LaserUser.com Forum (formerly RDWorksLab)

I have been derping around with my laser for a couple days. Just got it this past week and nearly zero experience.

I have skewing on on etching (x-axis) but not always. It seems to be dependent on the power I'm using on the laser rather than speed, i.e. with same speed, low power etches fine, medium high power makes the etched image skew on a clean angle, high power makes it skew irregularly. It does shift like it's missing steps. Seems odd. I need to do a little more systematic testing even to determine what is happening when, but this laser power-dependent skewing baffles my troubleshooting ideas, so I thought I'd toss it out there in case anybody has ever heard of it. It does seem to low speed cut nice and straight and doesn't lose steps even though cutting is also at higher power, so it's related to speed but not entirely I guess. Head-scratcher.

Speaking of cutting, it changes dimensions depending on the location the head is on the table. I did a cursory beam alignment before doing anything with it and it seemed pretty close when I was done. What I'm noticing is cutting a couple long shapes of identical size (about 8" long) end to end, the piece on the right cuts out about a millimeter longer than the one on the left. Repeating the cut path, it accurately follows the same path so it's not skipping steps.
The only hypothesis I can think of is that my beam alignment wasn't as good as I might have thought. Meaning the only thing I can think of to make this happen is as the head moves over 16 inches or so, the beam might be shifting from one side of the lens to the other, thus shifting the beam as it goes? Does this seem plausible? I've never heard of this but I can't think of anything about the drive system which would cause this.

Sorry if this is confusing. I'll check the beam alignment again, but I thought I'd present this hypothesis on the beam alignment shifting the location of the focus just to see if it seems maybe plausible to anybody else. And yes, the power may be varying too due to misalignment, but so far I'm just cutting rather thin material so it might not show up yet.

So step one will be beam alignment check since that's a pretty standard thing I guess. If that works, I need to dream up a test to reveal what my drive might need for tweaks.

Anyways, any thoughts are welcome. I'm kinda feeling dogged out due to a short stream of perplexing things that aren't dovetailing with more common issues that I've heard about. Please feel free to toss a thought at me even if it seems like goofy spitballing. I need some ideas.

Thanks.

1. I would check the lens is snug in side the tube
2. Check the laser head is not loose - -it should not twist or skew with moderate force by hand
3. What speed are you engraving - over 500mm/sec will cause problems on most chinese machines

Thanks for the tips. 1 & 2 are not things I would have thought to check for a while. 3 I'll look into. I installed RDWorks with imperial units at first and it took me until yesterday to find where they hid the checkboxes to switch the units, so I'm not sure even where I was on the speed. I've been watching a lot of Russ vids so mine seems so dang slow compared to what he regularly runs, I don't have a realistic frame of reference in my head yet. I'll check that out.

Separate problem: I tried about two dozen ways to try to import a CAD file into RDWorks yesterday and found absolutely no love. I'm thinking hard on going ahead and surrendering to Lightburn. That's inevitable at some point anyway, so I guess I might as well get it over with.

Convert files in to an *.AI format - AI import very nicley into RDWORKS.
LIGHTBURN is very good software and is support by a guy who lives in the US -he is the authors and developer and has a website he responds to questings in .....as well and here.

I'm really baffled by my "off-dimension cutting" issue. I don't even know what to call this.

First I did a more in-depth beam alignment. One mirror needed a minor tweak, and the lens tube assembly was tilted front/back a fair amount but was nice and square left/right. Both issues were remedied and the beam seems to be centered on the target all around the table.

So I did a minor test which seemed to make sense, but in the end it told me nothing. My test was to cut some 20mm x 20mm squares about 3 inches inside the four corners of the table. They cut out and I measured them with some calipers. Note that I'm a machinist by trade and when I say the squares were within .001", you can count on that being accurate. So I re-cut the parts that came out different sizes before, and they indeed cut about a millimeter different length over 8".

I removed the letter etching it had and moved stuff further apart and changed the power. Yeah, I know. I always screw up that isolating variables thing. Anyway, they cut similar this time. So I added some different letters to etch first and also added some reference lines to cut first, then scan the letters, then cut the shapes. This time the reference lines lined up and the parts cut correctly. I tried a few different power and speed settings on this same drawing and they all came out pretty close. Then I loaded the original problem drawing and it cut different again this time. I'm beginning to think it was a strange bug in RDWorks (note that the later cut tests were the same two parts drawing, just moved around the table). I installed Lightburn trial and gave it a short whirl. I'm gonna like it. It's late and I have to surrender for the night, but I'll try that again tomorrow. If Lightburn cuts that old drawing right, then maybe I can call it a software bug in RDWorks. I still think I need to tweak acceleration and speed limits since scanning occasionally misses steps (plus I'll get to know the machine limits as well). But maybe the machine doesn't have the problems I thought I had.

Anyways, I guess that's progress?
More later.

Oh, btw... Lightburn imported a DXF just fine that failed in RDWorks. Disco!

viewtopic.php?f=105&t=3528

Try this check - I too am a machist - close is never good enough for me.

Thanks Pete.
I noticed in my vendor settings that X and Y step per (x) values are close but not exact from the factory. First of all, that doesn't make sense. As long as things like belts are aligned well, the steps per (x) should be identical for a given pulley tooth count of course. The x & y pulleys are all the same in my machine, so the step per distance should be identical. So some tech at the factory did the cut & measure operation and entered values to get it close. My machine is indeed close, but of course nothing is perfect. My personal catch phrase at work is "perfect enough" (well, that, and also "It'll never work")

So my machine could use some tweaking for the step per (x) values for sure. Having built and set up some CNC stuff of my own, I also know that depending on pulley tooth count (diameter), steps per rev. on the motor, and microstepping value chosen in the driver, a guy ought to just be able to use simple math to determine the desired steps per distance in a machine.

Of course that by itself would not consider the kerf width. I dug around RDWorks and couldn't find any kerf compensation option anywhere. However, Lightburn DOES have a kerf compensation option in the layer parameters. Thus as long as it works, a guy ought to be able to enter the ideal steps per distance value into the appropriate axis values in vendor settings, also enter the correct value in the kerf compensation, and if all goes as you'd want, then you should cut accurate size parts with Lightburn. I want to look into this further and do some testing, but if I'm on the right track, then this is probably the way to go. You could also add backlash compensation and maybe even something else that I'm not thinking of, but seems like doing all this kind of stuff ought to churn out accurate parts reliably, barring mechanical problems or the like.

Kind of funny - this kind of setup is pretty well standard procedure for DIY mills & routers & the like, but so far I haven't seen any of the "apply some algebra" approach to setting up steps per distance for laser mechanical drives. This should also work just fine with and encoder/servo setup (with higher resolution of course).

Anyways, I'm kinda eager to dig in and analyze this a little when I get home tonight.

"the piece on the right cuts out about a millimeter longer"

That indicate an issue with the reverse interval

https://cartonus.com/how-to-improve-eng ... r-machine/

Look at this link for for guidance

That indicate an issue with the reverse interval

Sorry, I guess my post needed a TLDR.
Long story short, after testing, I strongly suspect a strange bug in RDWorks rather than mechanical problems or configuration tweaks (such as reverse interval). The problem showed up on a slow cutting operation after all, not scanning.

My tests the other night showed that some items would cut as accurate as expected reliably, but one imported drawing in particular had major dimensional error between two identical parts. Then I'd simply drag one of the two parts a few inches to one side and it would cut it accurately. Pretty goofy.

I had obligations last night which kept me away. But I'm gonna try Lightburn with similar tests tonight and see if results are different/better. That will at least tell me something.

Roger - let us know.