Laser-Cut Bolt Holes in Steel Structures: Test Against Drilling
PCL Group application engineering, Jinan · Updated 20 October 2026
Can a fiber laser replace the radial drill for bolt holes in structural steel? We put the question to a test: holes cut on a 30 kW fiber laser and holes drilled on a radial drill, in the same Q355B plate, measured against the same acceptance criteria. The laser holes passed on every thickness we tried. This report sets out how the test was run, what was measured, what the standards say, and where drilling is still the safer choice.
Findings in brief
- Plates: Q355B at 12, 16, 20 and 30 mm.
- Diameter deviation of laser holes was in the same range as drilled holes and inside the Class C tolerance.
- Spacing between adjacent holes stayed within ±1.0 mm.
- The laser-cut hole wall was smoother than the drilled wall, with no exit burr.
- Edge hardness (HV10) was higher than on drilled holes, but below the 350 HV limit applied to the heat-affected zone.
On this page
What the codes allow
For a long time, structural codes treated thermally cut bolt holes with suspicion, because flame-cut holes were rough, out of round and hard at the edge. Fiber lasers changed the picture, and the codes have moved with them. Before switching, check which code governs your project and which edition it refers to.
| Code | What it says about cut holes | Key figures |
|---|---|---|
| GB 50205-2020 (China) | Sets acceptance tolerances for fabricated bolt holes | Class C holes: diameter +1.0 / 0 mm; wall roughness Ra ≤ 25 µm |
| GB 50017-2017 (China) | Sets standard hole sizes for high-strength bolted joints | M16: 17.5 mm, M20: 22 mm, M24: 26 mm, M30: 33 mm |
| AISC 360 (USA), 2016 and later | Thermally cut bolt holes are permitted | Surface roughness ≤ 25 µm (1,000 µin); gouges ≤ 1.6 mm (1/16 in) |
| EN 1090-2 (Europe) | Thermal cutting is permitted where the cut-edge hardness limit is met | Hardness limit for grades up to S460 is 380 HV10 |
Hole position matters as much as hole size. GB 50205 allows ±1.0 mm between any two holes in the same group up to 500 mm apart, and ±1.5 mm from 501 to 1,200 mm. Between the end holes of adjacent groups the allowance widens with distance, from ±1.5 mm up to ±3.0 mm over 3 m.
Test method
- Material
- Q355B plate
- Thickness
- 12, 16, 20, 30 mm
- Laser
- 30 kW fiber
- Drill
- Z3080×25 radial
- Hole class
- Class C
- Criteria
- GB 50205-2020, GB 50755-2012
Each plate was cut on the laser and drilled on the radial drill with the same hole pattern, so the two sets could be compared hole for hole. We measured diameter, spacing between adjacent holes, the roughness of the hole wall and hardness at the hole edge. Hardness was taken as HV10 across the heat-affected zone of the laser holes and at the edge of the drilled holes for comparison.
Results
| Measurement | Acceptance limit | Radial drill | 30 kW laser |
|---|---|---|---|
| Hole diameter | Class C tolerance | Pass | Pass · deviation similar to drilling |
| Adjacent hole spacing | ±1.0 mm | Pass | Pass |
| Hole wall | Ra ≤ 25 µm | Drill marks, burr at exit | Smoother; no burr |
| Edge hardness | HAZ ≤ 350 HV | Base metal | Higher than drilled; below 350 HV |
| Material removed | — | Full hole volume as chips | Kerf about 0.1 mm |
The result held for all four thicknesses, including 30 mm. On the thicker plates the laser needed slower settings for the holes than for the outer contour, which is normal and does not affect the outcome.
Reading the results
Diameter and roundness
A drilled hole takes its size from the drill, so as long as the drill is sharp the diameter is very consistent. A laser hole takes its size from the program and the kerf compensation. Once the compensation is set for a given thickness, the laser repeats just as well, and it can cut any diameter without a tool change. That is why the diameter deviation came out similar.
Position
On a radial drill, position depends on marking out or on a template, and on the operator. On the laser, every hole in a part comes from the same program and the same coordinate system, so spacing errors do not add up along a hole group. In practice, this is where shops see the biggest difference on site.
Hardness
Laser cutting heats a thin layer at the hole wall and that layer cools fast, so it is harder than the base metal. The question is whether it stays below the limit. In this test it did. Under EN 1090-2, the limit for grades up to S460 is 380 HV10, which is higher than the 350 HV we used, so the same holes would also pass that check.
Slip-critical joints. For friction-type high-strength bolted connections, the project specification may set extra requirements for faying surfaces and hole edges. Approval of laser-cut holes for those joints rests with the engineer of record. Raise it before fabrication, not after.
How to cut good bolt holes on a laser
- Pierce in the middle, not on the line. The pierce leaves a crater. Start in the centre of the hole and run in on a short arc so the pierce point falls in the scrap.
- Use hole settings, not contour settings. Small holes need lower speed and often pulsed output. Most controllers switch to a separate parameter set below a given diameter.
- Respect the hole-to-thickness ratio. As a working rule, holes close to or larger than the plate thickness come out round and square. Much smaller holes in thick plate are where quality drops.
- Measure both faces. A laser hole can be very slightly wider at the top than at the bottom. Check the smaller face against the tolerance.
- Cut holes before the outer contour. While the part is still held by the skeleton it cannot move, so holes stay where they were programmed.
On beams and channels, the same holes are cut in flanges and web from the DSTV file in one setup; see cutting from Tekla DSTV files and the H-beam laser cutting machine.
When to keep drilling
- The specification calls for drilled or reamed holes, or for Class A or B holes.
- Holes are much smaller than the plate is thick.
- Most of the work is holes with almost no profile cutting, and a drill line is already paid for.
For most fabricated steelwork with Class C holes, the laser does the holes in the same pass as the cut, and the drill line becomes a backup.
Questions
Are laser-cut bolt holes allowed in steel structures?
Yes, in most codes, subject to measured quality. AISC 360 has permitted thermally cut bolt holes since 2016 within roughness and gouge limits; EN 1090-2 permits thermal cutting where hardness limits are met; GB 50205-2020 accepts holes by measured diameter, position and roughness.
Does laser cutting make the hole edge too hard?
The edge is harder than a drilled one. In our test on Q355B from 12 to 30 mm it stayed below 350 HV, which is also under the 380 HV10 limit in EN 1090-2 for grades up to S460.
How small a bolt hole can a laser cut?
As a working rule, holes close to or larger than the plate thickness cut round and square. Smaller holes in thick plate are possible but need more care and should be checked on both faces.