Views: 0 Author: Site Editor Publish Time: 2026-10-23 Origin: Site
A vacuum table can hold a full sheet perfectly—and still lose the small parts cut from it.
That is because the holding condition changes as the job progresses.
At the beginning, the CNC may be holding one large sheet with plenty of surface area. After dozens of profiles are cut, that same sheet has become many small independent parts.
Less surface area means less vacuum holding force.
Once a part moves, the result can be:
Damaged edges
Incorrect dimensions
Chatter marks
Broken cutters
Scratched material
Scrapped parts
The solution is not always “more vacuum.”
Depending on the material and part size, the better answer may be tabs, onion-skin cutting, smarter toolpath sequencing, mechanical fixtures or a combination of methods.
Here are six practical ways to keep small CNC parts under control.
Situation | Method to Consider |
|---|---|
Small parts cut from full sheets | Onion skin or tabs |
Many nested parts | Toolpath sequencing + vacuum |
Repeated identical small parts | Dedicated fixture or jig |
Irregular / thick parts | Mechanical clamping |
Vacuum weak only after parts are released | Improve zones, sealing and spoilboard |
Thin flat parts with very little holding area | Temporary auxiliary holding may help |
High-risk part movement | Combine two methods rather than relying on one |
The best method depends on:
part size + material + cutting force + production volume + table setup
Vacuum holding depends partly on the surface area available for the vacuum force to act on.
Imagine a full MDF or acrylic sheet.
Before cutting, the vacuum system is holding a large continuous area.
Now cut that sheet into fifty small components.
Each finished component has much less area available for holding.
The vacuum pump has not necessarily become weaker.
The geometry of the job has changed.
This is especially noticeable with:
Small acrylic letters
Narrow plywood components
PVC signs
Small cabinet parts
Detailed nested shapes
Another problem appears once the cutter breaks through the material.
Air can enter through the cut paths, reducing the efficiency of the vacuum system around the remaining workpiece.
That is why small-part holding needs to be considered before the toolpath starts, not after the first part moves.
One of the most common strategies for sheet materials is onion-skin machining.
Instead of cutting completely through the material on the first operation, the CNC intentionally leaves a thin layer at the bottom.
That remaining layer keeps the individual parts connected to the original sheet.
The process may look like:
Main cutting pass
↓
Leave thin bottom layer
↓
All parts stay connected
↓
Final shallow pass removes remaining material
This can work well for:
MDF
Plywood
Some plastics
Nested sheet parts
The vacuum continues to hold the larger sheet rather than trying to hold each individual small part.
Onion-skin cutting depends on consistent material thickness and a reasonably flat table.
If:
Material thickness varies
The spoilboard is uneven
The sheet is warped
the remaining skin may be too thick in one area and disappear completely in another.
So the method needs to be tested with the actual material.
Tabs are small sections intentionally left uncut between the finished part and the surrounding material.
Think of them as temporary bridges.
Instead of allowing the part to become completely free, the tabs hold it in position until machining is finished.
Tabs are especially useful when:
Vacuum area is very small
The part geometry is narrow
The sheet cannot reliably hold the finished component
Part movement would damage the edge
After machining, the tabs are removed manually and the remaining area is finished.
Tabs improve security, but they add post-processing.
The operator may need to:
Cut the tabs
Trim them
Sand or finish the remaining marks
So they are not always the fastest solution for high-volume production.
But when the alternative is losing a part during cutting, tabs can be very practical.
Sometimes the workholding method is acceptable, but the toolpath releases the part too early.
Consider a component that needs:
Holes
Engraving
Grooves
Outside profile
If the outside profile is cut first, the part becomes independent before the other operations are finished.
That makes every later operation more difficult.
A better sequence is often:
Internal features first
↓
Grooves / engraving
↓
Outside profile last
This keeps the part connected to the larger sheet for as long as possible.
For nested production, it may also be useful to think about the order in which groups of parts are released.
The goal is simple:
Do not remove the support before the part has finished being machined.
Good toolpath sequencing can sometimes solve a holding problem without changing the machine at all.
If small parts are normally processed with vacuum, first make sure the vacuum system is operating efficiently.
Check:
Only use the areas needed for the current sheet when the table design allows it.
Open unused areas can waste vacuum capacity.
A damaged, clogged or uneven spoilboard can reduce holding performance.
Check whether unnecessary air is entering around:
Sheet edges
Unused table areas
Fixtures
Cut-through paths
A warped sheet may never seal properly against the table.
If the workpiece covers only a small portion of a large vacuum area, the setup may need to be adapted.
For repeated jobs, a dedicated gasketed area or fixture can sometimes concentrate the holding force more effectively around the actual part.
The important point is:
A bigger vacuum pump is not automatically the first solution.
First check where the vacuum is being lost.
Vacuum is convenient for full sheets.
Mechanical holding can be much more reliable for certain small parts.
Options may include:
T-slot clamps
Custom jigs
Stop blocks
Fixture plates
Dedicated nests
Material-specific holders
This is especially useful for:
Thick parts
Small solid-wood blanks
Irregular components
Light aluminum parts
Repeated identical products
Imagine producing the same small component hundreds of times.
Instead of trying to vacuum-hold every blank individually, a dedicated fixture can position and secure the part in the same location each cycle.
That can improve both:
Holding
Loading consistency
Any mechanical clamp or fixture must remain outside the cutter path.
The CAM program and fixture design should be checked together before production.
Some thin, flat parts have too little surface area for vacuum holding but do not suit traditional clamps.
In selected applications, workshops may use temporary auxiliary holding methods such as:
Machining-grade double-sided tape
Temporary adhesive systems
Sacrificial fixture layers
These methods can help keep small flat parts stable during light machining.
But they should not be treated as a universal solution.
Before using an adhesive method, consider:
Material compatibility
Adhesive residue
Surface finish
Cutting load
Removal method
Whether the part may release during machining
For heavier cuts or higher-risk parts, a properly designed mechanical fixture is generally a more controlled direction.
One of the most useful lessons in small-part machining is that you do not always need to choose only one strategy.
For example:
Vacuum holds the full sheet.
The onion skin prevents small parts from becoming independent too early.
Vacuum supports the main sheet while tabs secure the smallest components.
A fixture controls the part while stops make repeated positioning faster.
The more valuable the part—or the greater the risk of cutter damage—the more reasonable it becomes to add a second layer of security.
Small-part holding is not identical for every material.
Material | Main Holding Concern |
|---|---|
Acrylic | Small letters may lose vacuum quickly after profile cutting |
PVC foam board | Lightweight parts may move once released |
MDF | Full sheets hold well, but very small nested parts can still become unstable |
Plywood | Part movement can worsen edge tear-out |
Solid wood | Irregular shapes often suit mechanical fixtures |
Aluminum | Reliable mechanical holding is especially important because cutting loads can be higher |
The material should influence both the cutting strategy and the holding method.
When a small part starts moving, one reaction is to reduce feed rate.
That may reduce cutting load in some situations, but it does not solve the underlying holding problem.
And on materials such as acrylic, changing feed without considering spindle speed can create another issue—excessive heat.
A better approach is:
Secure the part properly.
Confirm the correct cutter.
Then optimize the cutting parameters.
Workholding should be a foundation of the process, not something compensated for with conservative cutting settings.
If parts are moving, check the problem in this order.
Before full cut-through?
During the final profile?
After it becomes completely separated?
That already gives you an important clue.
A small letter and a full sheet should not be expected to behave the same way on a vacuum table.
Consider:
Onion skin
Tabs
Outside profile last
Check:
Zones
Spoilboard
Leaks
Sheet flatness
For repeated small products, a dedicated jig may be more practical than constantly trying to improve vacuum holding.
If small-part holding is important to your production, send more than the sheet size.
Information | What to Share |
|---|---|
Material | Acrylic, MDF, plywood, aluminum, etc. |
Material thickness | Regular thickness |
Full sheet size | Length × width |
Smallest finished part | Approximate length × width |
Part shape | Square / letter / narrow / irregular |
Current holding | Vacuum / T-slot / clamps |
Production type | One-off / nested sheet / repeated part |
Main problem | Movement / edge damage / lost vacuum |
Required finish | Visible edge / hidden edge / precision fit |
A photo of the nested toolpath or finished parts can be particularly useful.
A supplier who only knows:
“I cut 1220 × 2440 mm acrylic”
may recommend a suitable table size.
But that does not tell them you are cutting 50 mm letters from that sheet.
Vacuum holding force becomes more limited as the available surface area decreases. Once a small part is fully separated from the sheet, it may no longer have enough holding area to remain stable.
It means leaving a thin layer of material at the bottom during the main cutting operation, then removing it with a final shallow pass.
They solve different problems. Vacuum holds the material against the table, while tabs keep individual parts connected to the surrounding sheet. They are often used together.
Mechanical clamps or dedicated fixtures can be very effective for small, thick, irregular or repeated parts, provided the fixture remains clear of the cutter path.
Small-part machining is not only a vacuum-table problem.
It is a combination of:
Holding area
Toolpath sequence
Cutting force
Part geometry
Material
Production method
If a full sheet holds well but the finished parts move, do not immediately assume the vacuum system is too weak.
First ask:
Can I keep the part connected longer?
That may mean:
Onion skin
Tabs
A different cutting sequence
Better vacuum zoning
A fixture
Two methods used together
The safest small part is usually the one that does not become free until the machining is almost finished.
If you are having trouble holding small CNC parts, send UTECH your material, thickness, smallest part size, table type and a photo of the nesting layout. We can help review the workholding strategy around the actual job.
