What we provide here is meant to be rules of thumb. There are a lot of factors that impact the absolute maximum thickness a laser can cut, ranging from material purity to head design to operator skill.
At 60kW, lasers can cut carbon steel up to 1.75″ using nitrogen assist gas and up to 3″ using oxygen with a highly skilled operator. For those using general labor or inexperienced operators to operate the laser (common in the US), those thicknesses back down to 1.5″ and 2.75″ respectively.
The table below represents the maximum capabilities of each laser power on mild steel at the hands of a skilled operator and under normal operating conditions.
At Fairmont, we talk about “throw-and-go” production. This considers an average operator and lot-to-lot variability common to raw material. If you are hoping to throw a piece of material on your machine and cut based on saved parameters, we recommend backing down each of these thicknesses by .25″.
| Laser Power | Mixed Gas Cutting - Skilled Operator | Oxygen Cutting - Skilled Operator |
|---|---|---|
| 60 kW | 1.75" | 3.00" |
| 40 kW | 1.50" | 2.75" |
| 30 kW | 1.125" | 2.50" |
| 20 kW | 0.875" | 2.25" |
| 15 kW | 0.50" | 2.00" |
| 10 kW | 0.375" | 1.50" |
| 6 kW | 0.25" | 1.25" |
Nitrogen-Based Cutting
When using nitrogen-based assist gas, an underpowered laser will produce enough burr to tack weld the part to the slats. This can quickly become a nightmare situation, as the only way to separate the parts from the slats is by crowbar – often with several scrapped slats.
Oxygen Cutting
If possible, you want to cut with nitrogen or mixed gas, but if the burr becomes too great then you switch to oxygen assist gas. But even oxygen can’t cut infinitely thick – as it is eventually limited by heat. While cutting with nitrogen-based assist gas is fast enough to prevent meaningful heat build-up, thick cutting with oxygen can drop to very slow speeds. And at slow speeds, heat begins to build-up very quickly.
Fairmont experience shows us that when the cutting head traverse speed drops below 100 ipm heat can be an issue, and when it drops to 25 ipm it is always an issue. Heat buildup can warp the material but more importantly, it affects the cutting head. Excessive heat impacts beam alignment and throws off the magnetic field that controls standoff height. Both negatively impact cut quality – which generates more heat and starts a vicious cycle.
Heat is more of an issue on intricate parts where the cutting head is going to be cutting in a relatively small area for a while, as opposed to long straight lines or arcs where the head is moving to new cooler areas of the plate. Here are some things to consider about heat:
Metals expand when they are heated. We have seen the cutting of a tight nest where the material by the end has moved enough that the path of one part crosses over into another. Also, material can warp under heat. However, the most common warpage problem we see doesn’t actually have to do with heating the material, it has to do with relieving the stresses already present in the sheared or flamed edge of the raw sheet. To avoid this kind of warpage stay clear of the stressed edge by ½”.
To see the true impact of heat you need to see what happens as a full plate is cut. You can learn a little from cutting one part, but most issues come from prolonged cutting on a plate as you work your way through a nest.
When programming a nest, bounce from one end of the machine to the other. Cut a bit, bounce, cut a bit, bounce. A similar and even more effective approach involves giving the material time to cool. Some programmers cut part of a plate using the bouncing technique, then go to another plate and cut the same pattern, then return to the first plate to finish the nest, etc. This approach gives time for the plate to cool. Programming nests in this way is far more complex than bouncing from area to area on one sheet or plate, but it is the most effective for mitigating heat issues.
If at all possible, avoid cutting with oxygen. Oxygen cuts with much higher heat than nitrogen-based assist gas, and it cuts slower – a double-edged sword. If you have enough power to avoid tack-welding the parts and skeleton to the slats, then cut with nitrogen or mixed gas.
At Fairmont, we separate laser capabilities into two groups. “Throw-and-go” production and “Skilled” production. You can read about what makes a good laser operator in the Fairmont article published in the Fabricator (here).
“Throw-and-go” production is for the everyday operator. At a given power level, any attentive operator that has basic training can throw a sheet of A36 into the cutting envelope and cut it with good to excellent results.
“Skilled” production stretches the capability of the machine to its limits. Cutting these advanced applications requires expertise. Fairmont offers advanced app training classes to help move operators to the next level. Skilled operators can exceed each of the throw-and-go thresholds by approximately .25″. For example, a skilled operator with a 40kW laser can cut 3.00″ with oxygen assist gas. But to do so, that operator would need to keep the laser operating at optimal conditions and dial in cut quality every time the batch of material changes, as even small changes in material composition can dramatically affect results when you are at the edge of machine capability.
Those that experience high turnover or employ general labor to operate their laser(s) should not consider themselves as “skilled” and should not push beyond throw-and-go machine limits. There is no issue with employing general labor to operate the machine; at Fairmont we have countless customers that operate this way with tremendous success. But it is important to honestly self-assess and understand which group your shop falls into.
Author: Alex Burnham, Senior Product Manager, Fairmont Machinery
Technical Review: Chip Burnham, Owner & CEO, Fairmont Machinery
Last updated: October 2026
