Layers & Path Rules — Deep Dive

How to use CAD layers and SheetCam rules to control tools, speeds, and behavior without hand‑editing every feature.

1) What “Layers” mean in SheetCam

• Layers come from CAD (DXF/SVG/DWG). Keep them when importing.

• In Operations → Plasma cutting (or Router ops), you can target one or more layers so that each operation applies only to those entities.

• Think of layers as buckets of geometry that share the same cut intent (tool, speed, offset, rules).

Suggested plasma layer scheme (simple & effective)

• OUTER – Perimeters/outer profiles → Cut path = Outside.

• HOLES – Normal internal holes/slots → Cut path = Inside.

• TINY_HOLES – Small holes (e.g., ≤ 12 mm / 0.5 in) → special slow/THC‑off rules.

• MARK – Etch/mark lines → Cut path = On with low‑power tool/marking settings.

• SLOTS – Narrow slots that need different leads or speeds.

Tip: Keep names uppercase & short. Consistency pays off when building operations and templates.

2) Building operations by layer

1. Operations → New operation → Plasma cutting.

2. Set Tool (your amperage/material tool), Cut path (Inside/Outside/On).

3. In Layers, pick exactly the layer(s) you want this op to control.

4. Set default Leads and Direction (CW/CCW) for that layer.

5. (Optional) Open Rules to add size‑based behavior (see below).

6. OK. Repeat for each layer bucket (e.g., one op for TINY_HOLES, another for OUTER).

Ordering: In the operations list, cut internals before externals. Use “Move up/down” or the automatic order + tweak.

3) Path Rules: what they do

Path Rules let SheetCam override speeds, THC, leads, and other parameters when specific conditions are met. They are defined inside an operation and applied to the contours that op controls.

Common rule triggers

• Hole diameter below X (applies to closed internal profiles).

• Open contour shorter than Y (good for tiny slots or marks).

• Arc/radius below R (tight corners / small arcs).

• On specific layer(s) (layer‑scoped rules if desired).

Common rule actions

• Feed rate change (e.g., 30–60% for small holes).

• Disable THC while cutting tiny holes or during lead‑in/out.

• Override lead‑in/out type/length (e.g., straight lead‑in on small holes, no lead‑out).

• Overcut / endpoint extension (posts may support adding a little tail on exit).

Exact names/options vary by post & SheetCam version. Use the Rules tab of the operation to preview what the rule will affect (start with conservative values).

4) Ready‑made rule recipes (plasma)

A) Small holes (≤ 0.5 in / 12 mm)

• Trigger: Hole diameter ≤ threshold.

• Actions:

  • Feed = 35–60% of normal cut speed.

  • Disable THC within the hole.

  • Lead‑in: short straight lead (~kerf to 1.5× kerf).

  • Lead‑out: off (prevents nicks on the finished edge).

B) Tiny features / short open contours

• Trigger: Open contour length ≤ e.g., 0.75–1.00 in (20–25 mm).

• Actions: Reduce feed (e.g., 60–80%), keep THC off, consider Lead‑out off. For hairline marks move these to a MARK layer and use Cut path = On with a marking tool.

C) Tight corners / small arcs

• Trigger: Arc radius ≤ Rmin (choose a value from your cut charts where quality drops).

• Actions: Reduce feed (e.g., 70–85%), optionally disable THC in the corner range.

D) Kerf‑sensitive slots

• Put into SLOTS layer and make an operation with Cut path = Inside or On depending on target width. Add a rule on open contour length if slots are short to slow slightly and keep THC off.

5) Leads, start points, & direction

• Start points: Mode → Edit start points. Place starts away from show faces and critical corners.

• Lead‑in: Arc is forgiving for general profiles; straight is better for small holes. Length ~1–1.5× kerf is a good general start.

• Lead‑out: Often off for small holes to avoid a second mark; on perimeters a short lead‑out can improve edge finish.

• Direction (CW/CCW): Many plasma setups prefer CW for internal and CCW for external cuts (or vice‑versa) depending on swirl & post. Keep it consistent across ops.

6) Verification workflow

1. Toggle View → Show leads and Show rapids to see entries/exits.

2. Simulation: Watch pierces & feed changes. Rules should clearly slow the tool where expected.

3. Count pierces and compare with expectation; small‑hole rules shouldn’t create extra pierces.

4. If behavior looks wrong, check operation order and rule precedence (rules are evaluated within the operation they’re defined in).

7) Templates & reuse

• Save a “Plasma  – Mild Steel” job template that already contains:

  • Tools for common thicknesses.

  • Operations targeting HOLES, TINY_HOLES, OUTER, MARK.

  • Pre‑tuned rules (you can still tweak per job).

• New job = open template → File → Import drawing… → most work is already done.

8) Troubleshooting

• Rule not firing: The geometry isn’t matching the trigger (e.g., the “holes” are polylines that don’t register as closed circles). Fix in CAD or use Edit → Join.

• Wrong layer cutting: Verify the operation’s layer list. SheetCam won’t guess—if the layer isn’t selected, that op won’t touch it.

• Unexpected offsets: Ensure the Cut path (Inside/Outside/On) is correct for that layer.

• Chatter on tiny holes: Slow more, use straight lead‑in, THC off, and check pierce height/delay.

Add your shop’s exact thresholds (e.g., “tiny hole = ≤ 9 mm on 10‑ga MS”) and your preferred speeds/THC policy here so operators don’t guess.