Laser power getting weaker over several engravings?

Dear all,

I have the following problem:

  • I made the same laser engraving 4x times over the last 2 weeks
  • In the image below, the first engraving is at the top left, second top right, third bottom right, and fourth bottom left (so basically going clockwise)
  • You can clearly see the laser marks are getting weaker with each engraving and various image details are becoming blurrier

Some further details:

  • I am using the same file prepared with Luban

  • Settings were Dot mode, Density 7 dots/mm, Work speed 1500 mm/min, Dwell time 5 ms/dot, Laser power 100%

  • I am using birch plywood, same batch from the hardware store for all four engravings

  • Each engraving takes around 50h to complete (quite long, I know…)

  • I started the jobs with around 1 day in between

  • I dusted off the laser head after each job, primarily to get rid of the fine wood dust created during the engraving process

  • I have been using the laser for quite a while now, I completed some 30 engraving jobs of this type

  • Thinking back of some older engravings (which I have already given as gifts), I believe this issue is not new; I think some older engravings also suffered from blurrier details

So why is this happening?
Is it “normal” for the laser power to decrease in this way?
Could the fine dust be affecting laser power somehow?
Am I missing something here?
And most importantly, what should I do about it?

Many thanks in advance for any thoughts and suggestions! :blush:

What’s the precise thickness of each plywood, with digital calipers to the nearest +/-0.01mm?

In the engraving order I mentioned, I measured 9.03, 9.11, 9.07, and 9.05 mm.
Nominal thickness is obviously 9mm.
I calibrated the laser height with another plywood from the same batch and it came out to 25mm, so overall 34mm z-value.

That isn’t the cause then, those are all very close. Assuming each was located in roughly the same place each time as well so as not to be affected by bed or axis tilt.

I can’t think of a reason the laser would decrease in power - I’m leaning towards believing this is a change in beam waist relative to the piece.

Is the Z height subtly changing over time? Is the focus of the laser changing over time?

Indeed, I don’t think the material itself or the settings are the root cause.

I didn’t re-calibrate the laser in between the jobs, I calibrated it once before beginning and got 25mm laser height which I used for all the jobs.

If the laser were to somehow “de-focus” with time, then indeed the calibration would no longer be correct. I will check tomorrow morning and see what results I get in the calibration.

In the meantime, perhaps @Snapmaker-Edwin or some other staff colleagues can comment… perhaps I simply ended up with a faulty / “less than ideal” laser unit?

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It seems the root cause was the fine wood dust after all.
I unscrewed the laser head and opened it;
As you can see from the photo below there was a massive deposit of wood dust on the fan.
The laser “casing” below had a similar deposit of dust.
The camera and the board were less affected, but still had a fair bit of dust.
I’ve cleaned up everything as best I could, but I’m really unsure on how to proceed…

A few questions that come to mind regarding this issue:

  • Is this caused by the type of wood I’m using?
    (birch plywood, see this site for more information, Google Translate as it’s in German)
  • Or to phrase this differently, is such a level of dust normal for wood engravings?
  • Shouldn’t the laser head be able to “cope” better with wood dust?
  • I mean what happens during wood laser cutting?
  • Has anyone else experienced something similar?

And a few more questions regarding potential solutions:

  • Can I solve this by attaching a big fan outside the enclosure “sucking up” as much debris and dust as possible? (thinking of your setup @brent113)
  • Or should I attach some sort of vacuum cleaner right next to the laser head?
  • Or both?
  • Or do I have to “deal with it” and get used to regularly cleaning the laser head?

Any other ideas and suggestions would of course be much appreciated! :smiling_face_with_three_hearts:

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That looks like CNC dust - any possible way for that to be the case?

Laser dust is combusted and I would expect to be charred.

Nope, I never used my CNC module until now…
Wanted to learn a bit more Fusion 360 before I start delving into that.
Good point that the dust should be more combusted, so no idea why this isn’t the case here.
Again, perhaps the type of wood?!

Buy your wife a new set of pantyhose’s. Use an old pair to make a screen over the inlet. For Lasers, I recommend getting fiberoptic alcohol pads. They are 97%+ alcohol. Just dusting will eventually cause the laser to scar the lens.

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@Rusty_Raine which inlet are you referring to? The “slits” on either side of the laser head?
And I’m not sure how pantyhose or any other mesh-type material could stop the dust from coming in… the dust seems quite fine, so wouldn’t it just slip through anyway?

Yes the vents on the side. You can’t stop all of the particles but you can reduce how much gets inside. Nylon stockings are a really fine mesh. You will want to monitor it to see how quickly it clogs up. If it comes to the point of stopping airflow then the unit could overheat.

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I was only cutting card and saw a very rapid drop off in laser performance to the point where it didn’t make any kind of impression at all. I haven’t taken the laser apart but SM have sent a replacement. My old one is heading back to them for investigation. However the new head cuts way more efficiently than the original one ever did, by a significant margin. Thought is the laser tube failed over a short period.

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@toolshed - Did you contact SM directly over the support email? What sort of “proof” was required to show it was not your fault?

I’m curious whether I might have a laser tube fault as well… the auto calibration marks are certainly not as strong as they used to be, regardless of any wood dust

The fan is flipped and you need to revert it. The sticker should be at the bottom. Here is an image for your reference:

@Snapmaker-Edwin:
I will do as instructed.
But one critical point – the fan was installed flipped like this when I received it!!!

I am now thinking this may have caused additional wood dust to get sucked into the laser head instead of the dust being dispersed away from the head.

With all due respect, this seems to me like a pretty faulty laser head to begin with.
So @Snapmaker-Edwin, I would like to discuss a replacement with you, since the laser strength seems to have decreased drastically, perhaps due to the influence of this dust or perhaps due to some other laser-inherent issues.

Sorry for the inconvenience.

Please PM your order number so that I can locate your order.

Cheers
Edwin

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I just looked up the old order information and sent you a PM.

I have got your PM and will process it today.

Best regards
Edwin