table face held at 0.01 mm so the plate does not need shimming.
| Property | Value | Test |
|---|---|---|
| Working face flatness | 0.01 mm up to 300 mm | Granite plate, grid of points |
| Parallelism to table face | 0.01 mm | Height gauge on granite |
| Vacuum integrity | Five minute decay | Capped ports, pressure decay record |
Stress Relief Before Finishing
Hogging out a groove network releases stress in the plate. Plates are rough machined, stress relieved, then finished, and the grooves are cut after the face is finished with a light pass so the groove edges do not raise a burr above the sealing surface. Hard anodizing is applied with the groove edges masked, because coating build up can close a groove and change the leak rate.
What to Specify When Ordering
- Part footprint, part material and the heaviest cut the plate must survive
- Pump capacity, so the groove volume can be matched to it
- Machine table pattern, for the mounting holes and reference edge
- Whether the plate needs multiple zones for several small parts at once
Specifications and options for the vacuum chuck fixture plate are listed with each plate shipping with a flatness report and a decay test record.
