A while ago I built myself a DIY 3D printed CNC machine called the MultiBot. Recently I picked up a NEJE 30w laser module and have been trying to explore how to use this diode to the best of its abilities.  Air assist has come up and I have been struggling to work out how much air I really need.  I have a Bostitch 6 gallon pancake compressor that is capable of 90 psi, so I have plenty of air available.  However this is a ridiculously loud compressor and I need to wear hearing protection when operating it.  So I am on the hunt for something that is almost as good but much quieter.  

You can pick up my latest air assist nozzle from Thingiverse.

I would also like to maximize the efficiency of the diode (get the deepest cut) as well as make sure the cut is as clean as possible and finally to do it all with the lowest cost and least noise. I decided to do a shootout with all the air pumps and compressors I have access too.  

  The air sources I tested were as follows: 

• Bostitch 6 gallon pancake compressor set to 15 psi ($150)
• Simple Deluxe 1189 fish pump compressor ($45), 
• Sunrise (DeVilbiss) model 46502 compressor/nebulizer (recycled)
• Aqua Culture 20-60 gallon air pump ($15)
• 24v radial fan from an ender 3 to see if an air compressor is even needed ($1)

First for the noise, I just happen to have a Pyle dB meter laying about.  I measured the dBA right next to each compressor as well as 5 feet away, all within my enclosed garage.

I also measured the max PSI each compressor could produce when no air flows, as well as the PSI when air is flowing unrestricted through my 2 mm nozzle.  Previously I had measured the CFM of the Sunrise and Aqua Culture air pumps along with my compressor.  The results are summarized below.

The ambient noise in the room was hovering between 30-50 dB, any measurements below 50 dB are probably not very accurate and can be considered basically inaudible.  

The Sunrise compressor is capable of producing a surprising amount of pressure, but once you let the air flow the pressure falls dramatically.  That plays out below with it not working as nicely as the simple deluxe air pump.  The big news is that the simple deluxe manages to be significantly quieter than the Bostitch.  It can't compete on the pressure level but if it can get the job done it will be great.

The next step was to evaluate how each works when pushing air through my over the lens nozzle with a 2 mm orifice (or blowing at the side in the case of the fan).  To test this I wrote a program to draw a series of lines, focused at the top of the work piece at 80% power and at speeds from 400 mm/min to 50 mm/min in steps of 50.  The test pieces are shown below.

Looking at these results, the radial fan is worse than no air assist.  It blows the smoke back onto the workpiece and just makes a mess. No air is not very good, even the fastest cut on the left side has a lot of extra scorch damage.  The Aqua Culture pump is where we start to really see the value of air, it is more than enough to improve the lines as long as the laser is moving fast enough that we don't start a fire.  However at slower cutting speeds (deeper cutting depth) we still see a lot of scorching.  The great news is visually the simple deluxe pump is almost as good as the compressor at 15 psi.  We know from previous tests that the compressor at 30 psi cuts even better, so the compressor is always the winner but a $45 aquarium pump is both dramatically quieter...