CNC Workholding Guide
Workholding is the foundation of accurate machining. The right fixture reduces setup time and improves repeatability.
Vise Selection
| Type | Force | Parallelism | Best For |
|---|---|---|---|
| Hydraulic vise | 10-30 kN | ±0.005mm | High prod, thin-wall |
| Pneumatic vise | 5-15 kN | ±0.01mm | Quick-change, medium vol |
| Manual precision | Variable | ±0.005mm | Job shop, low vol |
| Self-centering | 5-20 kN | ±0.02mm | Round/symmetrical parts |
Soft Jaws
Machined to match part contour for maximum contact and minimal distortion. Cut jaw pocket 0.1-0.3mm smaller than part for press fit. For thin-wall parts (<2mm), use 70-80% clamping force and add support bar to prevent collapse.
Modular Fixturing
- Zero-point clamping: Quick-change pallets, ±0.002mm repeatability, 10-30s swap time
- Sub-plates: Pre-drilled grid pattern (M12/M16 on 50-100mm centers), most flexible for job-shop
- Dovetail fixtures: Hold parts by pre-machined dovetails, provides 5-axis access
Vacuum Workholding
For thin flat parts where clamps cause distortion. Min part thickness: Al 0.5mm, plastic 1mm. Holding force ~6-8 N/cm² at 0.6-0.8 bar. Fixture flatness ≤0.025mm/300mm.
Setup Time Reduction
- Use probing cycles for datum establishment (80% time reduction)
- Pre-set fixtures off-machine
- Torque-limiting drivers for consistent clamping
- Store complete fixture assemblies, not components