Engravings fail Above 15% power?

Hi everybody, so I’ve been have engraving issues for a while which doesn’t bother to much as just about everything I do consists of cutting operations only. My machine is a homemade co2 laser using a Arduino uno running grbl 1.1h, I dont beleive that lightburn or grbl is really the issue here.

The Problem:
When i try to engrave just about anything over 3in long the laser will just stop at some point then i need to unplug and re plug the usb to the Arduino to get a connection again. Making me thing its some kind of connection issue.

The Tricky Bit:
I Always just play with the speed setting thinking that was the problem however i just noticed yesterday after tirating up in power during an engraving that the machine will engrave just fine up to 15% power, but once i go up to 20 or higher it will again just stop at some random point during the engraving leaving the controller saying busy till i reestablish the connection.

My Theories:
After passing some point in power power I end up building to much static electricity that causes a connection failure. (Idk though cause it cuts just fine going up to 50% power)

The additional speed used during engraving in conjunction with power above 15% is causing some kind of interference. (for cuts im usually between 4-15mm/s at around 45-50% power as compared to 100mms when engraving)

My Question:
I’d just like to hear some theories as to why you might believe this is an issue or maybe even a fix.(like idk trying to ground the laser tube on an additional ground or something) keeping in mind that the machine works just fine for cutting and engraving at or under 15% power.

I know you said it’s a DIY laser, but did you design and build the PSU and how is it wired to the tube? How have you calibrated power control (10-100%vs tube current)?
What is the ground floor plan? (power in, ps for logic, ps for laser)?
What is the interface between the controller and computer/lightburn?

Thanks for the response i purchased a 50w tube and psu from omtech, and i think is wired correctly as it works, other than engraving. As far as calibration no i have not but i know that that 50% is about 2ma away from the tubes stated full power of 15ma through the use of a inline ammeter. Im unsure of what you mean by ground floor plan exactly but the laser psu as well as the 12v psu for the motors is all grounded through the wall via their 3 prong plug. I had the frame of the machine grounded at one point through the 12v psu but i never noticed any changes so i removed that grounding wire while working on the machine. the arduino gets power from the usb connection and the board is also grounded throught the 12v psu which allows the motors to work properly. And finaly interface is just a shielded usb cable.

So what do you think?

Well, I can’t claim to be knowledgeable about lasers, but I do know a bit about electronics. It seems significant that at higher power you don’t have a problem or at a power lower than a certain range. I’m also intrigued that you are within 2mA of max with a 50% power setting. Your PSU should probably be dialed back in this case, if, for no other reason than you’ll get better control of your laser and increase its life.

Back to your problem, however, when a USB connectedCNC controller stops suddenly, especially when there is there is a correlation to a power setting (or impulse), then this generally implies a noise problem with the USB port. This could be ground related, hence my questions, but could be EMI that may be mitigated by using USB cables with Ferrite chokes. You can buy the chokes separately (they clamp on) or get a good quality USB cable with built in ferrite chokes (gold plated connectors not a bad idea either).

Thanks for the input, i’ll definitely look into buying some of those ferrite chokes and see what happens, in the mean time i can fill orders so i’m in no rush. Its definitely and interesting problem.

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