I asked about the compressor because if there is once in a while a small bit of water with the air it will “explode” in the nozzle and affect the lens and the mirror, but, it is only a vague conjecture.
Another possibility, is it conceivable that your laser beam hits the inside of the nozzle, just quite a bit?
I have one of the standard aftermarket (Light Object) air assist heads for k40. I didn’t see any moisture inside of the nozzle cap. I did an alignment of the beam with tape over the tip and the beam hits it dead center in all 4 corners. The condensation from the compressor is a good point, I will double check that just to make sure, maybe some water remained on the lens when I took the air assist off.
I hope you find a problem solution. But it will surprise me a lot if it is not reflections of some kind.
So far it has been working great, so the problem is technically solved. The solution itself was unexpected and I still cannot explain it. It does indeed look like a reflection problem, but I’ve gone over every possible step to resolve this mechanically.
I hope this thread helps someone in the future, those K40 machines are strange little things.
Thank you for your input, this is all valuable info.
I have the same problem and haven’t been able to solve it yet. It’s also a K40, but heavily modified (basically a complete rebuild to a 600x300 bed). Similarities between your setup and mine:
- K40
- aftermarket LightObject blue head
- GRBL board (Awesometech Mini Gerbil)
I get the same random dots on a variety of materials. It’s the most obvious on acrylic.
I know this is an old thread, but today I did a test again on thermal paper and the problem seems to be worse than I thought. the dot’s don’t show up on acrylic, or regular paper, only on very sensitive materials. I’m starting to think that this is a power supply issue. This started happening around the time when I replaces the stock PSU with a LO 20W~45W PWM CO2 Laser Power Supply. I’m gonna try contacting them and see if they’ve run into this problem.
1 Like
Hello very good idea to use a termal paper, I will try too !
We have discussed it before, a laser beam can not divide into several different directions, it is not physically possible. That it is so clear on thermal paper shows that it is hot water, not much but water.
But of course I’m not right if you do not drive with compressor air at all.
Sur, isn’t a laser beam divide but perhaps a signal perturbation on the bad quality power supplies or bad shield wire grounding.
No, - how should these “acids” get out of your Laser tube ?, put a piece of thermal paper in front of mirrors 1 shoot and see the result.
good luck
If the power supply fires a short pulse while the laser head is outside the area where it should fire a pulse, then these dots will appear. So it is totally possible to have these dots outside the engraved areas as the laser head moves over these blank areas.
1 Like
ok Gerrit, I’m just asking do you drive with compressed air or not?
I used to use an aquarium air pump when I had the problem with the dots. I now use compressed air with an inline moisture filter. I haven’t checked yet if the dots are worse or better, but I’ll check next time I run an acrylic job.
Quick update, after spending all day with this thing instead of working again, it has been narrowed down to the power supply. Like I’ve stated previously, I’ve ran every possible test, it is definitely not water.
I got in touch with LO support and at first they said that it was noise interference. I replaced the signal wires with shielded / grounded ones and even ran them through a pair of ferrite beads. The test came out exactly the same, so the noise is not the issue. then the tech asked me to do the same test pattern, but shorten the line distance of the 150mm/s grid by half. If the dots are as bad at 150mm/s with distance of 2.5mm between the lines as 300mm/s with 5mm distance, then it is most likely the power supply. They told me to return it which is what I will be doing.
They didn’t offer to cover the shipping and when I bought the supply I already paid $60 for expedited service, so I will order an Orion PSU (same company that made the LO supply) from Amazon for a hundred and send this one back to LO.
I will post an update once the new power supply is installed
1 Like
Yeah, I ran these tests without the air pump engaged. the dots that you see outside of the engraved area are proportionate to the overscanning at higher speeds. Ruida does this automatically when you set your acceleration speed. The faster you set the engraving speed, the further out your head will travel to prevent overburning at the edges.
1 Like
Does that mean that the laser head has been physically above each point? It is very confusing, especially when you do not have air on. I was so sure of my theory. But, the most important thing is we learn something new and you will hopefully soon solve your problem with the new PSU.
I can see in the last picture that the dots stay within the lines and numbers, nothing below or above, I was wrong! 
Well,
I’ve replaced the power supply yesterday and nothing has changed. The only thing that is left is the tube. This is a brand new tube and I have never heard, or seen a co2 tube firing at will like that. Could it be building up a charge like a capacitor? What is interesting is that the effects seem to be worse at high speed/low power, if I turn up the power to 50% it goes pretty smooth.
That’s really an oddity. It seems unlikely that it’s the tube itself producing that, but who knows.
Could there be any loose or mis-routed wiring or anything running on the same circuit that’s causing noise or static in the control hardware? Laser is grounded how?
the entire case is grounded, I’ve checked continuity between the chassis and grounds on all power supplies and all of that is sent to earth. I tried running it with the ground lifted from earth without any changes. I’ve also lifted the ground from motor and controller PSUs thinking they could be adding noise, but nothing changed then. I just watched the tube itself while running the engraving and I do see some abnormal spikes here is a video