Russ Sadler points out that Chinese CO2 lasers lack air inlets matching their 6 inch = 150 mm outlet port, so fumes accumulate over the workpiece as air leaks in through various panel / hatch gaps and small openings. The simplest solution, at least for my OMTech 60 W laser, seems to be opening the front passthrough hatch:
The opening is 33×4 inch = 0.9 ft² with an airflow of just under 1 m/s into the exhaust fan at full throttle, so it’s venting at about 180 CFM. That’s half the duct fan’s 400 CFM in more-or-less free air, but the laser cabinet outlet vent has a perforated cover with maybe 50% clear opening:
It’s not exactly a flame arrester.
Directing the air flow across the platform from front to rear requires sealing the gaps along the front of the cabinet:
And the huge openings on either side of the exhaust duct:
Yes, all those are cardboard sheets and, no, they’re not the final implementation. This is all in the nature of figuring out what works, so being able to cut-to-fit is a Good Idea.
The large gap along the rear edge (on the right, above) for the rear feedthrough opening got a cardboard sheet after engraving some MDF.
Early indications are that it works fine, as witness the smoke streaming off the rear of a cardboard test piece:
Cutting MDF produces copious smoke that fills the cabinet, but it clears quickly and doesn’t escape into the Basement Laboratory if I wait a little longer than I really want to after the cutting stops.
Blocking the unused areas of the honeycomb helps direct airflow in the proper direction:
All in all, it works well.
The Smell of Molten Projects in the Morning 
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