Laser Cut Tolerances Explained: Kerf, Taper and the Print

How a laser tolerance class is stated

ISO 9013 is the international standard for thermal cutting by oxyfuel flame, plasma or laser. It classifies a cut by the quality of the cut surface, measured as a perpendicularity or angularity tolerance and as the mean height of the profile, and it gives dimensional tolerances, with a separate case for parts finished after cutting and a machining allowance for them (source 1). It applies when a drawing or order refers to it, so a print that wants an ISO 9013 class has to name one. For any cut edge on laser-cut parts, the tolerance on the quote is the one that governs.

Read the fine print with any laser tolerance. ISO 9013 defines kerf width at the upper edge of the cut and lists the top kerf width and the bottom kerf width as separate quantities, so the kerf at the top and at the bottom of a cut can differ (source 1). It defines the perpendicularity or angularity tolerance as the distance between two parallel lines that the cut surface profile fits between, and notes that it includes flatness deviations of the cut surface (source 1). A print that cares which face a dimension is measured on says so. Sheet thickness is a separate tolerance: rolling leaves sheet thinner at the edges, and Wikipedia’s sheet metal article carries thickness tolerance tables for steel, aluminum and stainless (source 6). The cut does not change it, and a thickness tighter than the sheet carries is a machined face, not a cut.

Kerf, piercing and small holes

Kerf is the width of material the cut removes. ISO 9013 measures it at the upper edge of the cut (source 1), and Wikipedia’s kerf article says the kerf a laser leaves changes with the laser’s power and the material being cut (source 2). Wikipedia’s laser cutting article gives kerf widths as small as 0.004 in (0.10 mm), depending on material thickness (source 3). Send the part drawn at its finished size, not offset for kerf; what file to send for laser cutting covers the file. A slot narrower than the kerf cannot be cut at all.

Every hole and slot inside a profile starts with a pierce. Wikipedia describes piercing as usually done slowly with a pulsed beam to prevent cut edge damage or an inconsistent kerf width (source 3). A small hole in thick plate that has to fit something goes on the print with its finished size and tolerance; the quote says whether the cut holds it or it is finished after cutting.

Edge taper, heat-affected zone and dross

A laser edge is not perfectly square. ISO 9013 measures squareness as the perpendicularity or angularity tolerance and roughness as the mean height of the profile, two separate characteristics, and it names the lines left on the cut surface drag lines (source 1). Both matter when an edge is a bearing or locating surface: call it out on the print, and the quote says how that edge is finished after cutting. It is then inspected against the print.

The heat-affected zone is the area of base material that is not melted but has had its microstructure and properties altered by welding or heat-intensive cutting (source 4). Wikipedia says laser systems have a small heat-affected zone (source 3). A tapped hole is called out by its thread on the print, not as a cut hole size, and is quoted as its own operation after cutting. ISO 9013 defines dross as metal residue sticking to the lower part of the cut (source 1). If an edge has to be clean, write the deburr callout rather than assume it.

Tolerance on bent parts

Bending adds its own tolerances on top of the cut: bend angle, edge to bend, bend to hole or internal cut feature, the distance across a bend and the overall size of the formed part. For a bent part the quote states the tolerance used. The inside radius is quoted as drawn, with a note if it won’t form. Wikipedia’s bending article gives two reasons: residual stresses make the material spring back, so the sheet must be over-bent to reach the angle, and broadly speaking each bend is its own set-up, so the number of set-ups and the geometric changes during bending make tolerances and bending errors hard to plan ahead (source 5). A dimension that crosses two bends depends on both.

Design to the stack rather than against it. Hole-to-hole distances that matter should sit on the same flat, not across a bend. Slots that must align across a bend get an open tolerance, or a hole in one flange and a slot in the other. A formed part with a tight position requirement across a bend is a machined part, or a laser blank with the critical feature machined after forming, and the quote says which route it took and why.

Tighter than the laser class: call it out, machine it after, inspect it

When a feature needs tighter than the cut, call it out on the print and it is quoted as an operation after cutting. A dowel or press-fit hole is quoted as laser cut, then finished by reaming. Wikipedia describes precision reamers as enlarging a previously formed hole by a small amount with a high degree of accuracy, and gives -0/+0.02 mm (0.0008 in) as an example tolerance for a reamed hole (source 7). A slot width the print holds tighter than the cut is quoted as a milled feature. A locating edge with a tight callout is quoted as a ground edge; see precision grinding. The laser blank plus the machined feature is quoted as one job, described on laser cut, tapped and machined as one order, and the finished feature is inspected against its own callout on the print, not against the laser class.

Inspection follows the print: the cut profile against the tolerance on the quote, and each machined feature against its own callout. ISO 9013 states that flatness defects are not addressed as such in the standard and refers to the standards for the material (source 1), so a flatness callout on a laser-cut part is a real request and is quoted as one. Position, perpendicularity and runout callouts are quoted from the print. The same discipline for milled and turned parts is on CNC machining tolerances.

How to write tolerances on a laser print

A laser print needs one general tolerance note and a handful of specific callouts. ISO 2768-1 gives general tolerances for linear and angular dimensions that carry no individual tolerance, for parts made by metal removal or formed from sheet metal, in four classes: f fine, m medium, c coarse and v very coarse (source 8). A print applies it by writing "ISO 2768" and the class in or near the title block, for example ISO 2768-m, and the standard says a feature whose function needs a smaller tolerance should carry it individually beside the dimension (source 8). ISO 2768-1 also says that where another standard gives general tolerances for a process, the drawing refers to that standard (source 8); for thermal cuts that is ISO 9013, which has its own dimensional tolerances (source 1). So the cut dimensions take an ISO 9013 reference and the machined or formed dimensions an ISO 2768 class. Then call out only the dimensions function needs: the two mounting holes that must align with a mating part, the slot a fastener slides in, the bore that takes a bearing. Each callout tighter than the general note may need an operation after cutting, and the quote says which, so each one should earn its place on the drawing.

ASME Y14.5, Dimensioning and Tolerancing (2018 edition, reaffirmed 2024), at asme.org/codes-standards/find-codes-standards/y14-5-dimensioning-tolerancing establishes the symbols, rules and definitions for stating and interpreting GD&T (source 9). Where a hole pattern mates with another part, give it a datum edge to measure from and a position tolerance. Name the material and thickness on the print. Send the print with the DXF or STEP; what file to send covers the rest. For how laser, waterjet and milled edges differ, see laser vs waterjet vs CNC; for the stainless choice on a cut part, 304 vs 316; for the process itself, laser cutting. Upload at /quote/ and a person quotes it in 24-48 hours.

Sources

All accessed 4 October 2026. Where a figure here differs from your print, the print governs.

1. International Organization for Standardization, "ISO 9013:2017, Thermal cutting - Classification of thermal cuts - Geometrical product specification and quality tolerances", third edition, 2017-02, scope, contents and clauses 3 to 4 read from the preview copy at standards.iteh.ai/catalog/standards/sist/448296ef-3e8a-4242-875f-bc849f166ec5/iso-9013-2017 (a cut is classified by perpendicularity or angularity tolerance u and mean height of the profile Rz5, with dimensional tolerances and a machining allowance for finished parts; it applies where a drawing refers to it; kerf width is taken at the upper edge, with top and bottom kerf width as separate terms; dross is metal residue sticking to the lower part of the cut; flatness defects are not addressed as such). The standard itself is not reproduced here.

2. Wikipedia, "Kerf": en.wikipedia.org/wiki/Kerf (the kerf left behind by a laser beam can be changed based on the laser’s power and type of material being cut).

3. Wikipedia, "Laser cutting": en.wikipedia.org/wiki/Laser_cutting (kerf widths as small as 0.004 in (0.10 mm) are possible depending on material thickness; laser systems have a small heat-affected zone; piercing usually involves a high-power pulsed beam that slowly makes a hole, to prevent cut edge damage or inconsistent kerf width).

4. Wikipedia, "Heat-affected zone": en.wikipedia.org/wiki/Heat-affected_zone (the area of base material, metal or thermoplastic, which is not melted but has had its microstructure and properties altered by welding or heat-intensive cutting operations).

5. Wikipedia, "Bending (metalworking)": en.wikipedia.org/wiki/Bending_(metalworking) (residual stresses cause springback, so the sheet must be over-bent to reach the angle; broadly speaking, each bend corresponds with a set-up; the number of set-ups and the geometric changes during bending make tolerances and bending errors hard to address ahead of time).

6. Wikipedia, "Sheet metal": en.wikipedia.org/wiki/Sheet_metal (rollers bow slightly in rolling, so sheets are thinner at the edges; thickness tolerance tables for steel, aluminum and stainless steel).

7. Wikipedia, "Reamer": en.wikipedia.org/wiki/Reamer (precision reamers enlarge a previously formed hole by a small amount with a high degree of accuracy; reamed holes with tolerances of -0/+0.02 mm (0.0008 in) given as an example).

8. International Organization for Standardization, "ISO 2768-1:1989, General tolerances - Part 1: Tolerances for linear and angular dimensions without individual tolerance indications", first edition, 1989-11-15, scope, clauses 1 to 5 and annex A read from the preview copy at standards.iteh.ai/catalog/standards/sist/b6b59a87-bc2b-4a35-af9d-635a3702cfc8/iso-2768-1-1989 (four classes f, m, c, v; covers parts made by metal removal or formed from sheet metal; indicated by "ISO 2768" and the class in or near the title block, for example ISO 2768-m; a feature that needs a smaller tolerance for function is indicated individually; where other standards give general tolerances for a process, the drawing refers to them, clause 2). The standard itself is not reproduced here.

9. ASME, "Y14.5 Dimensioning and Tolerancing" (2018, reaffirmed 2024): asme.org/codes-standards/find-codes-standards/y14-5-dimensioning-tolerancing (establishes symbols, rules, definitions, requirements, defaults and recommended practices for stating and interpreting GD&T).