Vacuum chucks
Pressure-difference workholding, effective sealed area, leakage and lateral restraint, with product examples and a bounded force calculation.
Tags: tooling, workholding, vacuum, machining
On this page
A vacuum chuck holds work against a support through pressure difference. Schmalz gives Fn = A × Δp normal force and Fh = A × Δp × μ horizontal resistance: A is evacuated area, Δp pressure difference and μ contact friction coefficient. Schmalz, Vacuum Clamping Technology
Worked example: area and friction
Original illustrative calculation: assume a fully sealed effective area 100 × 80 mm, pressure difference 60 kPa = 0.060 N/mm², and constant μ = 0.25:
A = 100 × 80 = 8,000 mm²
Fn = 8,000 × 0.060 = 480 N
Ideal lateral resistance = 0.25 × 480 = 120 N
Halving area at unchanged pressure difference gives 240 N normal and 60 N lateral. These static estimates exclude peaks, leakage and overturning. A through-cut can open the seal, reducing effective area and pressure difference.
Effective area and leakage
The pressure difference is bounded by the surrounding absolute pressure: a pump cannot create negative absolute pressure. A gauge reading referenced to atmosphere and an absolute-pressure reading therefore mean different things. As physical interpretation, “−0.8 bar gauge” describes an 0.8 bar difference under the stated ambient reference, not a negative absolute pressure.
The relevant area is the region actually evacuated and sealed beneath the part, not necessarily the chuck's outside footprint or the part's projected outline. Separate chambers, gasket paths, open holes and exposed passages change that region.
Schmalz's CMB-HD instructions 30.30.01.03560, revision 01, 08/23 warn that drilling through a suction area or damaging its sealing lip can cause sudden vacuum loss. It also covers permeability, generator flow, coolant-reduced friction, leverage and stops for horizontal loads. Schmalz, CMB-HD instructions, pp. 13–15
Engineering synthesis: vacuum level and air-flow capacity are different specifications. A generator's low-pressure capability under sealed conditions does not establish the pressure it maintains while air enters through porous stock or a newly opened cut. Pressure at the actual chuck can also differ from a reading elsewhere in the supply system.
A part becoming separate from the surrounding blank can lose both effective area and mechanical support. A gasketed metal-cutting setup and a high-flow arrangement using a sacrificial layer are therefore different systems, even when both are called vacuum tables.
Normal force, shear and overturning
| Load or property | Meaning | Separate limitation |
|---|---|---|
| Normal holding force | Net pressure force toward the support | Depends on effective area and pressure difference |
| Lateral restraint | Resistance to sliding | Friction and any mechanical stops participate |
| Overturning/peeling | Moment tending to unload or lift an edge | Force application point and contact distribution matter |
| Support stiffness | Resistance to workpiece deformation | A large total force does not guarantee local support |
This table is a mechanical interpretation. Cutting loads vary through engagement and include peaks; their direction matters. A tall workpiece can overturn under a lateral force even when a simple sliding calculation looks favorable. Thin sheet can be held down overall while deflecting locally over a cavity.
A bounded Schmalz example illustrates the force distinction: its CMB-HD-D120-69-RB, 10.01.27.01874, has theoretical 905 N vertical and 362 N horizontal force at −0.8 bar, on dry aluminum with assumed μ = 0.4. These are the manual's calculation conditions, not universal cutting-force allowances. Schmalz, CMB-HD theoretical forces, p. 14
Different product arrangements
Datron Technology's February 21, 2022 explanation describes its VacuCard sacrificial layer: through cuts enter the card rather than the table. That explains protection of the underlying table; it does not establish that every through-cut geometry retains enough vacuum holding force. Datron Technology, vacuum-table explanation
Mitee-Bite's Roto-Vac Gen II is a rotary arrangement for a lathe or rotary table. Its face has nine gasket grooves and 32 M6 gripper holes. The page identifies a 1,100 rpm rotary-fitting design limit, recommends light-duty applications and notes that its grippers indent the workpiece backside. A fitting-speed figure is not an assembled workpiece balance or cutting-capacity guarantee. Mitee-Bite, Roto-Vac Gen II
These examples show why the vacuum source, sealing layout, support surface, mechanical attachment and machining strategy form one workholding system. Flatness and surface appearance requirements remain relevant even when conventional jaws are absent.
Coverage and source dates
The Schmalz manual prints revision 01 and 08/23; Datron's article prints 21/02/2022. No technical issue date was established for the Schmalz glossary or Mitee-Bite page. Sources were inspected on November 2, 2026; copyright and search dates are not revisions.
This reference does not establish universal vacuum level, flow, friction, minimum part area, spindle speed, cutting force or surface-finish guarantee. Workpiece condition, actual contact, generator performance and machine integration remain application-specific. Product examples do not establish a shop's installed equipment or approved restraint conditions.
Related reference
Choosing workholding compares location, support and restraint across fixture types.