Air-Assist Analysis Reveals Most Effective — And Quietest — Methods

If there’s one thing that continues to impress us about the Hackaday community as the years roll by, it’s the willingness to share what we’ve learned with each other. Not every discovery will be news to everyone, and everything won’t be helpful or even interesting to everyone, but the mere act of sharing on the off chance that it’ll help someone else is really what sets the hardware hacking world apart.

Case in point: this in-depth analysis of laser cutter air-assist methods. Undertaken by [David Tucker], this project reads more like a lab writeup than a build log, because well, that’s pretty much what it is. For those not into laser cutters, an air assist is just a steady flow of air to blow smoke and cutting residue away from the beam path and optics of a laser cutter. It’s simple, but critical; without it, smoke can obscure and reflect the laser beam, foul lenses and mirrors, and severely degrade cut quality.

To see what air-assist methods work best, [David] looked at four different air pumps and compressors, along with a simple fan. Each of these methods was compared to a control of cuts made without air assist. The test was simple: a series of parallel lines cut into particle board with the beam focused on the surface at 80% power, with the cut speed slowly decreasing. It turned out that any air-assist was better than nothing, with the conspicuous exception of using just a fan, which made things worse. Helpfully, [David] included measurements of the noise levels of the compressors he tested, and found there’s no advantage to using an ear-splitting shop compressor over a quieter aquarium air pump. Plus, the aquarium pumps are cheap — always a bonus.

Not sure how to get up to speed with lasers? Laser Cutting 101 might be a great place to start.

19 thoughts on “Air-Assist Analysis Reveals Most Effective — And Quietest — Methods

  1. The 1/6 HP Airbrush Compressor from Harbor Freight with a regulator on the K40 has been my go to although the regulator is so wide that it makes it useless. But with a quick connect I can throw the larger compressor on to allow the smaller one to cool down and the regulator is definitely needed if you don’t want to blow your material off the bed.

  2. Low pressure solutions are best, where condensation does not happen in the line. If fed off a conventional compressor, either use luck to avoid high humidity days, or some sort of desiccant.

    For an experiment, I tipped 2 kg of silica gel into the tank of my compressor. Ran it for a good month or so with occasional inspection. Eventually looked a little saturated but still poured well, so added another 5 kg of dry silica gel to what was already there. Eventually I’ll have to dry it out, and being a +oil compressor, it’s not going in the oven.

    Kind of fun making a poor man’s desiccant dryer.

    1. Interesting, I’ve never had problems with condensation really, though I guess the UK while renowned for being damp is actually pretty constant and rarely truly high humidity… (I do keep a regulator that is fairly good at catching stray water/oil in the line at the end of the primary hose.
      Not sure if silica gel is the best idea, its going to be hard to remove it from the tank I would think, well harder than just draining out whatever water condensed in there…

      1. Oh my tank is also pretty big, think its 200L (so I often fill it and just use it turned off, as for anything but the die/angle grinder the tank lasts about as long as I have energy to do anything, which will help then…). The big tank should help condense more of the water in the tank safely away from outlet.

    2. My old hackerspace probably had the few laser cutters in the world that had never caught on fire, but did have a flood. I know which one I prefer :)

      It was fixed by adding a big radiator (keeps the newly compressed air cooler so more water condenses in the tank instead of getting through to the airline) and an automatic drain valve onto the compressor, and occasionally disconnecting the airline and blowing it out.

  3. Maybe a duct in the fan could improve things somehow. ?

    I wonder how would be the effects if one could couple even some fans sucking the air out of the laser bed with this cheap pump blowing air at the cutting point …

    1. A fan can, presumably, only blow the smoke away from the surface. Whereas some pressure forcibly directed down the beam, might well clear further down the cut.

      Different gasses could be interesting. Perhaps pure fire proof nitrogen, or extra volatile ozone :)

    1. And it will have the benefit of not deflecting the cut any! The accuracy benefits alone are probably worth the effort.

      I could continue on with how that benefit is frequently (and probably greatly) underestimated by many people, but the same benefit is realized with all of the air assist methods, and I did feel the need to explain I was serious only in my jesting. Since the comments are often not real time, it’ll be interesting to see if the serious benefits are disputed.

  4. I used coaxial gas assist with a small orifice on my latest laser cutter build:

    Compared to the chinese systems I have used that either use an off axis on axis but large nozzle the small nozzle works much better. I run air through a SMC air dryer system which makes very dry air.

    There are some papers on this subject too, I thought I had one bookmarked but I cant find it. If I remember right nozzles that create a hypersonic flow are the best and it has the equations to figure that out. Ill have to look some more.

  5. Seems to match my own tests with K40 laser, where I found that about 50 L/min (2 CFM) is the sweet spot. Increasing 20 L/min -> 50 L/min had a significant improvement in quality, but 50 L/min -> 100 L/min made a much smaller difference.

    For many compressors it will help to adjust the pressure switch to a smaller tank pressure. Pumping the tank to 6 bar is unnecessary work for the motor when the output line needs only 1 – 2 bars to force the air through.

  6. I’m reminded of an anecdote a college professor shared about early laser eye surgery. Apparently the beam used to work from one side of the eye to the other, and they found that the debris was spoiling the accuracy of the correction by the time the far side of the eye was reached. So they modified the process to alternate, working in small increments from each side and meeting in the middle. Perhaps some of that technique would be helpful here.

  7. So…would a simple blower fan work…I’m thinking on the order of a shop vac, but slower and more worried about flow than pressure.

    I’ll need to look into this when I get my full sheet system built this summer. I have an old blower from a van heater system. I’m thinking about having it blow into a 5 gallon pail, then running a 1 inch line out to a small nozzle at the head. Probably a 1/4 inch opening. Lower pressure but high volume of air.

  8. A couple comments. First, don’t get pressure confused with volume. For air assist you need relatively low pressure but a high volume of air. Very much like a plasma cutter.

    The other thing and this is something I have been meaning to try, next time I need to get mig gas I want to get pure CO2 as I don’t want to waste argon, but I want to see how CO2 works for an air assist gas. It seems in thicker things the normal air assist literally fans the flames. It would be interesting to see how it works if it did not add to combustion.

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