Without secure clamping there is no precise machining. But which workholding is the right one? Vacuum table, T-slots, screws or even adhesive tape? This comparison helps you choose.
Why Clamping Matters So Much
Clamping has to do two things:
- Hold firmly: the workpiece must not move, even under cutting force
- Not deform: the clamping force must not bend or dent the part
These requirements are often in conflict, especially with thin or delicate parts.
How you meet both requirements depending on the workpiece, and what additional demands automotive and aerospace place on repeatability and low-distortion clamping, is explained in the guide CNC fixtures: clamping workpieces correctly.
Workholding Compared
T-Slots with Strap Clamps
The classic: metal clamps press the workpiece onto the table.
Advantages:
- Very high clamping force possible
- Flexible for different shapes
- Inexpensive to buy
- No wear on the clamping system
Disadvantages:
- Time-consuming set-up
- Clamps in the working area (risk of collision)
- Restricted accessibility
- Risk of distortion with thin parts
Ideal for: 3D parts, solid workpieces, one-offs, prototypes
Vacuum Clamping
Negative pressure holds the workpiece down on a vacuum plate.
Advantages:
- Very fast clamping and releasing
- The entire surface is freely accessible
- Even pressure without deformation
- Ideal for series production
Disadvantages:
- Higher investment costs
- Not for porous materials (wood only to a limited extent)
- Minimum size required
- Cutting through requires a spoilboard
Ideal for: sheet machining, plastic, coated boards, series production
Screwing Down onto a Spoilboard
The workpiece is screwed directly onto an MDF spoilboard.
Advantages:
- Absolutely secure: the part cannot slip
- Very simple and inexpensive
- Suitable for any material
- Also for uneven parts
Disadvantages:
- Holes in the workpiece
- Screw heads in the working area
- Time-consuming for series
- The spoilboard has to be replaced
Ideal for: prototypes, parts with hidden areas, uneven materials
Double-Sided Adhesive Tape
Industrial mounting tape holds the workpiece in place.
Advantages:
- Quick and easy
- No clamp marks
- The entire surface is accessible
- Inexpensive
Disadvantages:
- Limited holding force
- Only for light cuts
- Adhesive residue on the workpiece
- Not reusable
Ideal for: thin sheets, engraving, light fine work
Machine Vice
A machine vice clamps the part from the side.
Advantages:
- Very high clamping force
- Fast clamping
- Repeatable
Disadvantages:
- Only for rectangular parts
- The part stands high (Z range reduced)
- Access from above only
Ideal for: small aluminium parts, series production of identical parts
The Big Comparison
| Criterion | T-slots | Vacuum | Screws | Adhesive tape | Vice |
|---|---|---|---|---|---|
| Set-up time | Slow | Fast | Medium | Fast | Fast |
| Holding force | Very high | Medium to high | Very high | Low | Very high |
| Accessibility | Restricted | Excellent | Restricted | Excellent | From above |
| Risk of distortion | Medium | Low | Low | None | Medium |
| Investment | Low | High | Minimal | Minimal | Medium |
| Series production | Limited | Excellent | Poor | Limited | Good |
Combinations and Special Solutions
Vacuum + T-Slots
Many users combine the two: vacuum for sheet material, T-slots for 3D parts. Our gantry mills can be equipped with both systems.
Spring-Loaded Hold-Down Clamps
Spring-mounted hold-down clamps press the part down from above while the cutter is working. Good for thin sheets.
Slotted Plate with Threaded Inserts
Instead of T-slots: a plate with a grid of threaded holes (e.g. M8). More flexible than T-slots, and quicker to change over.
Modular Clamping Systems
Professional clamping systems with quick-change elements. Expensive, but very efficient for series production.
Decision Guide: Which System Is Right for You?
Mainly Sheet Machining (Wood, Plastic)
Recommendation: vacuum table
The investment pays off through fast changeover times and full accessibility.
Mixed Use (Sheets and 3D Parts)
Recommendation: T-slots + optional vacuum attachment
Maximum flexibility. T-slots as the basis, with vacuum placed on top when needed.
Mainly Small Aluminium Parts
Recommendation: vice + T-slots
High clamping force for metalworking, fast clamping for series.
Prototypes and One-Offs
Recommendation: T-slots + screws
Flexibility is more important than speed.
Practical Tips
Take Cutting Forces into Account
The cutting force mostly acts sideways. Clamp so that this force is absorbed, and do not rely only on pressing down from above.
Use a Spoilboard
When cutting all the way through, always place a spoilboard (MDF, hardboard) underneath. It protects the table and allows a complete cut-through.
Plan the Clamping Setup
Think before programming: how will the part be clamped? Where are the collision points? This saves trouble later.
Allow a Reserve
It is better to over-dimension slightly. If the clamping force only just suffices, things become critical with heavier machining.
FAQ: Frequently Asked Questions
Can I clamp wood with vacuum?
To a limited extent. Solid wood is porous and lets air through. Coated chipboard, MDF with a sealed surface and plastic work well. With solid wood, use sealing tape at the edge or choose an alternative.
How much vacuum do I need?
Typical: 0.8 bar negative pressure (80% vacuum). On an area of 1000 cm² this gives roughly 800 kg of holding force, more than enough for most applications.
What T-slot width is standard?
14 mm is the most common. Matching clamping elements are available everywhere. Some machines also have 10 mm or 18 mm slots.
Conclusion: The Right System for Your Application
There is no universally best clamping system, only the best one for your application. Most users benefit from a combination:
- Basis: T-slot table for maximum flexibility
- Extension: vacuum module for sheet machining
- Addition: vice for small parts
Related Accessory Guides
Do you want to equip your machine properly? We will be glad to advise you on the right clamping system for your application.
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