Tabs and onion skinning: holding parts through a cut
Tabs are small uncut bridges holding a part in the sheet. Onion skinning leaves a thin continuous layer across the whole cut instead. Tabs are quick to cut off and leave marks. Onion skin leaves no marks and takes longer to clean up.
The problem they solve
The moment a profile cut finishes its last pass, the part is free. A free part under a spinning cutter gets grabbed, spun, and thrown. It ruins the part, it can break the bit, and it is genuinely dangerous.
Tabs
Small sections of the profile that are not cut to full depth, leaving a bridge of material between the part and the sheet.
| Decision | Guidance |
|---|---|
| How many | At least four on anything of size. More for heavy parts, small parts and parts with long thin sections. |
| Where | On straight edges you will clean up anyway. Never on a curve you want to stay smooth, never in a corner. |
| How thick | Thick enough to hold, thin enough to cut with a flush trim saw or a chisel. Often around a sixteenth of an inch in wood. |
| How wide | Wider is stronger. A short tall tab is harder to cut off than a long low one. |
| Shape | Ramped tabs, where the tool rises and falls rather than stepping, are gentler on the machine and the bit. |
Onion skinning
Instead of cutting through and leaving bridges, stop the cut a small distance above the bottom, often around 0.01 to 0.02 inches, across the whole profile. The part stays attached by a continuous thin membrane.
| Tabs | Onion skin | |
|---|---|---|
| Part security | Good | Excellent, nothing can shift at all |
| Edge quality | Marks at each tab | Clean all the way round |
| Cleanup | Cut a few tabs, sand the marks | Cut or sand the whole perimeter |
| Best for | Larger parts, thicker material | Small parts, thin material, delicate shapes, anything where edge quality matters |
| Risk | A tab breaks and the part moves | The skin is too thick and cleanup is a chore, or too thin and it tears |
When you need neither
If the workpiece is held down over its whole area, by vacuum or by double sided tape across the full face, parts often stay put without tabs. This is genuinely how production shops cut small parts. The caution is that vacuum loses grip on very small parts as their area shrinks, and tape lets go if an upcut bit lifts hard enough. For small parts, use tabs as well, not instead.
Cutting tabs off well
- A flush trim saw cuts a tab off level with the edge with almost no cleanup.
- A sharp chisel works well in wood if you cut with the grain.
- A knife is fine for thin material and plastics.
- Snapping them tears the edge and pulls a chunk out of the part. It is quick and it looks it.