Out of focus Cut not as expected

I am attempting to make a small cut, out of focus and it seems to operate differently than what I expected.

I have “Enable Z axis” enabled on the device, and it does make the Z offset, but AFTER the cut is made.
So, in other words the laser moves to the location, cuts with the power and speed settings, and then moves the Z access as requested, then back to Z=0, and then on to the next cut.

Ideally, what I would like to happen is to have the Z shift first (making it out of focus), then cut all of that layer, and then reset Z to zero for the next layers cuts. Is that possible?

According to your profile you have a Ruida. It should make the Z offset move before the start of the cut, and Z-step moves happen after each pass. Which version of the software are you using?

You will also need to set your “Material (mm)” value to the initial height you want to use. Can you show me the cut settings you have so I can check?

We are on 0.8.07, which I think is the latest version.

In this case the material thickness was set as zero, as it is thin material and didn’t think it would make any difference.

It is a small cut, so is it possible that the cut and the Z offset start at the same time? If so, the cut would be done before the offset could complete, as the deck moves a lot slower than the laser. Other than a z offset of -.2756 (in) the cut setting are the same as all the others we use.

The Z move should execute before the remainder of the cut. Which controller model do you have?

When I said you’d need to set the “Material (mm)” value, it’s a bit mis-named on Ruida, as it would need to be whatever your initial Z height is, including the material and the focal length. If you have your focus set, you can click the “Get Position” button on the Move window to see the initial Z value. You’d set the “Material (mm)” value to whatever that registered height is.

Oh. I am still a bit of a newbie in this environment. How would I check what controller model we are using? As to the material value, I will make that change and do some more experimenting to see if I can figure something out. Thanks for your help.

There’s usually a silver sticker on the box inside the electronics panel of the machine. That will tell you for sure. You can also just look at the bottom of the screen if you run LightBurn after the machine is powered. You’ll see something like this:

Just like your example, it shows RDC644XS.
I did some more testing and it appears to operate just like I described. The cut is made, and then the deck is adjusted, down (or up) and then returns to original height.

I’ll investigate this today.

Thanks. In case it helps, I notice that RDWorks has a Pen up/down delay, in milleseconds. I don’t see any similar parameter in LightBurn. I assume that RDWorks uses the Z axis to raise and lower a pen,which wasn’t what I was attempting, but it is an interesting alternative. I wanted to use an out of focus cut to mark fabric faster than a scan.

So I have the same controller (RDC644XS) and used these settings:

  • (Used 4mm thick plywood and auto focus)
  • Layer Z offset -5mm (it says ‘Out’ next to it, so I expect the bed to move downward)
  • Material Thickness 4mm (set in the Cut Info panel)

It works perfectly. Uploaded a short vid of the operation here: https://www.youtube.com/watch?v=oQTKg2F-eyc

(Edit: for those worried about the movement of the laser head: I accidentally had perforation mode enabled on the cut with a 1/0.1 value so that’s why it’s a bit jaggy)

Thanks, I will double check that I have things set up this way. I must have something else messed up.

Be sure to set the material thickness. While I don’t completely understand how and why it influences the Z-offset, it certainly does :slight_smile:

On Ruida, at present, the “Material (mm)” value is used as the starting Z height. It’s misnamed, but I’ll be fixing that shortly. Ruida controllers don’t have the ability to do relative Z moves during a job, so it needs a starting value.

And thanks for running that test and posting the video. Much appreciated.

You’re welcome :slight_smile:
Ah, that makes sense. I’ve notice my machine always reports 4mm as ‘Material Thickness’ (independant of the actual material thickness) since that is the movement made by the auto focus, I suspect.

Couldn’t Lightburn fake relative movement by getting the current Z-value from the machine and offset accordingly ‘under the hood’?

That’s exactly my plan, but it will require being connected, which is a reasonable compromise for the easier workflow.

Sounds good!
There could be a checkbox (labeled ‘Get from machine’) which, when checked, greys out a manual input box next to it. When unchecked, the input box becomes editable for the user. Just an idea, I know i’m probably overcomplicating things :slight_smile:

Off topic: keep up the great work! I received my laser cutter just over a week ago and had only a bit of experience with cutters and software. So glad i bought Lightburn with this machine; the video tutorials are very helpful and the program itself is so intuitive, logical, functional, smart and it allows for a really rapid (iterative) workflow. It makes the laser cutter a joy to use!

OK, I finally got some time to figure this out, and I think I have done so. My original mistake was an observation error. What appeared to be happening was that the cut was being made, and then the z axis was adjusted out of focus, and then back in focus, and then the next cut was made. The cuts and the z offset were both small and the laser was fast.
So… I slowed it all down and have concluded that I was missing the z adjust done at the origin, before the laser even traveled to the first cut. The z axis adjustments done at the end of the cut were the opposite of what I had assumed. They are actually back in focus, then out of focus and then initiate the travel to the next cut. I would have preferred that the z offset be done at the beginning of a cut, not at the beginning of travel to the cut, but now that I know how it works, I can live with it. Thanks again for all of your help.