If you've ever received laser-cut parts that were a fraction of a millimetre smaller than you drew them, or a hole that came out just slightly larger than the bolt it was meant for, you've met laser cutting kerf. Kerf is one of those details that rarely gets explained until it causes a fitment problem — and for South African engineers, fabricators and makers designing parts for online laser cutting, understanding it upfront saves a re-cut and a delay. This guide covers what kerf actually is, how wide it typically runs on mild steel, stainless steel and aluminium, and exactly how to design your DXF file so kerf never catches you out.
What Is Kerf in Laser Cutting?
Kerf is the width of material physically removed by the laser beam as it cuts through your sheet. A fibre laser doesn't cut along an infinitely thin line — the focused beam vaporises and melts a narrow channel of metal, and that channel has real width. The result is straightforward but easy to overlook: your finished outline ends up slightly smaller than what you drew, because material was removed from the edge, while any internal hole or slot ends up slightly larger, because material was removed from inside the boundary you drew.
This isn't a defect or an error in the cutting process — it's a physical property of how laser cutting works, and it applies to every laser cutter, on every material, at every thickness. The question isn't whether kerf exists, it's whether your DXF file and your cutting supplier account for it correctly.
How Wide Is a Laser Cutting Kerf?
Kerf width depends mainly on material type and thickness, plus the specific laser settings used. On a modern fibre laser — the type used for most sheet metal work in South Africa — typical kerf widths look like this:
| Material | Thickness | Typical kerf |
|---|---|---|
| Mild steel | 1-3mm | ~0.10-0.15mm |
| Mild steel | 6-10mm | ~0.20-0.30mm |
| Stainless steel | 1-3mm | ~0.10-0.15mm |
| Stainless steel | 6mm+ | ~0.20-0.25mm |
| Aluminium | 1-5mm | ~0.15-0.25mm |
These figures are typical ranges rather than fixed constants — actual kerf shifts slightly with laser power, cutting speed, assist gas and nozzle condition. But as a rule of thumb: thicker material means wider kerf, because the beam needs a larger channel to fully pierce and eject molten metal through the full depth of the sheet.
Why Kerf Matters for Your Design
For a simple flat bracket or panel, kerf rarely matters — a part that's 0.15mm smaller than drawn is invisible to the eye and irrelevant to function. Kerf becomes important in three specific situations.
Holes and fastener clearance
A hole drawn at exactly 6.00mm to fit an M6 bolt will actually cut slightly larger than 6.00mm, because kerf removes material from inside the hole boundary. For most fastener holes this generous clearance is welcome. But for press-fit bushings, dowel pins or bearings that need a tight tolerance fit, you need to know the kerf is working in your favour (or against you) and design the nominal hole size accordingly.
Interlocking tabs and slots
Tab-and-slot joints — common in enclosures, jigs and sheet metal assemblies — are the classic place kerf causes headaches. A tab cut to the exact width of its matching slot will come out slightly narrower than the slot (because kerf shrinks the tab) while the slot comes out slightly wider (because kerf enlarges it). Combined, that's roughly double the kerf width in extra clearance, which can leave joints loose. Understanding this lets you decide whether to add a compensating interference allowance for a snugger fit.
Nested parts on the same sheet
When you're packing multiple parts closely together to save material — see our guide on how to nest parts in your DXF — kerf determines the minimum safe spacing between adjacent cut lines. Too little spacing and heat from adjacent cuts can distort your parts; the general guideline is to leave a gap of at least 2-3x the sheet thickness, or a minimum of around 2-3mm on thin material.
If a feature needs to slide, press-fit, or interlock with another part, add or subtract roughly 0.1-0.2mm of clearance in your DXF to account for kerf. If it's just a mounting hole or an outer profile, don't worry about it — QuickCut's laser automatically compensates so your finished dimensions match your drawing.
How to Compensate for Kerf in Your DXF
Most CAM software and modern laser cutting systems, including the process QuickCut uses, apply automatic kerf compensation — the machine offsets its cutting path outward on external profiles and inward on internal holes, so your final part matches your drawn dimensions as closely as the machine's accuracy allows. That means for the vast majority of parts, you can draw true-to-size dimensions and trust the finished part to match.
- Draw your part at its true, intended finished dimensions — don't try to manually offset every line for kerf.
- For tight-tolerance holes (press fits, bearings, dowels), check the required fit class and adjust the nominal hole diameter by roughly half the expected kerf width if a snug fit is critical.
- For interlocking tabs and slots, add a small interference allowance (around 0.1mm per side) if you want a tight friction fit rather than a loose slip fit.
- Leave adequate spacing between nested parts — at least 2-3x material thickness — to prevent heat distortion affecting kerf consistency.
- When in doubt, order a single test part first. With no minimum order at QuickCut, this costs almost nothing and confirms fitment before you commit to a full production run.
Kerf vs Tolerance: What's the Difference?
Kerf and tolerance are related but not the same thing. Kerf is specifically the width of material removed by the cut. Tolerance is the broader, overall dimensional accuracy of your finished part — how close the real-world part comes to your drawn dimensions once you account for kerf, thermal expansion during cutting, and the mechanical accuracy of the laser itself. For a full breakdown of achievable accuracy on fibre laser cutting, see our guide to laser cutting tolerances in South Africa.
Does Kerf Affect Price?
Kerf itself isn't a separate line item on your quote. What it does influence is cut length and material efficiency on tightly nested layouts — slightly wider kerf on thicker material means marginally more total material converted to cutting waste across a sheet. In practice this is a small factor compared to material cost, thickness and total cut length. QuickCut's instant online quoting tool already factors kerf into its pricing engine, so when you upload your DXF you get an accurate, ready-to-pay price immediately — no back-and-forth with a sales rep to clarify tolerances or fit.
That's the advantage of an instant-price laser cutting service: you don't need to be a laser cutting engineer to get parts that fit. Upload your DXF, get your price in seconds, and if you've got a tight-fit feature, add a small clearance allowance using the guidance above. No minimum order means you can always test-fit one part before committing to a full batch, delivered anywhere in South Africa.
Frequently Asked Questions
Kerf is the width of material the laser beam removes as it cuts. It's the narrow channel of vaporised and melted metal left behind the cutting head, and it means your finished part is always very slightly smaller than the outline drawn in your DXF file, while any hole or slot you cut is always very slightly larger.
On a modern fibre laser, kerf typically ranges from about 0.1mm to 0.3mm depending on material and thickness. Thin mild steel and stainless steel usually cut with a kerf around 0.1-0.15mm, while thicker material or aluminium can run closer to 0.2-0.3mm.
Kerf itself doesn't directly change your price, but it does affect cut length and nesting efficiency on tightly packed layouts, which can influence cost. QuickCut's instant online quote automatically accounts for kerf when calculating your price, so you don't need to factor it in yourself.
For most parts you don't need to do anything — QuickCut's laser automatically applies kerf compensation so your finished dimensions match your drawing. For tight-fitting holes, press-fit bosses or interlocking tabs and slots, it helps to add a small clearance allowance of around 0.1-0.2mm in your DXF so parts still assemble smoothly after cutting.
Yes. Thicker material generally requires a wider kerf because the laser needs a bigger channel to fully pierce and eject molten metal through the full depth of the sheet. A 1mm sheet and a 10mm plate cut with the same laser will not have identical kerf widths.
Kerf is the width of material removed by the cut itself. Tolerance is the overall dimensional accuracy of the finished part — how close the real part comes to your drawn dimensions, accounting for kerf, thermal effects and machine accuracy. Kerf is one of several factors that make up your final tolerance.
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