I read from couple of places that these kind of nozzles are bad for the lens if they are designed improperly. They tend to work as vacuum cleaners -> pushing air out from nozzle and bring the smoky air into to the nozzle eg from the lens connection, making the lens dirtier faster. Mine is quite air tight since when i block the nozzle the pressure maintains quite well in the nozzle tube but leaks very little from somewhere so maybe i just need to design a new separate air-assist nozzle.
Silly question but could this be used as an airblower if tubing allowed for the air to be blown into a normal air assist type tube end.
It blows air (it also sucks but it has a blow option only)
I ask as I have one of these for dust extraction (used with the ash hoover in suck mode) but would it work as an air assist in ‘blow mode’.
… it will make a lot of noise but I’m sure it will work. But make sure it does not get too hot, they are not intended for hours of operation.
The same may apply for air compressors. as i bought the b+d compressor, the manual states that its intended for short time use. But i must at some point just try to go to the limits so that i know how long it can operate. And i maybe need some kind of fans to cool down the compressor heat sinks. This is an forever lasting enhancement process 
Jumping back a little bit to the original topic…
So i have now air-assist and seems like 100mm/min speed ~1.6mm/sec speed it takes 4 passes to cut through 4,5mm interrior hard plywood (birch) but the result is very carbonized. Edge is quite fine but still carbonized.
I started at focal length from surface and z-step 1mm down on each pass.
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These two images below shows result with external ply birch with 3 layers. The edge is not that fine and extremely burned in center of material
IMG_20200611_231404|666x500
Any suggestions what i could try to get less carbonized cut ?
Well my first tests showed that 600mm/min 20 passes and maybe i started from center of material thickness down i got a little better result:
Can the cut be any better (in last image) with this 6w laser, what do you think ?
I’m actually a little surprised, the last picture looks very reasonable for a diode laser. I only achieved similar results with my 5.5 Watt Chinese diode laser if I could get very special fine playwood and only with many laps. Finally, I got mad at all the soot and the many ruined items. But for engraving graphics, a good diode laser is great.
Actually my question was more that should i stick with the 600mm/min (10mm/s) speed or should it be possible to get similar results with 100mm/min (1.6mm/s) speed. The last image you refered to is cut 600mm/min 20 passes. But there is some factor that is still wrong with my current setup because one of the same run cuts as in the last image, i got better result event with 4 passes 100mm/min speed. Stil the slower speed got more soot but still better than my test yesterday.
Checking many of k40 video (much more powerfull laser), they run with slow speeds to achieve less sooty results.
Peter, one thing you need to be absolutely sure is that you have the same type of playwood for your trials or else you will be frustrated. Even on the same piece of wood, there are sometimes large differences between glue and number of knots in the many layers. I think if one’s machine is accurate enough, it must be preferable at many turns and high speed to avoid heating and blowing the ashes out of the track.
This is so true. Even when buying multiple sheets from the same source at once, you still can have quite some variance in between them.
yes, thats one mistake that i do 
and i noticed after several weeks of testing that the 4mm plywood i ordered was actually 4.4mm thick and that affects the focus when the focusing is made by adjusting the Z offset once i have calibrated the Z=0. I should make some kind of fixed measurement stick that would show mechanically the focal length.
But the speed of cutting is still confusing. I must do more tests with greater speeds (or something between 100-600 to find the optimal speed. The main thing that i see on the cuts are that the first cut is usually carbonfree / not sooty. Its this brownish very nice edge, but after this it starts to get sooty.
Thats maybe just the lack of pressure or positioning of the air-assist. Theoretically it would be a brown cut edge all the way thorugh if would run one pass, take a pause -> get the soot out to have a fresh wood surface at the bottom of the cut, and then cut another pass.
The k40 tests using air-assist seems to have the nozzle very near the material surace (like 5mm). My air-assist nozzle is seceral cm away. 2-3cm while the nozzle hole is 1.5mm.
I’m planning currently a new nozzle with separate air-assist tubing since i have read that the air inside the laser lens may make the lens dirtier faster. Still need to plan the tubing part. The nozzle is just to try to keep smoke out from intereferring the laser beam.
Final design is here
And the best result until this point is 600mm/min 20 passes with no z-stepping and 2 bars air from a ~1.5mm nozzle
The once seen below are cut with 20 passes (2 with z-stepping and 2 with no z-stepping)
2 of the hexagons are started with z in middle of material and 2 from surface. All seems quite same result so i think the best is to use no z-stepping with currents setup.
And here you can see the final 3d printed nozzle air-assist thinker
remarkable result for a diode and 4mm playwood you should have patent on this nozzle, congratulations
once thing i still have to do is make a flexible pipe from the laser cooler fan outside the enclosure so that “fresh” air is fed to the laser cooling and not recycled smoke fume air.
It should be possible to make a branch from your nozzle supply. It is limited how many liters of air you get through a specific pipe diameter at a specific pressure. There should be plenty of air for this too.
The compressor i have is not for continuous use, so i think i will take the air from the roof of ther enclosure. because the air outside is quite clean.
But now when you said this, it could be possible whit a larger compressor to remove the laser fan and feed the compressed air from there, through the heat sink into the nozzle and make the nozzle have a hole of some somewere between 1-3mm. It could totally prevent smoke from getting in contact with the lense and the clean air would be blown from straigt above the cut. 
Your nozzle looks fine but I have always run with air through the laser hole itself, without any problems at all. I know that a vacuum effect can occur but think that the airflow itself prevents polluted air from sticking to optics. What do you have as an extractor? If your suction is strong enough, it sucks the dirt out anyway.
just an ordinary wall extractor.
100mm diameter with specs stating 100 m3/h
The Enclosure is aprox 0.7m3 so according to that it should be empty of smoke in maybe 30 seconds in theory.
About the first version where the air came from same nozzle as laser, i was thinking the the smoke could be sucked through the laser optics -> which was why i changed the design since i dont know how tight the optic lense is.
How often do you clean your lens -> just the visible lense of your laser ?
When I work with my diode laser, I might clean every two weeks, they have rarely been dirty. With my K40 CO2 laser, which also only runs with a small 24V radial fan, I clean it simultaneously with the # 2 mirror. No. 2 mirror is most exposed because it “hangs freely in the box” without protective airflow. However, the mirror and lens in the nozzle head are not very often dirty. But lately I’ve been working a lot with MDF, it gives bad smoke that sticks to the machine bed, now I check my optics every other week and it’s still not so much dirty, thanks to the airflow.
By the way, it is an advantage if there are a number of holes in the front of the laser bed housing itself for suction, best below the bed height and preferably adjustable. If you hold a small piece of paper in front of the holes, the paper should be sucked but not too strong, a moderate vacuum is perfect for the optimal airflow inside.
ok thats a good tip.
I started to google the k40. Maybe some day i will upgrade but im curous what is the liftime of the co2 ?
And where did you buy your k40 from ?
If its possible to start private discussion, it would be good. I didnt find a place to send privet messages…