I see LB has an option to disable air assist for certain layers.
What would be the reason to disable air assist?
This is useful for operations where air assist is unwanted. For example, on an engraving where air assist would force smoke onto the surface of the material resulting in a dirtier appearance.
Small addition: this only works if you have a laser that supports it. Either the board has a direct pump control port or you have an external relay that switches an external pump. Otherwise, this won’t have any effect.
For the Sculpfun S10, according to your profile, you either need the “automatic air assist upgrade” from Sculpfun or add a custom solution as described here:
A more general answer…
All machining produces some type of debris and may clog the tool bit.
Our tool bit is the lens (really the beam, but). The lens is what make a laser useful.
The number one object is to keep debris off the lens. This really works best when the air assist surrounds the lens area with higher pressure making it more difficult for debris to contact the lens.
The other reason has to do with how it effects the actual material. I believe you always need some air pressure for lens protection.
I have the air opened when my machine is in run mode, this is reduced to a few pounds. It operates with low air pressure normally.
When air assist is enabled, that layer bypasses the air reducer and gives full pressure for cutting, when needed. I run low air pressure cutting acrylic and high pressure with other materials such as mdf.
- protect lens
- deal with debris in other ways not related to the lens
How all of this is handled, is really controller dependent.
Good luck
I’m using a blower from an old oil burner because I was too cheap to get the air pump. It actually has PWM control, so I think I will implement “air assist off = low pressure” like you have.
Do you have an extra pwm output on your controller that is gcode adjustable?
I think most gcode machines use M8 or M9 controls, but I’m not up on it…
Good luck
I am very new to lasers (plenty of experience with 3D printers though), I haven’t looked into Firmware hacking yet. I don’t know what the stock firmware is based on and whether it’s even open source. For my blower I built an adapter that generates the PWM.
In LightBurn I saw only on/off anyway, nothing to set a percentage.
The firmware is based on grbl, which is open source and very similar to Arduino’s / 3D printers (in fact, it also runs on the ramps board or an UNO with CNC shield). The protocol is not that difficult.
Though, most new boards (like the one in S10) use ESP32 chips and therefore a port called grbl_esp as base. Most manufacturers do some proprietary additions, Sculpfun did as well, but not yet in the S10 series. They released most of their firmwares open source (you’ll find all links here: Firmware Update & Settings - Diode Laser Wiki)
Though, supporting a variable PWM output will need more than a protocol change, since LightBurn (and most other tools) only support the standard command which is binary. I don’t think it is worth the effort to integrate this function. Then I’d go for a solution where the air assist always runs at low power all the time and is going to full power when the M8 command is received.
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Thanks so much for the summary. 
If I want to build my own firmware for the S10 would you suggest I go with Grbl_Esp32 or FluidNC? If the latter, is there already a machine config available?
Also today I learned that apparently there is a community converting Atari 1020 plotters to ESP32. 
Personally, I’d go for FluidNC. There is a config on the wiki page I linked above. At least, I think that I uploaded one; otherwise, I can check my archive where it is. I think I tested it at least once. In my opinion, Fluid has the potential to become the next-generation firmware because grbl is not actively developed anymore. It might get the klipper of lasering 
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