Laser Cutting Edge Quality - Steel

In this article, we describe edge quality and cut tolerances for steel laser-cut parts from 1/8" to 3/4" thick A36 steel (generic low-carbon "mild steel.")

In general, the edge quality on laser-cut steel parts depends on laser power, assist gas, and laser type (i.e. CO2 or fiber).  Our laser is a 3 kW Trumpf Trudisk laser (basically, a fiber laser).  The results we show here will give you a good idea what you can expect to see from our laser-cutting machine, but may not represent what all fiber lasers will do, or how all fiber lasers compare to older CO2 lasers. 

steel finish quality top angle.jpg

Edge quality on laser-cut steel parts from 1/8" thick to 3/4".  These parts were cut on a 3 kW Trumpf TruDisk laser.  No post-operations (sanding or deburring) were applied.

Note that all of these parts were laser-cut using oxygen assist gas.  Nitrogen produces a better surface finish and faster cutting speeds on steel up to 1/4" thick.  Thicknesses greater than 1/4" thick require oxygen.  You can learn more about the differences between oxygen and nitrogen cuts on our laser cutting with oxygen vs. nitrogen article.

Part Tolerances

The machine itself has a rated position tolerance of 0.005" over the entire 5' x 10' bed.  Neglecting other factors that may affect accuracy (like kerf) the end-to-end length of a part can be expected to fall somewhere within that range.  Smaller parts tend to be much better, as will be shown.  The laser-cutting head may be off by as much as 0.005" over ten feet, but over a handful of inches, it does a much better job. 

All of the test parts shown in this article were 2" x 5".  Only the cutting tolerance measurements for the 2" dimension are shown, but at 5" the performance was identical.

Because the beam tends to expand as it passes through the metal, you can expect the part width to be smaller on the bottom of the part, compared to the top.  The effect is usually minimal, within one or two thousandths of an inch.  At 3/4" thick steel, the effect becomes much larger, as discussed below.

Table 1 (below) summarizes the part width error on the top and the bottom of the material after a cut.  More details about each material thickness - including images of the edge quality and measurements - are provided below.

Table 1 - Part width tolerances for a 2" x 5" laser-cut part in steel thicknesses ranging from 1/8" to 3/4".  Data shows width tolerance at the top of the part, and separately on the bottom of the part to characterize the impact of changing beam width through the part thickness.

Laser Cutting Edge Quality on 1/8" Thick Steel

Our fiber laser really shines when cutting eighth-inch mild steel.  Cutting speeds are high, and usually the edge is pristine.  The reflective, glassy edge shown below is the product of an oxygen cut.  Some people prefer that finish, but it is less suitable for painting and other finishing operations - the shiny scale has to be removed before paint will adhere.

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Laser cutting edge quality on 1/8" thick steel, using oxygen assist.  No post-operations applied.  there is a small burr on the edge on the right-hand side that could be avoided by tweaking laser-cutting parameters (cut speed, focus distance, gas pressure, etc.)

Laser Cutting Tolerance on 1/8" Thick Steel

Part widths for the 1/8" thick steel parts are shown below.  The image on the left shows the part dimension on the top of the cut.  As shown, it is within 0.001" of the target part width.  In the right image, we moved the calipers so that they only made contact with the bottom of the part.  As shown, the part is between one and two thousandths smaller at the bottom of the part.

Eighth inch edge dimension.jpg

Part width on 1/8" thick laser-cut steel.  Designed part width was 2.0".  Actual part width is within 0.001" of the target.  Measurement was taken at the top of the part.

Eighth inch bottom edge dimension.jpg

Part width on 1/8" thick laser-cut steel, measured at the bottom of the cut.  Beam expansion decreases the width of the part by less than 0.002".

Laser Cutting Edge Quality on 1/4" Thick Steel

Quarter inch laser-cut steel edge qualit

Laser cutting edge quality on 1/4" thick steel, using oxygen assist.  No post-operations applied.

Laser Cutting Tolerance on 1/4" Thick Steel

Quarter inch laser-cut steel top edge di

Part width on 1/4" thick laser-cut steel.  Designed part width was 2.0".  Actual part width is within 0.001" of the target.  Measurement was taken at the top of the part.

Quarter inch laser-cut steel bottom edge

Part width on 1/4" thick laser-cut steel, measured at the bottom of the cut.  Beam expansion decreases the width of the part by 0.001".

Laser Cutting Edge Quality on 1/2" Thick Steel

Half inch laser-cut steel edge quality.j

Laser cutting edge quality on 1/2" thick steel, using oxygen assist.  No post-operations applied.

Half inch laser-cut steel top edge dimen

Part width on 1/2" thick laser-cut steel.  Designed part width was 2.0".  Actual part width is within 0.001" of the target.  Measurement was taken at the top of the part.

Half inch laser-cut steel bottom edge di

Part width on 1/4" thick laser-cut steel, measured at the bottom of the cut.  Beam expansion decreases the width of the part by 0.005".

Laser Cutting Edge Quality on 5/8" Thick Steel

Five eighths inch laser-cut steel edge q

Laser cutting edge quality on 5/8" thick steel, using oxygen assist.  No post-operations applied.

Five Eighths inch laser-cut steel top ed

Part width on 5/8" thick laser-cut steel.  Designed part width was 2.0".  Actual part width is within 0.001" of the target.  Measurement was taken at the top of the part.

Five eighths inch laser-cut steel bottom

Part width on 5/8" thick laser-cut steel, measured at the bottom of the cut.  Beam expansion decreases the width of the part by 0.006".

Laser Cutting Edge Quality on 3/4" Thick Steel

Three quarter inch laser-cut steel edge

Laser cutting edge quality on 3/4" thick steel, using oxygen assist.  No post-operations applied.

Three quarter inch laser-cut steel top e

Part width on 3/4" thick laser-cut steel.  Designed part width was 2.0".  Actual part width is within 0.005" of the target.  Measurement was taken at the top of the part.

Three quarter inch laser cut steel botto

Part width on 3/4" thick laser-cut steel, measured at the bottom of the cut.  Beam expansion decreases the width of the part by 0.036".