A lead-in scar carries information about where the cutter entered, how it loaded, and which finished surface received the transition. Preserve the mark, compare it with the programmed path, and change entry location or motion only after ruling out play, deflection, and stock movement.
Preserve the Entry Scar Before Sanding
Before touching lead settings, mark the programmed entry and exit points on a toolpath image and transfer their location to the cut. A witness exactly at those transitions supports a lead investigation. A mark that repeats at every corner, at each depth level, or only on one machine axis belongs to a different diagnostic branch.
Separate Geometry From Machine Motion
Describe the mark physically. A raised burr, inward gouge, outward bump, matte patch, and burnished line do not represent the same force history. View the wall with raking light before deburring and measure the feature where possible. A general note such as ‘lead scar’ discards the evidence needed to choose the next test.
Move the Lead Away From the Cosmetic Zone
Check whether the lead has room to settle before it reaches the finished boundary. Short arcs can ask the machine to change direction while the cutter is still recovering from entry load. On small profiles, a tangential extension or a different start area may help, but only if it stays within stock and fixture clearance.
Control the Engagement Change
Separate geometry from load by cutting a light finishing coupon and a representative engagement coupon with the same lead location. If the scar appears in both, examine path continuity, backlash, runout, or a dwell-like transition. If it emerges only under load, investigate deflection, workholding, and whether the finish allowance is locally heavy.
Test Entry and Exit as Separate Variables
Exit behavior deserves its own observation. A cutter can spring into the wall as load falls, or the path can leave a small uncut cusp when it departs too early. Compare the entry and exit under the same light and direction markings; do not average two different defects into one CAM adjustment.
Release a Repeatable Edge Strategy
A valid correction must survive repetition at more than one start point or part orientation. Preserve the original and revised toolpath, tool projection, allowance, direction, and wall measurements. If the improvement follows only one stock location, the apparent lead fix may be hiding a flatness or holding problem.
