Slide 001: Workholding Methods for CNC Routing¶

Slide Visual¶

Workholding Methods for CNC Routing

Slide Overview¶

This slide presents the major workholding methods used in CNC routing, comparing their strengths, limitations, and appropriate applications. Proper workholding is the single most important safety factor in CNC operation.

Instruction Notes¶

Why Workholding Matters¶

Cutting forces in CNC routing can reach 10-50 lbs depending on material, tool, and parameters. If the workholding force is less than the cutting force, the material WILL move. A loose workpiece is the most dangerous failure mode in CNC routing — it can be thrown from the machine at high speed.

Mechanical Clamps¶

Types: Toe clamps, cam clamps, step clamps, bar clamps - Holding force: High (50-500 lbs per clamp depending on type) - Best for: Thick stock (¾"+), irregular shapes, one-off jobs - Limitations: Obstruct tool travel — must be positioned carefully outside toolpaths; require T-slots or threaded inserts in the bed - Critical rule: Clamps must be BELOW the retract height and OUTSIDE the toolpath boundary plus tool radius

Screw-Down¶

Direct screws through the workpiece into the spoilboard. - Holding force: Very high per screw (100+ lbs pullout in MDF) - Best for: Production runs, plywood, material where screw holes in waste area are acceptable - Limitations: Requires waste area for screw placement; screws are tool breakers if hit - Typical hardware: #8 or #10 wood screws, 1.5"–2" long, with fender washers

Double-Sided Tape¶

Carpet tape or machinist's double-sided tape between material and spoilboard. - Holding force: Moderate (5-15 PSI depending on tape quality and surface area) - Best for: Thin material, full-sheet cuts, situations where clamps would interfere - Limitations: Requires clean, flat surfaces; may not hold for aggressive cuts; residue cleanup - Pro tip: Apply tape in parallel strips covering 50-70% of the surface area; press firmly with a roller

Vacuum Table¶

Vacuum pump creates suction through holes or channels in the spoilboard. - Holding force: ~12 lbs per square inch at full vacuum (25" Hg) - Best for: Large sheet goods, production work, non-porous materials - Limitations: Poor hold on small parts (low surface area); porous materials (wood end-grain) leak vacuum; requires dedicated vacuum pump (5-10 HP) - Gasket: Use foam weatherstrip or rubber gasket around the perimeter to seal between spoilboard zones

Hybrid Methods¶

Combining methods often provides the best results: - Tape + clamps: tape holds center, clamps secure edges - Screws + tabs: screws hold waste, tabs hold parts after cutout - Vacuum + tape: vacuum for primary hold, tape for small parts in low-vacuum zones

Key Talking Points¶

Workholding failure is the #1 cause of CNC routing incidents
Match the workholding method to the material, cut type, and part geometry
Mechanical clamps are the most versatile but require careful positioning
Double-sided tape is underrated — it works extremely well for sheet goods
Always test workholding before starting the spindle — try to move the material by hand

Learning Objectives (Concept Check)¶

[ ] Describe 4 workholding methods and their appropriate applications
[ ] Calculate approximate vacuum hold force for a given part size
[ ] Explain why hybrid workholding methods are often superior

Last Updated: 2026-03-19