Tabs vs Onion Skin for CNC Profile Cutting

Tabs are local bridges

Tabs preserve material at selected points. Place enough to resist likely translation and rotation, avoid fragile corners where possible and consider grain or veneer weakness. Vectric distinguishes 2D tabs with vertical motion from ramped 3D tabs; software behavior and dimensions must be reviewed in simulation.

Onion skin is a continuous remainder

The profile stops short of full depth, leaving a thin layer around the part. It can preserve vacuum area and reduce individual tab cleanup, but variation in sheet thickness, stock warp or spoilboard plane can cut through unexpectedly or leave a layer too thick for the finishing pass.

Use measured material values

Nominal sheet thickness is not enough. Measure the production stock and reference plane. If a compression bit or finishing tool is involved, confirm how the retention strategy interacts with its geometry and pass depth. Never set a deeper final cut merely to compensate for unknown variation without checking table clearance.

Plan the release operation

A final pass removes the onion skin and can release every part quickly. Tabs release later during manual cleanup. Decide how parts and offcuts remain controlled at that moment. Order internal features before outside profiles and keep hands away until motion and spindle have stopped under the machine procedure.

Inspect the first nested sheet

Watch directly, check whether small parts vibrate and pause if retention weakens. Measure remaining skin or tabs after the first representative part. Update the setup from evidence rather than waiting for an ejected component.

Plan the release operation

Retention is not complete until the part can be separated without damage. Decide where a hand tool can safely reach, how the machine will be isolated and where the released part will be placed. Put tabs on robust, accessible edges and avoid cosmetic surfaces or narrow details that are difficult to trim.

Verify the final layer

Onion skin thickness depends on actual stock thickness, spoilboard condition and Z reference accuracy. Test the remaining layer and observe whether small parts shift during the final pass. A strategy that works on a large rectangle may fail on a narrow component because available vacuum area and cutting force are different.

Decision table

Practical checklist

1. Measure actual stock and table plane.
2. Place retention away from weak features.
3. Simulate release order.
4. Inspect the first part before continuing.

Frequently asked questions