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Setup & CalibrationModule 3.1~3 min read

Focusing: Three Methods

Focus is the single biggest variable in fiber laser quality. A few tenths of a mm off and a mark goes from crisp black to muddy gray.

MATERIAL TOO CLOSElensfocal pointspot: wide and softThe beam lands before it hasnarrowed: weak, blurry marks.IN FOCUSlensfocal pointspot: as small as it getsAll the power in the smallestspot: crisp lines, deepest cut.MATERIAL TOO FARlensfocal pointspot: wide and softThe beam has already spreadback out: the same soft result.
The cone of light is the same in all three. Only the height of the material changes, and with it the size of the spot that does the work.

1. Focus stick (the universal method)

OMTech ships a metal focus gauge, a stick the exact length of the lens's focal distance from the bottom of the housing. Lower the head until the stick just contacts the part, then raise the head by the stick's diameter offset (or however your stick is calibrated). Done.

  • 70mm lens: focal distance from the lens face is ~78mm (the working distance differs from the focal length number).
  • 150mm lens: focal distance from the lens face is ~187mm.

2. Red-dot crossing

Some OMTechs have two red dots that converge at the focus point. Move Z until they overlap into a single dot. Fast and reasonably accurate; verify against focus stick once a month.

3. Ramp test (highest precision)

  1. Tilt a piece of stainless or anodized AL on a wedge, known angle (e.g. 5°).
  2. Engrave a thin horizontal line at "nominal" Z.
  3. The thinnest, sharpest part of the line is true focus. Measure where on the ramp it appears, calculate Z offset, adjust.
THE SETUPhead travels, height fixedfocuswidesharpwideEngrave one line up a shallow wedge.The head stays level, so the surfacepasses through focus partway along.THE RESULTthin edgethick edgethinnest and sharpest here:this height is true focusMeasure along the wedge to thesharpest point, then set your focusto the height at that spot.
The slope is exaggerated here; a real wedge rises only 5 to 10 degrees. Because the head never changes height, the line itself shows you where focus is.

4. Find focus by ear, then cut a focal stick per lens

The classroom method for dialing focus on a lens you've never characterized, and turning the result into a permanent tool:

  1. Put a stainless plate on the bed with a dark anodized business card on top (the mark is easier to see on the card).
  2. Draw a small circle and fire it on run-continuously at moderate settings (60% power / 70 kHz is the classic test on a 60W MOPA-class source; scale to taste).
  3. Move Z up and down while it burns. True focus is where the burn is loudest and brightest. The snap is unmistakable once you've heard it.
  4. At that Z, caliper the distance from the bottom of the galvo cube to the top of the part.
  5. Cut a focal stick to that exact length, label it with the lens, and keep one per lens. From then on, focusing is "stick touches part, done", no chart, no math.

Test marks without losing focus: business card on the part

When you need to verify settings before committing to an expensive part, don't move the part and don't refocus. Lay a business card on top of the part and test-mark the card. The card is thin enough that focus height is effectively unchanged, and the part underneath never gets touched. Card confirms the mark, card comes off, job runs.

Watch for
For deep engraving you'll want to refocus between passes, as material is removed, the part surface drops away from focus. Lightburn supports Z-step per pass for this. Typical: drop Z by 0.05-0.15mm per pass on steel.