OpenNest/docs/automatic-scrap-cutoffs.md

Automatic scrap cutoffs

Finish nesting, then choose Nest > Automatic Scrap Cutoffs (All Plates) to process the entire nest with one dialog. Plate > Automatic Scrap Cutoffs still processes only the active plate. The manual Sheet Cut-Off command remains available.

Preview and apply

1. Finish or cancel any active nesting/fill operation first, and wait for it to finish stopping; closing its progress window alone does not finish the operation. Enter the maximum strip spacing along the sheet's length. The initial value is 35 in, or 889 mm for a metric nest. This is the maximum distance between new cut lines, not the length of a cut.
2. Set Minimum strip, initially half the spacing (17.5 in or 444.5 mm). The first strip from the origin-side sheet edge and each strip between successive new lines stay between this minimum and the spacing; the last strip before the separator or sheet end can be shorter. This field follows spacing changes until you edit it. Setting it equal to spacing restores the fixed grid.
3. Set Minimum tail to keep, initially 12 in or 304.8 mm. This measures the reusable tail's length along X, after separator clearance, not its area. A shorter tail does not get a new final separator; a tail at or above the minimum can be retained. Zero allows any positive tail.
4. Opening the modal dialog previews the initial proposal. After changing a setting, choose Preview to refresh it. Cuts run across the active sheet's actual width, advancing along X from the origin-side edge in the plate's quadrant. A bold green or red status line states what Apply will do; the occupied span, used span, separator X, retained tail, and strip cut length versus the fixed grid appear as measurements. The details list reports only issues and notices. The sheet cannot be edited while the dialog is open.
5. Choose Apply (or Apply to All Plates) to recalculate against the current parts/settings and add ordinary cutoff definitions at the end of each plate's cutting sequence. Blocked or empty proposals add nothing. Existing parts and manual cutoff definitions are not moved or reordered. Cancel, Escape, and closing the dialog discard the detached preview.

For the Nest command, the on-sheet overlay and upper measurements show the active plate; a per-plate table lists each plate's proposed cut-off count, occupied and used spans, retained tail, and readiness (Ready, Blocked, or No change), while the details list reports only issues and notices, each prefixed with its plate number. Each plate uses its own dimensions, quadrant and part spacing with the dialog's common spacing/minimum-strip/minimum-tail settings and current cutoff clearance/direction settings. No plate navigation or per-plate confirmation is required. Empty or unchanged plates are left untouched. A blocking conflict or invalid plate prevents changes to all plates, with the plate number reported; resolve it before retrying. If application fails after changes begin, all touched plates' original cutoff programs and sequence are restored. An explicit incomplete-recovery warning requires manual review before saving or cutting.

An empty sheet is left untouched. Invalid input or out-of-sheet part geometry prevents automatic planning. Excessively small spacing is rejected rather than allocating an unbounded number of cuts. Small bounded discrepancies between converted material and cached bounds—including amplified roundoff in fitted near-tangent arcs—are accepted without changing the part or its program. The same conservative numerical padding applies to cutoff pruning and exclusions. Their broad-phase envelope uses the farther edge of the cached box and converted perimeter; a cutoff within the narrow uncertainty band at a cached edge gets a full-envelope exclusion instead of relying on a near-tangent contour intersection. Elsewhere the contour is retained for precise trimming. Larger arc-center discrepancies still prevent automatic planning rather than risking a cut through material; repair the geometry before retrying.

Preserving the unused tail

A proposed tail shorter than Minimum tail to keep is left attached to the scrap skeleton by omitting only the final separator. The nominal skeleton grid is not extended into that tail, and no retained tail is claimed. Existing cutoff definitions—including an end cutoff from an earlier run—are never removed by this setting.

Only real parts contribute to the occupied envelope; existing cutoff parts do not. When there is room, the final separator is beyond the furthest occupied extent by the larger of plate part spacing and cutoff part clearance, plus numerical tolerance. Repeated skeleton cuts stop before that separator. The larger margin affects only the separator: repeated cuts keep the existing manual-cutoff clearance behavior.

Cutoff trimming measures clearance from the part contour, excluding tagged lead-in and lead-out moves when building the closed outline. Leads must not turn a recessed outline into a convex hull and leave oversized gaps elsewhere. Genuinely open contours still use the conservative hull/bounds fallback. The conservative curve/offset approximation can leave a small extra gap (about 0.0003 in on a straight edge at the default 0.02-in clearance), not an extra quarter inch.

If no safe separator fits inside the sheet, there is no retained-tail claim and the nominal cuts may cover the full sheet length. A proposed tail is not reported as separated unless its generated program spans the full sheet width. An active clamp blocks any proposed full-width line whose X coordinate falls in the clamp's whole footprint plus bottom-edge clearance, including a nominal grid line or an equivalent existing line. A tolerance-close existing line is tested at its own X as well as the proposed X, because that existing line is what would be certified. A same-line manual cut with different limits still blocks the whole plan, even on a clamp. Blocked lines are skipped with a clamp diagnostic; a blocked tail also reports NoSafeTailSeparator rather than claiming separation. Removed clamps on a sheet are absent from its active zones and do not block cuts. Stored zones are relative to the sheet's lower-left corner; the planner maps them into the plate's quadrant frame (the same frame as part and cut-off coordinates) before comparing, so the rule holds in all four quadrants. Obstructed or minimum-length-filtered lines produce diagnostics; they are not proof of a completed partition.

For a 120-by-81-inch sheet whose parts extend through 80 inches, the fixed grid would put skeleton lines at 35 and 70 inches, followed by a separator beyond 80 inches at the required margin. With a 17.5-inch minimum strip, the planner can move those two lines toward the origin to shorten their trimmed cut segments. The separator does not move, and there is no line at 105 inches through the retained tail.

Shifting strip lines

The preview searches line positions together to minimize the total emitted strip-line cutting length after part clearance and minimum-segment filtering. Equal lengths favor fewer pierces, then less total movement from the fixed grid. The number of new lines in each span stays at the fixed-grid count; it never adds cuts to chase a shorter path. For example, a part edge at 34.75 inches can make a 35-inch line run beside much of the part, while a small shift toward the origin lets that line cross the part and skip its material. The preview reports the measured strip-cut length and the corresponding fixed-grid length, including when Minimum strip equals spacing; a ShiftedCut notice identifies moved lines. Because the lines are optimized together, an individual line can cut slightly more while the total falls; its notice reports that local increase rather than a negative saving.

Existing full-width vertical cut-offs inside the used span become fixed strip boundaries; the planner fills only gaps longer than the spacing, never moving or duplicating the manual cut. A partial manual cut is not a boundary and its position is avoided. Active clamps exclude candidate positions including bottom-edge clearance. If a gap cannot place all its lines outside clamps, it falls back to nominal lines and reports any blocked cuts under the existing guard. An unchanged rerun adds nothing. The desktop defaults to shifting; API callers that omit MinimumStripLength retain the fixed-grid behavior.

Limits and operator review

View > Draw Rapids follows the complete cutting sequence: an incoming rapid ends at a cutoff's first pierce, gaps between its trimmed segments remain rapids, and the next part's rapid starts at the cutoff's final cutting endpoint—not its last pierce. This display does not add a return move or alter the cutoff program.

• Maximum strip spacing is not a disconnected-scrap guarantee. Clearance gaps and suppressed short segments can leave bridges between scrap regions. This command does not certify that every connected scrap piece is disconnected or fits a hopper.
• The active sheet's physical width is used, not a hard-coded 81 inches. Check the actual width against the hopper; a wider sheet is not automatically hopper-compatible.
• Internal-hole scrap is not processed. This command reuses the outside-skeleton behavior of manual cutoffs; it does not force cuts through parts or remove clearance to guarantee separation.
• Review the preview and posted NC using the normal machine-review process before production cutting.

Part sequencing

For Plate > Sequence Parts > Manual Sequence, choose the one-based sequence number and hover a part on the sheet; only the part under the pointer is outlined. Click it to place it at that exact position, then the number advances up to the last part. Clicking empty sheet space changes nothing. Use Done, the window close button, right-click on the sheet, or Escape to leave the tool. Manual reordering changes neither geometry nor quantities.

After adding cutoffs, apply Part Sequencing to the current plate or all plates. Each cutoff is moved earlier as needed so it is cut before every part its nominal line passes through. Ordinary parts retain their relative order from the chosen sequencing route. A cutoff that splits the whole sheet — one continuous cut from sheet edge to sheet edge, such as a tail separator — goes after every part and every other cutoff, so the head never travels back across the separated edge. Cutoffs that cross no part but leave gaps keep their normal route position. Cutoff geometry, clearance, part programs, placements, and quantities are unchanged.

The dependency check uses the nominal horizontal/vertical line and its start/end limits, not the trimmed cutting segments, which intentionally skip the parts. It conservatively checks placed part bounds (including edge contacts), so a cutoff through a concave recess can also move ahead of that part. Definitions are matched by drawing identity, not their displayed names. A cutoff part with no matching definition is conservatively ordered before all ordinary parts.

This rule runs when applying automatic sequencing, after reversing the exit-first sequencer route into cutting order. Manual sequence edits are still manual; adding or moving cutoffs does not automatically reapply this rule. Reapply Part Sequencing after layout changes and review the resulting rapids before posting. Regeneration and saving/reloading retain the applied mixed sequence.

The all-plates command uses PlateSequencing.ApplyAll, which snapshots the target plate references before sequencing. Reordering parts raises collection events that can replace the nest's trailing empty plate; those events must not invalidate the batch's iteration or skip any original plate. This snapshot is not a transaction or a concurrency guard: sequencing still runs synchronously on the owning thread, using the same per-plate cutoff rules.

Rerunning, editing, and saving

The command is one-shot; spacing, minimum-strip and minimum-tail inputs start at their defaults each time the dialog opens. Generated lines are ordinary cutoffs and can subsequently be dragged, deleted, or sequenced with the existing tools. Moving parts regenerates their trimmed segments but does not reposition the saved cut-off lines or recalculate the retained tail automatically.

Rerunning unchanged suppresses equivalent existing full-span lines. A limited cutoff at a proposed line is a conflict requiring manual review, not permission to replace it or add overlapping NC moves. Existing definitions are never silently deleted or expanded.

Saving .nest retains ordinary cutoff positions, axes, limits, and sequence. Loading regenerates cutoff programs using the reader's default cutoff settings; exact toolpaths made with nondefault cutoff settings are not guaranteed to round-trip. Review regenerated paths before posting.

Implementation boundary

AutomaticCutOffPlanner in Core builds detached definitions and diagnostics without changing the input plate. AutomaticCutOffOptions.MinimumTailLength is a finite, nonnegative distance in model units; its programmatic default of zero preserves the previous behavior, while the desktop explicitly supplies its unit-aware 12-in / 304.8-mm default. AutomaticCutOffBatch.Create plans an ordered plate list, and Apply replans the complete list before mutating any plate, refusing a blocked batch and recovering touched cutoff state on exceptions. Callers must prevent concurrent edits throughout planning/apply. The desktop dialog renders the active plate's detached preview through PlateView.SetActiveParts; both menu commands apply through the shared batch service, which adds definitions to Plate.CutOffs and uses Plate.RegenerateCutOffs. It must not accept preview parts directly, because doing so would bypass cutoff persistence and regeneration. There are no new nesting, post-processing, or .nest format rules.