How to Cut an H-Beam with a CNC Plasma Cutter: Step by Step
To cut an H-beam on a CNC plasma cutter, support the beam, measure the real section, cut holes and inner features first, then copes, marks and finally the end cut. Most quality problems come from skipping the measurement, wrong speed for the thickness or worn consumables.
At a glance
- Measure the section before cutting; rolled beams are never perfectly straight.
- Cut holes and access holes first, the end cut last.
- Keep plasma holes at least about 1.5× the flange thickness.
- Dross and bevel usually mean wrong speed or worn consumables.
On this page
Step by step
- Load and support the beam. Place the H-beam web vertical on the bed supports, with enough overhang at the cutting zone that the torch can reach both flange edges.
- Measure the section. Rolled beams are never perfectly straight or square. The machine probes or scans the flanges and web and corrects the program to the real beam.
- Cut inner features first. Bolt holes, slots and weld access holes are cut while the beam is still full length and rigid, so they stay in position.
- Cut copes and notches. Flange and web cuts for connections follow, with the torch tilting where a bevel is needed.
- Mark the part. Part number and fit-up lines are marked before the part is cut free.
- Cut to length last. The end cut releases the part; the next part starts from the new end.
Parts come from DSTV files exported by the detailing software; see cutting from Tekla DSTV files.
Common problems and how to fix them
| Problem | Usual cause | Fix |
|---|---|---|
| Holes oval or out of position | Beam not measured, or flange not square | Probe the section before cutting; check supports |
| Heavy dross on the bottom edge | Speed too high or too low for the thickness, worn consumables | Adjust speed to the thickness chart; replace nozzle and electrode |
| Excessive bevel on square cuts | Worn nozzle or wrong torch height | Replace consumables; check height control |
| Small holes not round | Hole too small for plasma at that thickness | Keep holes at least about 1.5× the thickness, or use laser |
| Part shorter or longer than drawn | Kerf not compensated, beam moved during cutting | Set kerf compensation; clamp or support the beam firmly |
| Copes do not fit the column | Beam rotated or flange tilted | Measure flange tilt and correct the program |
Checks before the part leaves the machine
- Length and end square to the drawing tolerance.
- Hole size and position on both flanges and the web.
- Cope radius free of notches, especially at weld access holes; see weld access holes and beam coping.
- Bevel angle and root face where welds are specified; see beam bevel cutting.
- Dross removed from edges that will be welded or painted.
When to move from plasma to laser
If grinding, hole rework or tail-end scrap take more time than the cutting itself, a laser usually pays back: it cuts small holes and slots round, holds bevel angles, and with no chuck leaves no tail on the bar. See the H-beam laser cutting machine and zero-remnant beam cutting.
Questions
How do you cut an H-beam with a CNC plasma cutter?
Load and support the beam, let the machine measure the section, cut holes and inner features first, then copes and notches, mark the part and make the end cut last.
Why cut holes before the end cut?
While the beam is full length it is rigid and stays where it was measured, so holes and slots end up in the right position.
Why are plasma-cut holes in thick flanges not round?
Small holes relative to the thickness are hard for plasma. Keep holes at least about 1.5 times the flange thickness, or cut them with a laser.
What causes dross on plasma-cut beams?
Usually a cutting speed that does not match the thickness, or worn nozzles and electrodes. Adjusting speed and replacing consumables solves most cases.
Can plasma cut weld bevels on H-beams?
Yes, with a bevel torch. Expect light grinding before welding; a 5-axis laser gives bevels that are usually ready to weld.
Send an H-beam drawing for a test cut
Machine specifications and power options: H-beam laser cutting machine. Section dimensions: steel beam size chart.