[ELaser]

Depending on your laser, you may have seen any of several variations on this.

"Air" may also be a generic term, mainly it means literally what is says, the air we breathe, but you can use other gases, such as oxygen or nitrogen to promote or reduce burning / combustion.

I was going to say that at the cheaper / lower end of the scale, the air assist doesn't come though the lens nozzle assembly, but then I thought of Epilog, which can only be called cheap by comparison with a fully loaded and accesorised Trotec.

The *right* way to do it is however to have the air assist come out of the lens nozzle assembly, which not only keeps the lens cool and clean but also keeps the force of the air pressure at 90 degrees to the work.

Most cheaper lasers will come with an air assist compressor that was really built for the aquarium or pond aeration trade, and to be thoroughly fair to the suppliers, this is enough in most cases, for example acrylic cutting, you only want a small flow of air, and even a pond pump with a wide open valve can generate too much air, and do too much cooling, and you end up with smoky white cut edges on the acrylic.

When you start pushing your laser harder and start cutting organic materials, (wood, MDF, leather etc) then it's all change, and for most of us all you can do is open the valve all the way and let the full capacity of the pump dump into the nozzle, and you get what you get.

But if you're serious about this stuff, you want shop air.

#1 you want a pressure regulator with it's own adjustment valve, pressure gauge, water trap and filter, these are a lot less expensive than you think, set it to 20 psi

#2 if you're cobbling together your own compressor you want as big a high pressure reservoir / tank as you can fit, it takes longer to fill, but the compressor cycles less, I know someone who made a really neat one out of a 5 foot high portable propane bottle with a repurposed 0.5HP electric motor driven piston vacuum pump sat on top, just add a pressure controlled mains switch, an on / off switch, pressure release safety valve, water drain valve at the bottom, and some hammerite paint and it works a treat... he actually has his welded to a steel sack truck, he can pump it up, push the thing across the yard to pump a tractor tyre up, or do what his main use is which is spray painting... obviously the 0.5 HP isn't going to give anything except intermittent use for air tools.

#3 if you've got a solenoid controlled on/off air assist valve, make sure it can handle 2 bar (1 bar = 14/15 psi) I've seen a few shipped that not only leaked like a sieve at anything over 10 psi, they actually broke at 30 psi, if you have got what I have, which I personally prefer, the manually turned needle valve, you're golden.

#4 unless you have hugely expensive professional metal cutting kit, it is probably quite dangerous and certainly very damaging to the laser to run anything over 20 / 25 psi.... the full unregulated tank pressure from my compressor with a blocked nozzle will put enough pressure on the focus lens to lift about two thirds of my body weight, I actually tried this experiment with a NON blocked nozzle and shop air at tank pressure and a piece of laser cut 2 mm acrylic in place of the lens... I'm glad I cut some 0.5 mm teflon ring gaskets for the lens prior to doing this, as the acrylic shattered and tore out the original teflon gaskets

#5 don't throw away your pond pump compressor, I personally think its better for the low pressure stuff, so now I just use one or the other depending on the job.

The video below was made by me to highlight the dangers of fire with air assist and cutting wood etc and making scrap.

It was shot with the "pond pump" compressor, which I'd eyeball out at somewhere between 5 and 7 psi, and the nozzle needle valve wide open, and you can see the "blowtorch" effect (and hear it) when the laser cut wood ignites at various places.

With the "shop air" and the regulator set to 20 psi this doesn't happen, the wood IN the cut and being cut gets an ample supply or shop air and therefore oxygen to support combustion, and to keep the cut clear, but it's "too" ample, so it is in constant flameout / quench mode, and the cuts in thick woods etc are that much better because of it.

With the "pond pump" I can cut cheap 16 mm pine board easy enough, but it won't look at 18 mm oak boards, with the shop air I can cut 24 mm oak boards better than the pond pump air can cut cheap 16 mm pine boards. This isn't a question of not enough tube power, I'm at about 30% of tube power to cut 16 mm pine, I can go up to 75% of tube power and all I get is orange glows of light travelling along the grains of the wood internally, it's NOT about not getting enough energy into the wood to cut it, it's about getting the vapourised wood away from the beam... think wrong saw blade tooth pattern / form getting clogged instead of cutting and shedding... more power doesn't help a clogging saw... the correct blade does.

As an aside and a return to the beginning, with 22 psi argoshield (argon gas mix for mig welding) as the assist gas I can cut 24 mm oak boards and the cut sides are as clean and clear as the top surface, it's very impressive but it uses gas like an oxy torch uses up oxygen bottles.

If you've got 100 watts and good optics and a nozzle that is real close to the work when in focus and feed in oxygen at 20 psi you can cut thin steel clean and lovely, got a friend in Germany who did this with the exact same machine I have, it worked so well he had to go out and buy a new honeycomb table... lol

HTH etc

[HomerSimpson]

I have been trying to get more power out of my machine. I have an 80W GWeike. I have run several experiments now with the following variables:

1) Air pressure (10 to 80psi)
2) Location of air knife relative to laser spot (through center of cone or to the side)
3) lense focal length (50 & 100mm)

My baseline config is 10psi through the center of the cone with a 50mm lense. I'm cutting acrylic at 85% power and a fixed velocity. I change my variables and then measure the depth of cut through the side of the acrylic. The only thing that makes a difference is the focal length. At the longer length, the cut is less deep. The other 2 factors make zero difference. I know I'm only using shop air, not pure O2, but what am I doing wrong, given the various comments about how increasing air pressure helps so much?

[ELaser]

"....for example acrylic cutting, you only want a small flow of air...."

[HomerSimpson]

[QUOTE=ELaser;1663244]"....for example acrylic cutting, you only want a small flow of air...."[/QUOTE

My test results suggests this factor is irrelevant. Please either provide hard data to the contrary or suggest to me how my test is flawed. Conjecture is just that.

[rayscott]

I would guess that your 100mm lens does not have such a small spot size. It is typical that as the focal length gets longer, the spot size also gets larger. If the beam spot size is larger, then you need to cut away more material to get the same depth as the 50mm lens went. I recommend many of my customers purchase a 63.5mm lens to try cutting slightly deeper than the 50.8mm lens typically goes. As the target material gets less dense (like foam, sponge, and Styrofoam).. then you can use longer FL lenses and fatter spot sizes.


..and then adding air will help too.

[HomerSimpson]

Thanks for your reply. I tried my experiment with the 50mm and 100mm I quoted originally, as well as with a 190mm lense. None showed an effect. If you think a 63.5mm lense will have an impact, it suggests a massive non-linearity in the effect, given that the lenses that bound it, 50 and 100, show no effect.