Key takeaways
- Common-line nesting three 400 x 250 mm parts across a 1,250 mm sheet gives 21 parts where a 5 mm web gives 18, and cuts 19,400 mm of contour instead of 27,000 mm, a 28% reduction.
- A shared edge splits the 0.3 mm kerf between two parts, so each part loses 0.15 mm on that edge; that is inside a ±0.5 mm tolerance but outside a ±0.1 mm one.
- Every 1% of yield on a 1,250 x 2,500 mm sheet of 2 mm CRCA is 0.49 kg of steel, so a nest rule that gains 3% pays back more than a speed setting.
- Parts from one assembly must be nested in one orientation, because rotating a part 90° changes its bend line relative to the rolling direction and with it the springback.
Two nests of the same 400 × 350 mm bracket, on the same 1,250 × 2,500 mm sheet of 2 mm CRCA, produce 18 parts and 21 parts. The second one also cuts 19,400 mm of contour instead of 27,000 mm. Nothing changed in the machine, the material or the drawing; one rule in the laser nesting software changed.
Most of the difference between a good nest and a merely full one is decided by half a dozen settings that the optimiser will not choose for you. Web width, shared edges, lead-in geometry, the order cuts run in, the grain lock and what happens to the remnant. This article puts numbers on each, shows where the rules collide, and sets out what the drawing has to say for the software to be allowed to use them.
The laser cutting and fabrication hub holds the rest of this cluster.
Laser nesting software rules start with the web
The minimum gap between two parts is set by the kerf and the thickness, and the usual failure is a nest that is visually tight but has no room for the slag that comes out of the cut.
A fibre laser cutting 2 mm mild steel runs a kerf of about 0.3 mm. The cut does not just remove 0.3 mm of material; it ejects molten metal downward and slightly outward, and that spray needs somewhere to land that is not the next part's edge. A gap of 1.5 times the kerf, or 0.45 mm on this job, is the theoretical minimum and useless in practice because it leaves no room for sheet flatness, for the part shifting as it is cut free, or for the head to move between contours.
The working rule is a web of at least 0.25 times the thickness, with a floor of 2 mm. On 2 mm sheet that is 2 mm, on 6 mm sheet 2 mm, and on 12 mm sheet 3 mm. Above the floor, add width wherever the part has a long straight edge, because a narrow web between two long parallel cuts is the first thing to fail when the sheet is not flat.
Common-line cutting: the arithmetic and the catch
Common-line cutting shares one cut between two adjacent parts instead of cutting two contours with a web between them. The yield and time gains are large enough that the rule is worth setting globally, with the tolerance check as the gate.
Take the worked example. A 400 × 350 mm part, 2 mm CRCA, on a 1,250 × 2,500 mm sheet:
- With a 5 mm web, the pitch is 405 × 355 mm. Three parts fit across the 1,250 mm width and six along the 2,500 mm length, so 18 parts. Cut length is 18 × 1,500 mm of perimeter, 27,000 mm, plus the pierces.
- Common-line, the pitch is 400 × 350 mm. Three across and seven along, so 21 parts. The shared edges mean four vertical lines at 2,450 mm and eight horizontal lines at 1,200 mm, which is 19,400 mm of cut.
That is 17% more parts from the same sheet and 28% less cut. On a job running a thousand sheets a month the difference is 3,000 parts and a machine time saving that shows up in the delivery dates, not just the material bill.
The catch is tolerance, and it is a line in the kerf compensation rather than a machine setting. When two parts share a cut, the kerf sits on the nominal boundary and each part loses half of it. A 0.3 mm kerf removes 0.15 mm from each side, so the 400 mm width becomes 399.85 mm on the shared edge. Against a ±0.5 mm general tolerance that is invisible. Against a ±0.1 mm tolerance on a mating edge it fails, and the software will not know unless the tolerance is entered against the contour.
The second catch is fit. A shared edge between a panel and a door leaves both with a cut edge that matches the other exactly, which is fine until the parts are coated: 80 µm of powder on each edge takes 0.16 mm out of the 0.3 mm gap, and a door that closed on bare steel binds once it is painted. Where two parts must fit together after coating, keep them apart on the nest.
The rules that decide edge quality rather than yield
Lead-ins, lead-outs and pierce points
A pierce is a hole before it is a cut. The beam sits at one point and drills through, and on 3 mm mild steel that takes about 0.4 s and leaves a crater roughly 1.5 kerf widths across with a raised rim. Start the contour from inside that crater and the finished edge carries the mark.
Place the pierce at least 2 mm clear of the finished contour on thickness up to 3 mm, and 3 mm above that, either on scrap or on a sacrificial tab. Lead in along the contour for 1.5 to 2 times the thickness, minimum 2 mm, with an arc lead-in on stainless and aluminium because a straight lead-in leaves a visible witness at the start point on a brushed finish.
Cut order and heat
Every cut puts heat into the sheet, and the sheet has nowhere to send it except the surrounding metal. A part nested between other parts is surrounded by hot material, and its cut runs hotter than a part on the sheet edge. On thin sheet that shows as a wider kerf, more dross on the last third of the contour, and a skeleton that warps enough to lift a corner off the bed.
Common-line nesting makes this worse because a shared edge is a long continuous cut. A 2,500 mm run along the sheet in 2 mm CRCA at a typical 25 m/min takes 6 s, and the beam does not stop putting heat in. Three mitigations matter: cut inner features before the outer contour, segment long shared lines into 500–800 mm runs, and order the parts so the beam works from the inside of the nest outward rather than sweeping back and forth across hot metal.
Micro-joints
A part that is fully cut free before the cut is finished can tip up, and a tipped part hits the head. Micro-joints, 0.3–0.8 mm of uncut material, hold the part in place until the sheet leaves the bed. Use two per small part and four on anything over 500 mm on a side, placed away from a finished edge that will be seen. The cost is a break-off burr at each joint, which is the same burr the hand tools already remove.
Grain and orientation
Cold-reduced sheet has a rolling direction, and its bendability and springback both depend on the angle between the bend line and that direction. ISO 3574 defines the grades and the mechanical properties that go with them, but not the direction of the grain on your nest; that is a drawing decision.
If the optimiser is free to rotate a bracket 90° to fill a gap, it changes the bend line from transverse to parallel to the rolling direction. On a tight radius that is the difference between a clean bend and a crack; on a comfortable radius it is a few tenths of a degree of springback difference between two parts that are supposed to be identical. Lock the orientation on the nest for any part that is formed, and lock all parts of the same assembly to the same orientation so the batch is consistent.
Where the rules collide, and which one wins
The rules fight each other on real jobs, and the order of precedence is what turns a rule list into a decision.
| Nesting rule | Typical setting | What it changes | Ganesh limit or note |
|---|---|---|---|
| Web between parts | 0.25 t, floor 2 mm | Part count, dross, handling | 2 mm minimum on any sheet we cut; 3 mm above 6 mm |
| Common-line cutting | Shared edge where tolerance allows | Yield, cut length, half-kerf per edge | Allowed where the 0.15 mm loss sits inside the contour tolerance |
| Kerf compensation | 0.3 mm at 2 mm CRCA | Part size, shared edges, hole size | Applied per thickness, not per job |
| Pierce offset | 2 mm to 3 mm from contour | Edge mark, dross at start | Pierce on scrap or a tab on visible faces |
| Lead-in | 1.5–2 t, minimum 2 mm | Witness mark, edge quality | Arc lead-in on stainless and aluminium |
| Micro-joints | 0.3–0.8 mm, 2–4 per part | Tip-up, head crash, break-off burr | Required on any part with a cut-out island |
| Grain lock | Fixed orientation per assembly | Springback consistency, cracking | Set on the drawing, not left to the optimiser |
| Remnant | Keep above 300 mm × 300 mm | Material reuse, scrap value | Remnants labelled by grade and thickness, never mixed |
| Cut order | Inner first, edge-in | Heat, dross, skeleton warp | Long shared lines segmented into 500–800 mm runs |
The precedence is: tolerance first, then grain, then heat, then yield. That order is uncomfortable for anyone measuring a nest by utilisation, because it means accepting a lower percentage to hold a dimension. The alternative is a nest that reports 92% and ships parts that fail at the brake.
Yield, time and the number that matters
Utilisation is the headline number and the least useful on its own. What a buyer actually pays for is material consumed per good part, and that has three components: nest yield, cut length and scrap rate at the next operation.
On the 1,250 × 2,500 mm sheet of 2 mm CRCA, 1% of the area is 31,250 mm², and at 7.85 g/cm³ that is 0.49 kg. A rule change that gains 3% on a thousand sheets a month saves 1.47 tonnes of steel, which is a number a procurement engineer can take to a review without any price assumptions attached.
Cut length behaves differently. Twenty-one parts cut as separate contours would take 31,500 mm; common-line takes 19,400 mm, so the 12,100 mm removed is 38% of the travel, and at a 25 m/min feed it is 29 s less cutting per sheet. Add the pierce count reduction and the sheet handling is the same, so the saving lands directly in the rate per part.
The trap is chasing utilisation with a nest that adds heat. A nest that packs parts 1.5 mm apart and runs one long common line can show 94% and still produce drossed edges that need a second operation, and the second operation costs more than the 2% of material it saved. The measured trade is in the edge quality by thickness limits, which set the cut quality class an edge has to meet before the nest is judged good.
What Ganesh runs, and how a nest is signed off
Ganesh cuts on a 12 kW fibre laser with a 40 ft × 16 ft bed, 12.2 m by 4.9 m, supported by two 6 kW and two 3 kW machines. That bed takes a full sheet of any standard size plus the remnant of the last job, which is where most of the yield gains on long work actually come from: the large-format cutting article covers what the bed length makes possible. The laser cutting capability sets out materials and thicknesses, from mild steel and CRCA through stainless, aluminium, brass and copper, to 20 mm plate on the laser and 30–40 mm on the iron worker for plate work.
Every nest is checked against the drawing set before it runs: tolerance against common-line edges, grain lock on formed parts, pierce positions on visible faces, and remnant labelling by grade. The first sheet off a new nest is inspected against the drawing, which is the same first article inspection used on the first-off of a formed part, and the result is filed with the job. Where a nest is revised mid-order because a remnant is used, the revision is recorded against the job rather than left as a change in the machine.
We do not run a tube laser or a 5-axis head, so a part that needs holes in a formed wall is cut flat and pierced later, and the nest has to leave the material for that operation.
What to put on the drawing, and what to leave to the nest
The drawing decides how much freedom the software has. Six notes are enough.
- Material grade and rolling direction, where a formed edge is close to the minimum radius.
- A rotation lock, stated as "do not rotate" on any part whose bend quality depends on grain direction.
- Tolerance per contour, so the nest can decide whether a shared edge is allowed.
- A finished-edge note, meaning the edges that must meet ISO 9013 class 2 or better, so pierce and lead-in positions avoid them.
- The coating condition, because two parts that fit before coating may not fit after 80 µm of powder.
- The quantity basis: per sheet, per set or per month, since the nest that suits a one-off is not the nest that suits a recurring order.
Everything else belongs to the nesting software, and leaving it there is the point. A drawing that specifies a web or a nest layout removes the flexibility the job needs when a remnant arrives in a different size.
Send the part list, the material and the monthly quantity, and the engineering team will tell you which parts should run together and where the tolerance forces them apart. A quotation request with the drawing set attached is the fastest way to start.
Frequently asked questions
What part spacing should I allow between laser-cut parts?
At least 1.5 times the kerf and at least 0.25 times the material thickness, with a working floor of 2 mm for handling and slag clearance. On 3 mm CRCA that is 2 mm rather than the 1 mm that looks tight enough in the preview.
Does common-line cutting make parts undersize?
It splits the kerf. A 0.3 mm kerf centred on a shared edge takes 0.15 mm off each part, so a 400 mm width becomes 399.85 mm. That is fine against a ±0.5 mm tolerance and not fine against a ±0.1 mm one.
Why do parts at the end of a long common line have dross?
Heat accumulates as the cut runs, the kerb widens, melt ejection falls behind the beam and the last section drosses. Segmenting the cut and cutting inner features first spreads the heat over the sheet.
Can nesting software rotate parts to improve yield?
Only if the drawing allows it. Rotation changes the bend line relative to the rolling direction, which changes springback, and on a formed part that shows as an angle difference between components of the same assembly.
How much does 1% yield actually save?
On a 1,250 x 2,500 mm sheet of 2 mm CRCA, 1% of the sheet area is 31,250 mm², which at 2 mm thickness and 7.85 g/cm³ is 0.49 kg of steel. Over 1,000 sheets a 3% gain is 1.47 tonnes.
Sources and further reading
- ISO 9013 — Thermal cutting: classification of thermal cuts, geometrical product specification and quality tolerances, which defines the cut quality classes used on an edge · reviewed 3 Nov 2026
- ISO 3574 — Cold-reduced carbon steel sheet of commercial and drawing qualities, the basis for the bendability and rolling direction behaviour · reviewed 3 Nov 2026
- Bureau of Indian Standards — IS 513 cold reduced carbon steel sheet and strip, the grade and thickness tolerance reference used for CRCA nests · reviewed 3 Nov 2026
Send the part list and the annual quantity
Include the drawing set, material, thickness and monthly volume. We will tell you which parts nest together, where the grain lock falls and what the yield does to the piece price.
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