I have been using my Omtech laser and Lightburn for about 3 years now in a public school setting as a teacher. Today while running a project, the laser went crazy and our parts of letters in strange places, missed the outline of the project by over .25". Like it lost origin(zero) randomly throughout the job. and then just random scribbles. When I had this issue on our CNC, it was a corrupt post processor. My trust in just starting it again is quite low before I get it figured out and ruin another piece. Any ideas where to start here?
Please check the following and, if possible, send a screenshot of:
- Preview (Alt-P)
- Mechanical issues such as loose screws, insufficient tension on the belt
- layer settings (lead in, lead out)
- How many passes are you lasering? See the “E” in governor.
When I look into the crystal ball 
, I think it is a mechanical problem or a bad USB cable
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The first recommendation for a long-used machine is to delete all the files from the controller’s memory.
If the PC connects to the controller through a USB cable, go buy a known-good one with ferrite cores on each end. The ferrite may not do much, but it seems they command enough of a price premium to ensure better QC on the cable. Just do it.
Using a network connection is even better, although if that’s the case, ask the IT guys to verify the DHCP server isn’t handing out the laser’s (static) IP address to another device. That will cause baffling intermittent errors.
It is possible the machine has a mechanical problem, typically a loose setscrew in a shaft coupler, but the fact that the errors involve both axes moving at the same time suggests looking elsewhere. Just in case, this test pattern helps identify mechanical problems:
Scale it to fit the platform and run it as fast as it will go in Line mode with optimizations turned off and power set to mark a sheet of cardboard. Any differences from the design will be informative; a photo will let us look over your shoulder.
Also, always use something cheap like cardboard until you’re certain you’ve resolved the problem.
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In the distant past, I had similar problems sending files via USB. A change to TCP/IP via internal network solved the problem. Even if you don’t have a wired network, you can create one with an inexpensive router connected only to the PC and laser machine. You may also note an improvement in file transfer performance and machine response.
The preview looks good.
I did a fill pass and then followed it up with a line pass to sharpen the letters up. All the letters which are “normal” look really good that way.
I see several mentions of bad USB cable since you posted a response. I can certainly try that, as a quick and easy solution.
I have an endless supply of cheap cardboard sheets I can practice on. This is the first time I’ve had an issue with the laser since new. I will try everyones suggestions and run a test piece.
I don’t know which laser you have and whether this laser also has a connection for an USB stick… It would be a simple, quick and inexpensive way to save the G-code to the stick and then test whether it works better that way.
I may have got the craziness to go away, but now with the cheap cardboard sample piece, I see when running fill mode, it goes outside the lines to the left of all letters. I am running 13" per second, is that too fast for the laser to turn on and off? I wouldn’t think so, but I’m fairly new to the laser world. Sample is shown here. It appears to be perfect on the right side of the letters, but the left is off, both when burning left and right.
Yes, I think that’s way too fast… I guess 1,000 to 4,000 mm per minute… but that depends on your laser
If you search this forum for speed and power setting, you’ll find several recommendations.
The most common recommendation for diode lasers is to set it to millimeters per minute.
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What did you change?
It helps us to stay on track if we know what’s happening to the machine.
OMTech CO₂ lasers with a Ruida controller typically have top speeds of 500 mm/s, which is a bit over the 330 mm/s = 13 inch/s you mention, so that’s not likely a problem.
If you have not set the Scanning Offset Adjustment values, that will go a long way toward cleaning up the engravings:
A measuring magnifier will help get good numbers for the offsets, which you then divide by two for the table entries.
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I changed out the USB cord and reset the machine.
Thanks for the tips on speeds…I did change the units to mm and found that doing the sample rectangles mentioned above the sweet spot was about 250mm/sec. 200 was really good, 300 started showing sings of going past the outlined boundary. I’ve learned more about my machine in the past day than I knew the last 3 years. Thanks all.
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Given that the OEM USB cables came from the cheapest samples not immediately failing their QC, anything seems to be an improvement, particularly after a few years of plugging / unplugging / yanking / wiggling. 
OK, deploy a magnifier: you’ll see the improvement at higher speeds and lower speeds will look better, too.
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