There is little screw lever that controls the air flow to the nozzle. I never paid attention to it before. It seems to have normally been in the position where no air is allowed to blow through: I think the air goes to the nozzle to cool it, but does not come out of the other side. If I change the lever to the opposite maximum, I can blow the air, and it goes through the laser beam hole, which it shouldn’t do, right? What’s the science benind this?
When the air is flowing properly, is usually goes out the hole at the bottom of the lens tube on the laser head. The air keeps the burnt materials from getting on the bottom of the lens, and also helps blow out any flames that might arise on what is being lasered. Some lasers have the air tube outside the lens tube, with it down near the surface to be lasered, so it can blow off the heated materials from the side.
Can you give us a link to this device to control your airflow looks like?
How does it cool the nozzle if it doesn’t come out anywhere?
Um… Makes sense. If it goes in, it needs to come out 
. It’s very basic, smth like this: https://5.imimg.com/data5/NT/XS/ZD/SELLER-11067367/co2-laser-head-mount-for-lens-and-mirror-for-engraving-cutting-machine-1000x1000.jpg
So it needs to be fully open then…
The air should blow out of the opening at the bottom of the cone nozzle. It is not to cool the nozzle, as there should be no heat generated within the lens/nozzle. Rather the air is to keep the lens clean and to blow smoke out of the path of the laser.
But air helps fire burn?? Because i was cutting plywood and saw small flames turned the air assist up and the flame got a bit bigger and was more red hot wood.
That is correct, oxygen is needed for a fire, but in the right mixture with (wood) gas. As @Fred perfectly describes it, air support on a laser is intended to blow dirt and fire out with a strong enough air flow. The effect can be seen even better when cutting acrylic.
Hi.
Yes, but only up to a point.
^This.
The issue with air when it comes down to assist in burning is that it contains ~78% nitrogen and only ~21% oxygen.
The airflow also cools down the material that’s cut and creates turbulence that thins the woodgas even further, so there’s a certain point when the oxygen in air doesn’t assist in the burning process anymore.
And that’s actually a very good and in most cases a desirable thing.
Because ample airflow helps to reduce charring and generally makes the cut smoother on materials that burn or melt easily.
The term “Air Assist” is somewhat misleading in this application since the air usually doesn’t assist in the burning process.
“Air Support” @bernd.dk mentioned would be more accurate.
Because oxygen and certain oxygenating gasses are easily available to the general public, IMO a word of caution is necessary.
While oxygen is used as a cutting gas (much like in the oxy-acetylene cutting) in certain industrial scale laser cutting methods,
oxygen or oxygenating gasses should never, ever, be used with a hobby laser
in the hopes of increasing the cutting capacity or -ability.
Doing so is just a disaster waiting to happen.
Regards,
Sam
I’ve been blowing matches out for decades… Didn’t seem to help them burn 
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…and then there are those who think it is a brilliant idea to grease the threads of the protective cap or pressure regulator of oxygen bottles… 
No seriously, I don’t think any mixed gas or shielding gas is used in our segment of laser business. Cutting any metal is a completely different story… Nitrogen, oxygen and helium are used here and sometimes other noble gases, depending on the material to be cut. And of course there is still dried high-pressure air.
Hi.
Exactly.
The same folks tend to clean their greasy overalls with pure oxygen to make sure they recieve the Darwin award.
Most likely not regularily, no, but I for one wouldn’t hesitate to use CO2, Argon, CO2+Argon mix or nitrogen if using those would be beneficial for whatever I happen to be doing with my laser.
But then again, I’m BEng Mech and have almost 5 decades of Gyro Gearloose kind of DIYholism under my belt, so if I for some reason don’t know what precautions to take to do it safely, I do know where to find the information.
Regards,
Sam
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I was very surprised to see how many people with their hobby machines cut metals or other material and use exotic gasses in their use, including oxygen…
I think the statement is a bit large to cover all hobby lasers, some people have, what I’d call, extreme hobbies, including lasers.
I’ve run into them on this site…
In the end, it’s what you’re cutting or doing that determines the gasses or machine setup … hobby or not. I know I couldn’t afford some of these peoples hobby machines.
Back to the brain being where the safety occurs.