CNC ROUTER NESTING & VACUUM WORKHOLDING

CNC Vacuum Hold-Down Tab Retention & Onion Skin Calculator

Compute vacuum holding force vs tool cutting thrust, determine required bridge tab dimensions and spacing, calculate 3D ramp slopes, and calibrate 2-stage onion-skinning floor thickness to prevent small parts from moving or lifting during high-speed CNC routing.

1. Part Geometry & Workholding

Substrate Material & Shear Strength

Part Top Face Surface Area [cm²]

Small parts (< 200 cm²) have high risk of vacuum loss.

Part Perimeter Cut Length [mm]

Sheet Thickness ($T$) [mm]

2. Tooling & Cutting Forces

Router Endmill Diameter ($D$) [mm]

Vacuum Bed Pressure (Negative Pressure) [kPa]

Standard rotary claw pump generates 60-80 kPa vacuum under spoilboard.

Workholding Force vs. Tool Thrust

Vacuum Holding Force

119.3 kgf

1,170 N clamping force

Cutting Lateral Thrust

18.5 kgf

Peak side tool load

Holding Safety Factor

6.4x

Secure holding

Recommended Tab Count

3 Tabs

Spaced every ~180 mm

Bridge Tab & Onion-Skin Specifications

Bridge Tab Width ($W_{\text{tab}}$)

6.0 mm

Along cutting perimeter

Bridge Tab Height ($H_{\text{tab}}$)

1.8 mm

10% of sheet thickness

3D Ramp Entry Angle

30.0°

Eliminates dwell marks

Onion Skin Floor Thickness

0.65 mm

For 2-stage skinning pass

CAM Toolpath Layer Strategy

                        PASS 1 (ROUGHING): Cut to depth 17.35 mm (leave 0.65 mm skin)

                        PASS 2 (CLEANUP): Full depth @ 150% feed rate to sever onion membrane

                        3D_TABS: Triangular ramps (3 places @ $30^\circ$ slope)