Burning through tubes FAST

Discussions on optics for laser cutter/engravers

Burning through tubes FAST

Postby scrappyjedi » Tue Oct 15, 2013 12:38 pm

I seem to be the black widow of laser tubes.

I purchased a used 2.x machine in May with a 40w tube with ~600 hours on it. I used it for maybe another 200 hours over the next 3 months and the tube failed. There was a gradual decline in power levels over the course of about the last two weeks of its use (during a heavy use period- probably more than 50 hours total), and then it got to the point where it wouldn't cut at all. Since the tube was a couple of years old and already had a bit a use, I expected it to fail at some point and promptly replaced it with another 40W tube ordered from LightObject (and I have to say that Marco was fabulous and got the tube shipped to me same day- on a weekend!). That was in August.

Now in October after ~250-300 hours of use, this new tube is experiencing the same type of failure. While cutting a large order this weekend the power started to drop off gradually, and it's showing the exact same symptoms as the previous tube.

I don't run the tube anywhere close to its maximum- most of what its been doing for those 250-300 hours is very light engraving, and the rest of the cutting has been done at around 8-9 mA. Yesterday I had to ramp that up to 12 mA just to get it to cut cleanly through 1/16" wood, and by the end of the day (~8 hours of cutting- my current order is all cutting and no engraving) even that wouldn't cut cleanly.

I suspect that cooling might be the culprit. I do have the coolant cycling whenever the system is on, whether the laser is actually activated or not, but it does run pretty continuously when I use it on nights and weekends. We had been using just a 5 gallon bucket of coolant, and after a cutting session it would be slightly warm to the touch, but not enough to make me think that things were overheating. Yesterday morning when I suspected a failure my husband went into action and hooked up a lab water bath/chiller to consistently feed 65F water to keep things cool, so if it's a heat issue I won't have that problem again. But even with the new cooling system in place, the current tube seems to be on the way out.

My question is- could there be some other cause of rapid tube failure? Or is a few hundred hours really all one can expect from a single tube? Could there be an issue with the power supply causing the failure? The new tube is on order, and I hope to have it in this week. I'd just like to keep it for a while longer than the last one!

Thanks so much!
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Re: Burning through tubes FAST

Postby jv4779 » Tue Oct 15, 2013 2:26 pm

On my 2.x I found that the cooling water had a huge effect on the cutting power of the laser, on the order of 1% decline per degree F the water increased. I didn't notice any cumulative effect and the "lost" power returned after the cooling water had cooled. Keeping the lens and mirrors clear also had a large effect on the cutting power. Even when the focus lens looked pretty clean, just hitting it with lens cleaner and a cotton swab made the cutting power go up.
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Re: Burning through tubes FAST

Postby scrappyjedi » Tue Oct 15, 2013 2:51 pm

Thanks so much for your response!

I also suspected the lens/mirrors yesterday, so we inspected and cleaned all of them in the evening and ran another test cut. Once again, it didn't cut cleanly through, even with power and speed settings that did work 2-3 weeks ago.

Yesterday I suspected that cooling might be the problem, which is why we installed the new water chiller. The tube now stays WELL under the listed operating temperature, even after 8 hours of cutting. With the new cooling system in place, though, by the end of the day yesterday it was still not cutting through boards (it started out in the morning cutting through well, though I did have to really up the power from the settings I had used just the week before to get it to do that). Cooling water was maintaining a steady 65F throughout the entire day yesterday, so there wasn't a temperature/power dropoff correlation. The power loss does seem to be cumulative over the last two weeks, and the symptoms are exactly in line with what happened last time my laser tube died.

Is there something about sustained used that kills the tubes? Or sustained use at a higher temperature? Prior to installing the chiller, the water would be 95F in the water jacket at the end of a long cutting day, and I would have 2 of those cutting days per week. We've fixed the cooling issue now, so if that was the culprit then the new tube should last a lot longer. I'm just trying to identify any other contributing factors before I install (and potentially burn out) yet another tube.
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Re: Burning through tubes FAST

Postby timogiles » Tue Oct 15, 2013 4:19 pm

I have also had problems with my output power dropping, and it was due to my cooling system. i started out with a DC-KIII laser with a small work area, so my longest jobs would last about 15 - 20 minutes. I built 2'x4' work area laser but kept my original cooling system (1 gallon bucket) and i found that my coolant would get quite warm by the end of a 3 hour job and towards the end of the job the laser wasn't cutting all the way through. I upgraded to a 5 gallon bucket and found that the laser power was much more consistent. Hopefully your new cooler does the trick.
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