Seeking help regarding laser cutting

Hi Folks,

I’ve been struggling with the laser module from my A350 for a while now. Engraving is fine, but cutting really is a hassle.

The basic setup:

  • I always set Fixed Power to 100% in Luban
  • I use the latest version of Luban and the Firmware
  • I have calibrated the laser several times, the result is always the same.
  • I ve been using both the reference guide as well as resources in the forum

But I am not really satisfied with the result. It seems the laser just can’t cut through materials I’ve been testing:

  • Double Corrugated cardboard (the boxes the SM came in) - Can only cut until the middle layer
  • 2 mm solid carboard (unified material, so no waves) – not getting through with multiple
    (4) passes
  • Plywood (3mm) - No chance to get a clean cut with multiple passes… even tried 20 passes with 0.2mm stepdown

I know that I can get through the materials with a super slow (<80 mm/min) and a ton of passes, but I am striving to get to a reasonable setup that does not require every job to run for days.

what I try to achieve is that I have a test pattern that I can launch in Luban (or have on my SM2) to use with any new material to easily identify the optimal setup…
I’ve been seaching for some patterns and found some (e.g. https://www.thingiverse.com/thing:728579
) but I’m not really confident that Luban is handling them correctly.

any ideas how I can get out of this misery? how do you folks work with the laser and what are you setup’s you use?
Regards,
Markus

The beam waist of the laser isn’t particularly deep, and it won’t cut well outside of a narrow range. Cutting thick materials means moving the laser down before cutting a second pass. You can try this manually by lowering the z-offset between passes.

For really thick materials, in order to allow adequate laser light to get to the cutting region, you need to burn away a V-groove. The angle can be close to vertical, but it cannot actually reach vertical. Insofar as I know, this still requires custom path generation. It’s also worth noting that the cut time will have to increase quadratically with material thickness.

Hi @eh9 ,

thank you for your response. I think it is a good insight to keep in mind that the laser would require this shape with deeper materials.

But I’m talking about e.g. 2 mm solid Cardboard that according to the guide should not be a problem at all.

What you should learn from what you have seen yourself is that the effective cutting zone of the beam waist is less than 2 mm deep.

You would do well to keep in mind the very large amounts of puffery that the manufacturer engages in. These machines were oversold from the start and continue to be oversold. Please look at what your machine is actually doing and ignore the innuendo that the guide says it ought to be doing.

Hey @eh9,

you are probably right about the @staff overselling their product. At least since it does not seem that they are eager to get these very basic issues under control by keeping their documentation updated and their users fed with new information.

The corrugated carboard from here https://support.snapmaker.com/hc/en-us/articles/360019025954-The-Definitive-Guide-to-Laser-Engraving-and-Cutting-with-the-Snapmaker

1mm carboard is listed as 2 passes, and 3mm is listed at 2 passes, both with 0 depth.

In my experience as well that is usually not going to work. I’ve found a maximum effective cutting height of the laser to be approximately 1.5mm AT MAX, usually less (speed dependent), and that’s only going to work if the waist of the beam is perfectly centered in the material. It’s much easier to just do step downs of 0.5mm or so and do multiple passes as a higher speed. Will result in less burning as well.

Interesting @brent113, so you would not consider the step down too much an just have it fixed at 0.5mm? In the past I calculated the material height and decided this by the steps I deemed right and rounded this to make it through the material… will try to fix the step down and do some testing

I don’t have a lot of experience in optimizing steps for cut speed and quality, as I’ve mostly been doing engraving or cutting paper. I think if you have something that’s working that’s great. If it’s not working, try more smaller step downs, or traveling slower.

So I dedicated 4 hours to this and got some positive results and potentially an idea how to optimize the setup further:

I created 3 squares each 10 x 10mm and added the text for speed and passes around them (so I can document the settings i used). I kept power at 100% and stepdown at 0,5mm to be consistent.
With this I started testing different speeds and amounts of passes until I got a clean cut (Speed 100, Passes 7). :heart:
Now I wanted to optimize the setup and here I think I realized something a person with a basic understanding of mathematics and physics would have realized faster :roll_eyes:

It is more important to increase the work speed than striving for a lower number of passes
is that really right? In the beginning I thought it is the complete opposite since any additional pass would add significantly to the overall duration of the process…

Here is my super basic calculation, Google helped me (or misled me):
formula of one pass:
t=d/v (with t=time, d=distance and v=speed or velocity)
To calculate the overall time with multiple passes I multiply with the amount of passes.
I ignore any movements between the passes for sake of simplicity.

With my basic square of 10mm i have a distance of 40mm
The first successful cut was at 100 mm/min with 7 passes --> 2.8 Minutes overall duration
After some testing I stopped at 160 mm/min with 8 passes --> 2.0 Minutes overall duration

I have not tested 180 mm/min with 9 passes (8 passes was not enough) which would also lead to 2 Minutes duration. Interesting to see that the speed needs to be significantly faster to make up for one additional pass in these cases.

Maybe some of you can’t stop laughing but for me this is a significant success… my teacher would be so proud… :rofl:

Am I completely wrong or is that a correct calculation…

And is there a better way to find an optimal setup or does it have to be a trial and error thing?

Why is it relevant to optimize?
Since I want to do larger and more complex cuts, it is important to find an optimal configuration… if a single pass takes 30 Minutes instead of 60 minutes I would say that’s significant. with a path of 6,000 mm that would be the case with the 100/7 settings instead of the 160/8

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What you want to maximize is power transfer efficiency. The laser has a fixed power output, so you can’t do better there. What you can do is to make sure that as much of that laser power as possible goes into cutting. Remember the physical process you’re doing: heating up material, first driving off gases, then burning off the remaining content.

  • When the beam waist isn’t in contact with anything, you’re wasting power. So moving too slow can be a problem. Also a problem if the beam waist is too high above the cutting zone; it’s why you want to step down.
  • When the beam heats material up but doesn’t remove it before moving on, you’re wasting power. The material will have cooled off by the time the next pass comes around. So moving too fast can be a problem.
  • If the beam is occluded before the waist, you’re wasting power that doesn’t get concentrated into the cut zone. This is the reason for making V-shaped kerfs as I mentioned above. I haven’t done the experiment myself yet, but I think this effect probably starts as soon as you need more than one pass to complete a cut.
  • When the beam is partially occluded, the remainder of the beam is less powerful and needs to move more slowly. If you’re not making V-kerfs, later passes should probably move more slowly than earlier passes.
  • When the beam is shining on white material (high albedo), it reflects more energy than the same beam on dark material (low albedo). The first layer may require a lower velocity than subsequent layers.
  • When cutting wood and paper, you’re burning away material. This works faster with constant replenishment with oxygen. Warm oxygen is even better. If you’re interested in designing a useful mod, take the air that passes over the heat sink for the laser diode and direct it onto the beam waist. If you pump too fast, you’ll cool it off more than cause it to burn faster.

There’s still some trial and error involved, but I hope this helps you think about how to interpret what you’re seeing.

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In addition to all of that I’ll add that as you reach higher and higher speeds you will become jerk limited. The maximum attainable speed is limited by machine acceleration and a function called junction deviation.

I agree with your math. Much more sophisticated math would consider the maximum acceleration the machine is allowed given the configured junction deviation tolerance around the 90 degree corners.

Except for academic reasons it’s not worth trying to do that math. Suffice to say at some point the sharp corners will become the limiting factor, and maximum attainable speed depends on the specific model geometry.

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I’m also cutting 2mm cardboard (1100gsm), to make a 3D map.

In Luban I generated G-code using 3 passes with pass depth 0.5mm; jog speed 1500, work speed 120.

It cut the cardboard just right I think, but there was some black carbon dust/soot. Enough that I got some on my hands and the cardboard as I pressed each shape (about 50) out of the sheet.

I guess this is inevitable? Its cutting after all… or does it suggest I could speed up the jog or work speeds? The job took 6 hours (2 hours per pass).

You didn’t say what your power was. I’m assuming 100%.

I just did some puzzles out of 2mm poster board with photo paper attached using spray adhesive.

While I found I could cut through at 100mm/m with 3 passes I found the least char/soot was running faster with more passes. It ended up being a tricky balance to still cut through and not leave visible marks. My final settings were around 300mm/m and 12 (15?) passes. I always have jog speed at 3000.

My wife and daughter loved the puzzles and while you couldn’t see the burn on the photo when the puzzle was assembled, it did turn their fingers and the puzzle board black. In the end there was no way to not get soot and still cut through.
If I try it again I’ll use a drag knife.

-S

300mm/m, 12 passes, and how deep each pass? I’m looking for a faster way to cut cardboard, I had 2.2mm, with 5 passes at 0.3, and it took almost 4 hours, and I cut plywood in under an hour. I understand I had 5 passes (too much?) and I think I could increase the cutting depth to 0.7 ish? I will try now and see

How thick of cardboard?
Not sure on cardboard because it’s partly hollow, but on ply you set the depth depending on the number of passes. Divide thickness by number of passes. So 2mm at 4 passes would be .5. I usually add a pass for good measure.
Everything cuts slightly different so just have to play around. You are running 100% power?
It’s not cutting depth, it’s focus depth. So you want each pass lowering itself by the amount of material removed so that the optimal focus matches the new surface height. That can be the hard thing to figure out.
-S

I have found that a .5mm CNC endmill is much easier to use for cutting material. I first laser the graphics, then switch heads and cut out with the router.

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Good post, I also found that multiple passes faster are better for wood. I was making some Christmas ornaments out of 1.5 mm plywood, and was having a really hard time following the snapmaker guide with just one pass. It would cut through only about 40% of the time and show substantial burning. I switched to two passes with 0.4 mm lowering between the passes, and up’d the speed. It worked perfectly with about 95% cut through and clean edges without much burning.

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FWIW, I’m cutting 3mm corrugated cardboard with 2 passes at 130mm/min, 0.6 step down, 100% power. From memory, the outer box of the snapmaker was two layers of that - yeah, I can imagine that would be a struggle.

And I am wiping everything with a dry cloth afterwards to get rid of the soot…