I learned first hand the importance of using air assist with the laser cutter when I tried to cut out rubber gaskets. With no air flowing, the rubber cutting produced a flame about one inch tall. It was not an intense flame, but looked something like a burning candle. This flame did cover the CO2 focusing lens with soot after a few minutes of cutting.
I found that a 1 inch PVC pipe fit nicely over the lens mount in my SK40IV laser engraver. I machined a piece of 3/4 inch PVC pipe to slide inside of this outer pipe so that. Could attach an end cap with a hole in the center for air to flow out on to the work piece at the point of laser cutting. I added a small hose barb to attach 1/4 inch soft plastic tubing for that supply and routed the tube out the back of the laser cabinet. I am using a 12 Volt air solenoid to turn the air assist supply on and off. This supply attaches to the same power strip a the laser, the recirculating water pump, and the ventilation fans. By turning everything on at once, I can have some assurance of proper system operation.
With the air assist in place, cutting rubber only produced a small spark at the cutting point and no flame. The air is basically blowing out the flame continuously. I did not notice a significant difference in cutting performance for 1/4 inch plexiglas. I hoped that I could use a faster cutting speed with air assist, but at 40 Watts, I still needed to use the lowest speed.
I also added a “honeycomb” mesh to support the parts that I am cutting. With the entire part supported, I don’t need to worry about the cutting order. I previously ruined a part since the outside was cut before the inside. Since there is no mechanical force on the sheet being cut by the laser, supporting the whole part allows any order of cutting. I do not have Z axis adjustment, so I am restricted for now to cutting sheets of similar thickness. My lens focal length is not very short, so the optimum z position is somewhat forgiving. I can now very successfully cut fairly precise shapes out of 1/4 inch plexiglas.
I purchased the honeycomb mesh on eBay for a low price. The addition of air assist was also low cost since I built it out of lathe turned PVC parts and inexpensive air handling components: 1/4 inch air hose, hose barb, electrical valve, and a few pipe fittings.