Laser Diodes----Under the Hood 18 

I agree. My understanding of air assist is to stop soot landing on the lens and causing damage as seen at 2:36. I would have an air filter on the air intake too.

Hi Marcus I really appreciate your interaction with this air assist issue and some of the things you point out are relevant. However. I have spent many years with CO 2 lasers and fully understand the reasons why and when not to use full air assist. In general, you need air assist for cutting to blow the fumes oiut of the BOTTOM of the cut because with CO2 you never try to use multi cuts. If there is no bottom way for the fumes to escape they, by default, must run along the blind kerf and rise out of the material surface whereupon they meet a downward rush of air assist ( or in this case the significant cooling airflow) and stick to the edge of your cut. The fumes are not solid particle but micro droplets of hydrocarbon tarry substances (like steam) that will condense on your work if blown downwards. If you can't cut in one pass then it is better to let those fumes rise out of the kerf and carry them away with cross flow air before they get a chance to settle. Yes you do need to protect the lens (or in this cae the protective window) but it requires only a small positive pressure inside the nozzle to do so. Because that nozzle orifice is so large (about 6mm) there is never going to be a JET flow to aid cutting i.e. forcing large volumes of air into a kerf that is about 0.1mm wide. Thus the resason for the nozzle must be just for lens (protective window) protection. Yes, fumes do absorb laser energy but not to the extent you imagine. If you Google the absorption spectrum for various hydrocarbon products you will find that they are maybe only about 20% absorbing at 450 nm So, although it is a sensible precuation to get them out of the cut area as quickly as possble it is not a huge issue because the wood you are trying to cut is even less efficient at absorbing 455 nm light energy (about 10%!!!). However, use that 10% absorption to create a surface carbon film and all of a sudden the carbon is almost 100% receptive to 455 nm wavelenght light and so the cutting process begins.This is a completely different cutting mechanism to that which occurs at 10,640nm with CO2. The problem with many myths and ideas about air assist is that they are not rooted in fact. One good example is the risk of wood cuts catching fire. Remember I mentioned the carbon cuttinig mechanism, well that leaves a film of carbon on the kerf walls. If you observe your cuts carefully you will see the walls glowing red as the laser beam stimulates the carbon. Let me ask you to carry out this simple experiment. Take a piece of kitchen towel and twist a corner into a littl sausage shape. Light the end and wait a few seconds before blowing out the flame. You are now holding some glowing carbon (as per your kerf walls). Now try adding air assist (blowing on it) and then ask yourself about the wisdom of blowing on glowing carbon? ( "cools down the work piece"?) I will be devoting a complete session in the near future to the way that air assist works with a diode lasers because as the power increases so single pass cutting become more viable. Fitting a flame detector to your machine is like putting a sticking plaster on a broken leg. Understanding how and why a fire can start, allows you to adjust your usage stategy to avoid the risk.

If there was any movement (wobble?) then I would expect to see it on all the other "spots" a maybe fuzziness or ovality.. At this point in the testing I had no notion of how the individual optical paths were arranged but I would say its more likely that there is insufficient intensity in two of the diodes to complete the doughnut, Hence the C shape. In practice it is never going to be an issue because who would use the beam 10 or more mm out of focus? At the time of making the video I did not consider the "lazy" diodes idea so thanks for your suggestion because my thoughts may still be wrong. Everything I do is new and unrehearsed so you are live learning with me.

Thanks. It somehow makes the word what it is. I'll leave it as is.