Hello Fellow Laser People,
Preface: I am running a JTech Photonics 4.2 Laser on my Shapeoko Pro XXL CNC.
I ran a cut test on 4mm Baltic-Plywood from Menards. Running at 90% power, and if I remember correctly, at 500mm/m. To cut through this plywood it took 18 passes to start seeing flicker of the laser underneath, and 20 passes to be able to push the cut free with minimal strands of wood holding it in place.
My question, is this normal?
Assuming this is about a 5watt laser, 20 passes seem like a lot. I would slow speed down and up the power. Also, you have a cnc so assume also that Z axis is functional. So, I might try moving z down a small amount with each pass.
Air assist if you have it.
Ultimately material tests with various speeds and feeds etc. will tell you what it is capable of.
… I don’t know if it’s normal. With my 5.5 Watt diode laser (Eleksmaker) it is also not possible to cut (usable) through 3mm B/BB plywood.
In some cases, plywood can give bad results even for a 40 or 50 watt CO2 laser.
But under the line, a 4 watt diode laser is not intended for such tasks in general.
Z axis adjustment by how much? Any guidelines?
It would be cool if Lightburn had this function added on the job process with each pass.
The doc reveals many nice features:
Z step per pass. I would move it down as much as depth of cut on each pass.
So it shows the following…
“When doing more than a single pass over a shape, the Z step per pass setting allows you to tell LightBurn to raise or lower the laser with each pass by some amount. This is most often used for thick cutting or deep engraving, allowing you to shift the focus point deeper with each pass to help maintain efficient cutting.”
Question: when doing a cut test and has several test cuts in a row, will it automatically reset to ZERO Focus for each cut? If not, this can cause a real problem.
I forgot to say, everything I’ve cut with more than 4-5 passes (also applies to CO2 laser) looks awful and tons of post-processing time have to be spent.
Please keep in mind I run a 4.2w laser, probably the lowest in the blue diode laser spectrum these days.
I am very much a beginning novice at this time.
Lots of questions and fewer answers currently.
In my version of Lightburn 1.4.05, I show the Z Offset line, but no “Z step per pass”.
Why is that?
Correction, on my laptop it doesn’t show, but on my desktop, it shows.
That’s why I write that you should use the right tool for the right project - or do you waste plenty of time, only to see in the end that you couldn’t cut properly in 4 or 3mm birch plywood. Use poplar tree or some similar softwood.
I am trying to build a material library.
currently I am trying to use a material I have available to me.
One would assume so, but I’d cut a few cardboard test pieces before starting on spendy stuff.
AFAICT, you must understand all the intricacies of Z axis homing and absolute positioning before it will both make sense and work the way you think it should. Hence: cardboard.
Also:
Devoting time to reading the doc will pay off handsomely in terms of both answers and time savings for all parties. 
Sorry about being a pain in the rear.
Reading has never been a strong suit for me. I have trouble sitting still for long periods. If there were an audio or video for docs I could do that more easily.
I’ll try and find answers in the docs prior to asking anymore questions.
Thank you.
Indeed there are, available directly from Help → Online Video Tutorials in your LightBurn window:
Enjoy!
The variety of ply is a huge factor. I finally got really good results after using up a 2’x4’ liece doing a lot of testing so I went back and got a 4’x8’ sheet to start a project. Well, it was a different brand and didn’t cut for sh*t. I have best results on Luan, but the “Revolution” ply is a hard no.
Have you put effort into finding the focusing depth? Attach a 3” wide sheet of your desired material, or maybe something cheaper (I use thin Luan ply) to side supports cut at something like a 30 deg angle and start making single pass experimental burns in the uphill and downhill direction across the ply. At some speed/power setting it will either give you a burn line that tapers from diffuse and wide towards and then away from the smallest burnt dot (hopefully laser is at least focused enough for that) or it will burn through. Measure the distance from the surface of the ply at the best point to your favorite reference point on the laser head. That will give the most concentrated beam available with your machine’s current focusing. If the central dot is not small, then you will need to learn how to focus your laser down to its smallest dot.
Have fun!
What I have done is use brown paper then using a marker make it black. I then followed the focusing directions from the manufacturer to get a pinpoint dot.
Great! If you know the distance to the pinpoint focus dot you have, then try a flatter angle, maybe 15 or 20 degrees, set that distance to the middle of your cut line across the 3” direction, and try different power and speed settings. If your laser will cut that material, you will find what works. I found that with my NEJE 3 max that cutting ability was not linear with power setting. Making one attempt at a cut at a time it did not take me many tries to find a power/speed/distance/number-of-passes combination that cut cleanly through 3mm luan with minimum over-burning at the sides of the cut. I also found that lots of pressurized air on the cut improved cutting and helped minimize over-burning on the sides.
This is definitely a trial and error and then improve kind of a hobby.
Have fun!