Why Hold-Down Tabs Matter on a CNC Router
Cutting a part fully free of its surrounding stock mid-program is risky, the part can shift, lift into the spindle, or get thrown by the cutter the instant the last connection lets go. Leaving small uncut tabs around the perimeter keeps the part anchored to the spoil board or surrounding sheet until you're ready to break it free by hand or with a final pass.
Spacing Tabs Evenly Around the Perimeter
Dividing the part's perimeter by your target spacing and rounding up gives a whole number of tabs that fit evenly around the cut, which keeps the holding force balanced rather than concentrated on one side. Heavier, denser materials and parts with a lot of unsupported overhang generally want closer tab spacing than light, well-supported parts.
Placement Is Only Half the Job
Knowing how many tabs to place and how far apart only solves the layout problem, you still need to decide how thick to leave each tab so it holds the part but still snaps free cleanly, which is a separate decision driven mostly by material thickness and brittleness rather than perimeter length.