We have a 50w flux beambox pro laser with an issue after replacing the tube, psu and focus lens and doing re alignment I am having an issue where the engraving isnt super sharp like my other lasers at 500dpi.
Small text is blurry like it is out of focus.
The alignment looks perfect to me, have been laser engraving for about 5 years so I don’t think it is a basic issue.
I’ve tightened up all belts but I still can’t find the issue.
There’s no way to adjust the overscan but to me the dot size seems big at the nozzle exit?
It is about 4mm and circular before it enters mirror 3 and is fairly central.
One thing I noticed which was odd was that if I do alignment at the nozzle exit which I normally do, it’s as good as I can get it. But if I take the nozzle off and just pulse at the ring it looks off centre. Of course if I adjust it and put the nozzle back on it’s then hitting the edge of the nozzle. But there’s no wiggle room with the nozzle and the lens is sat flat and the right way around so I’m a bit lost.
I’ve attached images and the end result. The darker engraving is the laser in question. The other house shape is at 333 dpi and the 2025 is much sharper.
I’m tempted to drop down from a 2 inch lens to 1.5 inch but I know this isn’t solving the actual issue.
I wonder if your beam’s waist (tightest focal area after the final lens) is not coinciding with the tip of your nozzle, causing your beam to get cut off by the nozzle itself. If your beam diameter out of the tube has changed it would change the shape of your focus hourglass
In the red circled area, it could be clipping. There’s also the possibility your final lens isn’t concentric with the tube. I’d inspect that final lens to confirm and run a focus test. Focus Test - LightBurn Documentation
First thing I’d suggest is to ensure you don’t have the lens in upside down. Some of these are very difficult to see and will cause similar burning as it’s not focused.
Kind of the same idea as @Colin mentions, except it sounds more like the beam going down the tube isn’t in the center, the resulting output of the lens will closely resemble the offset of the input beam.
You could have the beam going down the tube off center and it’s correct enough by your lens to get out of the nozzle. This is handy for checking the center of your nozzle. It’s a Russ Sadler creation.
The best possible resolution results from a combination of spot size and material, whichever is worse.
No glass tube hobby co2 laser running a standard setup is not going to have the ability to make a spot size of 0.05mm (508dpi).
I use my 2" a lot and I figure it’s between 0.10 and 0.20 for a spot size. Even most diodes can make about 317dpi with a spot size of 0.080mm.
Best case is 0.10 spot size which under good conditions could produce 254dpi. Most of the time on my co2, I use either an interval of 0.20mm) (127dpi) or (254dpi).
I assume these are supposed to have square corners?
Thank you both for the replies. This first started happening with a tube which was about a year old and i thought it just needed replacing so i replaced it. Then i replaced the PSU as it was humming quite loud and i thought it might be vibrating the machine.
It certainly feels like this diagram. So basically when i take the laser head nozzle out and just do alignment on the Double Threaded Laser Head Socket as shown below, I can get it central no issue.
But then as soon as I pop the laser head nozzle (shown below) in with the focus lens, it then looks like it is just hitting the corner. Note there is no wiggle room, it is very snug.
If i take the focus lens out, it looks fairly central but obviously the beam is quite big so its hard to know if its being clipped etc.
I have two lens (both the same but one is brand new). I ensure they sit perfectly flat inside the housing and then secure it. When i look at them inside the nozzle at the focus lens I am zoomed out. It is a little hard to see the curve on the lens as they’re only 12mm in diameter.
Don’t worry about that, this was done on another laser machine (trotec). The issue i have is the thickness of lines, the font style which uses 2025 is really thick in comparison to the other photo.
It isn’t lightburn supported, but I knew more experienced laser users could help. I am pulling my hair out trying to figure out what is going wrong. (I am a paying lightburn user btw).
I am fairly confident that the issue is still due to this large beam output that I am experiencing. I got this on my old tube and also on the new one. In my head, if the beam output when it hits at the correct focal height is too big surely it’ll never create a nice sharp engraving regardless of the DPI. I have ran a ramp test and verified the focal height is correct
Thanks both, I don’t have access to the pulse power percentage but i assume it is 100% or close to .What i do generally is lower the pulse down by about 60%. When i pulse it normally closer to 100% it looks OK i think.
Going to give that frame that Russ made a go to see how it is at the focus lens.
I have also just been told by their support team that the 2 inch lens should be 12mm focused, but their actual focus tool that they provide is 8mm so this might change things.
Thank you for these Jack - helpful as always! I will do some work and come back to you with my findings. I did use Russ’ tool today and found the alignment slightly off centre. It has improved things, it is not like how it was before but it is certainly better.
I also think I am also potentially asking a bit too much from a chinese 50w laser since we recently got a Trotec speedy 300 with a ceramic tube, the quality that produces is quite outstanding and naturally I am comparing apples to oranges.
RF machines (metal/ceramic tube) generally have a larger beam output. This relates to a smaller spot size. Notice input beam diameter is in the denominator.
Meta tube machines have a response time in the microseconds, compared to a glass tube millisecond response range.
Metal tubes are controlled digitally. When it lases, it lases at 100% power during the pwm on time, otherwise it’s off. Doesn’t seem like much, but most lasers produce a better beam quality, know as M2 at higher power.
Metal tube lasers were a military advancement for mechanical durability and operational dependability.
This is what I would have gotten, if I had deep pockets.
