Generic 20mm Beam Combiner Lens

Here is how a combiner works. It is a flat optical window with a special coating, set at 45 degrees in the beam path. The CO2 beam at 10,600nm passes straight through it. A red diode laser shines at the combiner from the side, and the coating reflects that red beam so it travels on exactly the same line as the CO2 beam.

• The CO2 beam goes through the combiner, then on to mirror one as normal.
• The red dot joins it at the combiner and follows the same mirrors to the head.
• The focus lens passes visible red too, so the dot lands on the work where the laser will fire.

The result is a red dot on your material that marks the cutting point, with the tube switched off. That is the feature many owners envy on larger machines, and the K40 never had it from the factory.

Beam combiners are usually made of zinc selenide, which transmits both CO2 and visible red light. This part does not state its material, so treat it with the same care as any ZnSe optic until you know otherwise.

The 20mm option shown is 2mm thick; a 25mm size is offered too. Pick the diameter that matches the combiner holder you plan to use, since the combiner sits in its own mount rather than in a mirror or lens seat.

If you came looking for a focus lens, stop here and see the Cloudray 20mm focus lens instead.

1. Pull the plug and give the laser supply time to bleed down; the high-voltage lead runs through the tube bay where this part goes.
2. Measure the gap between the tube's output end and mirror one. The combiner holder must fit there without blocking the beam.
3. Fit the holder so the combiner sits at 45 degrees to the beam, with the red diode mounted to hit it from the side.
4. Seat the combiner by its edge, wearing gloves, with the coated face oriented as the holder maker specifies.
5. Power the diode from a separate low-voltage supply, never from the tube circuit.
6. Align the red dot to the CO2 beam at mirror one, then check it at the far corners.

The last step is the real work. The red and CO2 beams must leave the combiner on the same line. If they diverge even slightly, the dot drifts away from the true cutting point as the head moves further from the tube.

Once aligned, leave the combiner alone. Knocking the holder puts the dot out of step with the laser, and a pointer you cannot trust is worse than none. The K40 upgrade guide covers the other jobs worth doing while the tube bay is open.

It does not replace mirror alignment. The red dot follows the mirrors, so if a mirror is misaligned, the dot goes wherever the beam goes. It shows where the beam lands, not whether the path is centred on each mirror. Use tape targets for alignment, as the alignment guide describes, and use the dot for positioning.

• Good for: positioning work, framing a design, checking the head's start point.
• Helpful for: spotting gross misalignment quickly, when the dot falls off a mirror.
• Not for: fine alignment, focus setting, or judging beam quality.

Every optic in the path costs a little. A clean, well-coated combiner loses a small share of the CO2 beam and adds one more surface to keep clean. Smoke rarely reaches the tube end, so it fouls far more slowly than the head optics.

Clean it rarely and gently: puff away dust, and only if a film remains, make one pass of isopropyl on lens tissue. If the coating shows spots or haze, replace it.

A dim dot on bright material is common. Dim the room or use a stronger diode module if the dot is hard to see.

The combiner is the more accurate route, because the dot sits on the beam at any height. A side-mounted pointer crosses the beam at an angle, so it is right at one height and wrong at every other.

A combiner also keeps working when you change lenses or bed height, which suits owners who switch between focal lengths.

Get the calipers out and check:

• The diameter your combiner holder takes, 20mm or 25mm.
• Room between the tube's output and mirror one.
• A red diode module and power supply for it.
• Your patience for one careful alignment session.

If your beam path needs attention first, do that job before anything else.

Still learning? The K40 how-to shows how to position work without a red dot, using low-power test marks on masking tape.