Nozzle beam trace — how a small beam error becomes a double line
A double line that comes and goes across the bed is often the beam brushing the inside of the nozzle on its way out. Step through the guided sequence, press Play to run it as a slideshow, or drag the sliders to set your own misalignment and watch where the beam lands.
What this can't tell you. This is a teaching model, not a measurement of your machine. It traces one plane of a simplified head with an assumed tube bore and nozzle cone shape, so the exact angle where clipping starts on your machine will differ — the trends hold. It shows beam-path causes only; a double line can also come from a loose belt or pulley, a dirty or cracked lens, or a lens seated upside down. Confirm with a tape test at the near and far corners before you adjust mirrors.
- Spot walk on mirror 3
- Beam tilt down the tube
- Off center at the lens
- Off center at the nozzle tip
- Focus shift on the work
- Lean of the exiting beam
Angle is the error that reaches the nozzle
A beam that is parallel but off center still gets steered to the focal point by the lens. A beam that is tilted moves the focal point itself, by focal length × tilt.
A longer lens doubles the lever arm
A 4.0″ lens sits about twice as far from the nozzle tip as a 2.0″ lens. The same tilt drifts twice as far sideways before it reaches the orifice.
The bounce makes the second line
When one edge of the converging cone grazes the inside of the nozzle it reflects and leaves the orifice on a different path. That is the ghost line beside the main one.
A wider nozzle hides the error
With the 6 mm nozzle the same error exits clean. The beam is still tilted, so the focus is still shifted and the cut still leans.
Model: 2D geometric ray trace of one plane, from mirror 2 to the material. Lens set follows Thunder Laser's Nova and Titan options (1.5″, 2.0″, 2.5″ and 4.0″ nominal focal lengths; 2.0″ is standard on Nova, 2.5″ on Titan). Nozzle openings are the two Nova nozzles, 2 mm and 6 mm. Nozzle-to-work gap follows the Nova reference focus gaps: about 3.5 mm for 1.5″, 6 mm for 2.0″ and 10 mm for 4.0″, with 2.5″ assumed at 6 mm. Titan lens tubes all hold about 5 mm. Raw beam is 5 mm, the listed figure for 60 to 100 W Nova tubes. Assumed, not from published specs: 18 mm tube bore, nozzle cone shape, and head height. The nozzle wall is treated as a mirror at 10.6 µm and the tube wall as absorbing. Exact thresholds change with real dimensions; the trends do not.
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