TCP in H-Beam Laser Cutting: How the Head Stays on the Line
PCL Group application engineering, Jinan · Updated 20 October 2026
Tilt a laser head and the focus point moves. It is simple geometry, and it is the reason a 5-axis machine needs TCP control. On an H-beam, where the head tilts for every flange face, root radius and bevel, TCP decides whether parts fit.
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The tool center point
The tool center point (TCP) is the point that does the work. On a laser head it is the focus of the beam just below the nozzle. When the head only moves up, down and sideways, the TCP simply follows the axes. As soon as the head rotates, it does not, because the head turns around a pivot that sits some distance above the nozzle.
A worked example
Take a head whose pivot sits 110 mm above the focus point (the figure is only for illustration; every head is different). Tilt it 35° for a bevel without any compensation:
- Sideways shift
- 110 × sin 35° ≈ 63 mm
- Height change
- 110 × (1 − cos 35°) ≈ 20 mm
The beam would land 63 mm from the line and 20 mm out of focus. TCP control removes that error by moving the linear axes at the same time as the rotary axes, so the focus stays on the programmed point at every instant of the move. The controller does this continuously along the move, not just at the end points.
Controller makers use different names for the same function: TCP or TCPC, RTCP (rotation around tool centre point), TRAORI on Siemens controls, TCPM on Heidenhain.
Where it matters on an H-beam
| Feature | What the head does | What TCP protects |
|---|---|---|
| Holes in the web | Head vertical | Nothing to compensate; a reference case |
| Holes in flanges | Head turns to face each flange | Hole position on the flange |
| Copes through the root radius | Head rotates continuously round the radius | A smooth cut with no step at the radius |
| Weld bevels | Head tilts up to ±45° | Bevel angle and root face along the edge |
| Cut-to-length with bevelled ends | Tilts while crossing flange, radius and web | A square, continuous end cut |
The PCL H-beam laser uses three linear axes (X, Y, Z) and two rotary axes on the head: A rotating through 360° and C tilting through 180°, with bevels to ±45°. The axis layout is drawn in 5-axis 3D laser cutting; the bevel types are in beam bevel cutting.
Video: watch the head tilt through the cope, the radiused access hole and the bevel while the cut stays on the line.
TCP and the real beam
TCP keeps the head on the program. It does not know where the beam actually is. Rolled sections come with flange tilt, web offset, camber and twist inside their mill tolerance, and on a 12 m beam those add up. That is why the machine measures the section before cutting and shifts the program to the beam on the bed. TCP and section measurement work as a pair; either one alone leaves errors in the part.
Keeping TCP accurate
- TCP depends on the controller knowing the exact distance from pivot to focus. If that number is wrong, every tilted cut drifts.
- Re-run the TCP calibration after a head collision, after changing the nozzle body or focus settings, and at the interval in the machine manual.
- A quick check: cut a short bevel on a test piece at +45° and −45° and measure that both land on the same line.
- On bevels, the cut runs through more material than the nominal thickness (about 1.4 times at 45°), so use bevel parameters, not straight-cut ones.
Questions
What does TCP mean in laser cutting?
TCP is the tool center point, the focus of the laser beam below the nozzle. TCP control keeps that point on the programmed path while the head tilts and rotates.
Is RTCP the same as TCP?
In practice yes. RTCP (rotation around tool center point), TCPC, TRAORI and TCPM are names different controllers use for the same compensation.
Does TCP correct for a bent or twisted beam?
No. TCP keeps the head on the program; section measurement before cutting adjusts the program to the real beam. Both are needed.