Has this happened to anyone else?

Hi, I’m new to this forum. In fact this is my first post.
I bought a K40 a couple of months ago knowing it’s ‘issues’. I have read many articles on it. I’m a tinkerer and I have a background as a tech for industrial ultrasonic welding machines so I’m well aware of the dangers of high voltage.
Anyway, when I decided on the K40 I figured I was going to strip it down and fire the parts cannon at it. The wiring was substandard and much of it was just twisted together with un-shrinked shrink wrap on the mains. Well before long I had installed a DPS X7 controller, proper stepper drives, a higher quality LPS, an air assist laser head, proper industrial switches and an overkill axial exhaust system.
It ran beautiful for about 4 days then I noticed the laser power was diminishing. I had run some 3mm plexi with no trouble but when I tried the same program a few days later it couldn’t cut more than 1mm.
I checked the mirrors, they were clean. The alignment was spot on.
before long, a couple of hours, I had lost all power.
The LPS still worked and the milli-amp meter was reading correctly (about 15mA at full power) and the tube had a pleasant purplish glow when it fired. So I put a piece of paper in the path of the tube output and after holding the fire button for a couple of seconds it started to burn a rough ring in the paper.
Upon examining the tube I found that the back mirror (Hot end) appeared to be burnt.
I am using a five gallon bucket with distilled water and the pump that came with the unit. I always check for proper flow and for air bubbles before I start anything. I let the pump run for fifteen or twenty minutes to chase out any air.
I’m guessing there was an air bubble stuck in an area that I couldn’t see and that is what fried the mirror.
So has anything like this happened the anyone else?
I ordered a new proper 40W tube and it will be here in a couple of days. I have been spending my down time modifying the unit for the new tube since it is about six inches longer.
Like I said, I am a tinkerer and nothing makes me more happy than building and modifying but I did expect the tube would have lasted a couple of months.

Welcome to the forum Paul. Sorry to hear about your trouble. It’s always been theoretical that an air bubble could cause a hot spot, but this would be the first time I’ve seen it actually happen. :astonished:

I’ve seen sporadic mentions of occasional bad tubes that just burn out quickly even when treated right by people how know what they are doing, with speculation that the gas was contaminated. No first-hand knowledge though…

I’ve seen the reports of quick-death tubes too. Sadly, it seems that low-price tubes get sloppy manufacturing at times.
I think it’s interesting that the problem can be spotted at the hot mirror. That thing is under a lot of stress, as it works at a beam intensity of ~ twice the power exiting the tube. A little dirt, a poor polishing job, not enough water flow on the mirror, all of these things could overheat it quickly.
Still, all of my comments still reduce down to “bum tube”.

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Yeah, I’ve seen videos of some of the places in china making those cheap tubes. Down right scary.

Here’s one from the gplus days.