English 
Here are some real world considerations to take into account:
1 .When cutting any organics, you need to run at the safe maximum operating current for your tube.
Then you carry out some cutting trials starting at high speeds, gradually decreasing the speed until you are consistently cutting through the material.
2 .Air assist is needed to protect the lens and to blow smoke out of the kerf (the thickness of the laser cut). This is because the smoke will disperse the laser beam. You do not need excessive air pressure, an aquarium pump is more than sufficient.
The air assist becomes more effective the closer the nozzle is to the surface of the material.
The closer the air assist to the material, the higher the chance of contaminating the surface of the material with smoke debris.
When air assist is too low, it is possible for the laser beam to ignite the smoke.
This video on Relief engraving and Air Assist gives a good overview of how air assist works in laser cutting and engraving.
Pro Tip: For acrylic, a high air assist can decrease cutting performance as it cools the cut down.
3. Good effective extraction is needed, you need to be able to see the smoke being pulled away from the work piece.
Set your laser to it’s maximum safe operating power with air assist on high. Use a 2″ lens for MDF thicknesses up to about 6mm and a 2.5″ lens for thicker than 6mm. Cut some test 25mm squares, starting at a high speed and gradually decrease the speed. When you are cutting through the MDF consistently, take a speed 2~3mm slower to take into account variations in the material. Ensure you have good extraction and a decent airflow across the top and bottom work surfaces. A good cut should give very little soot on the cut surface.
MDF is an engineering wood product held together by adhesives. It has the same issue as plywood with the potential to form formaldehyde gas. However, there are now some “laser friendly” low formaldehyde mix MDF sheets on the market. Engraving is easier on MDF as it has a more consistent surface, although the results can be quite bland. You can also get MDF veneers that offer the benefit of a consistent cutting performance, with the beauty of a finished surface
