A carbon fibre sheet is not carbon: it is a fibre + resin composite. A laser does not cut the fibres cleanly and burns the resin, with serious consequences for you and the machine.
What actually happens
The epoxy resin binding the fibres burns long before the fibres give way: the cut fills with charred resin, frays, and the part loses its mechanical strength — a problem when strength is precisely why you chose the material.
The fumes contain epoxy degradation products, irritant and respiratory sensitisers, along with fibre dust.
That carbon dust is conductive: it settles inside the machine and can short-circuit electronics and control boards.
What to use instead
To cut a composite sheet, the only clean route is mechanical: a CNC router with a diamond tool and extraction, or a diamond saw. The result is crisp and the fibre stays structural.
For a shape prototype, cut the part in plywood or acrylic with the laser, validate the geometry, then have the final part made in composite.
Fibreglass and epoxy sheets (including FR4 printed circuit boards) raise exactly the same problem and must also be excluded.
Every figure on LaserSettings comes with the machine, the laser source, the material and the thickness it was tested on. A setting published for a 10 W diode says nothing about a 40 W CO2, and a setting for 3 mm says nothing about 6 mm: check those four things before you copy any number.
Settings are confirmed or disputed by the members who reproduce them, so reliability comes from cross-checking rather than popularity. Photos of the result — cut edges, engraving shades, scorching — tell you more than a single number found on a forum.
Whatever the material, treat a published setting as a starting point: run a small power/speed test grid on an offcut, clean the lens, redo the focus, work with fume extraction and air assist, wear glasses rated for your wavelength and never leave the machine unattended.