[kewlkiwi]

The laser tube in my XYZ-made laser has had an easy life...
It's basically a retirement hobby, so sometimes the laser doesn't get used for several days in a row.
The tube has lasted almost 3 years so I've been expecting it to 'let the magic smoke out' for some time now.:stickpoke

On the latest job, it almost finished cutting through some 3mm MDF pieces when the power level seemed to briefly increase (indicated by a lot more smoke and burn marks on the top) for about 50mm, then nothing....

The tube is still glowing violet, and if I leave the job overnight then on startup the first 100mm or so works as it should - but then power drops off and stops as above.

So my question is to anyone who has had a tube die: is this how it goes?
And if it's dead, why is the tube still glowing?

Thanks!

Bob

[kewlkiwi]

Hello Bob,
1.We are the professional manufacture of Laser/CNC Machine.
2.We have two kinds of laser tube(common one and long life one)

[snip lots of advertising stuff]

Any questions, please feel free to contact with us.

Ok, can you answer my question then?

I don't need another tube right now, already have two spares.

What I want to know is: Is the tube, currently in the machine, that is behaving as described.... dead?
Is the behavior described, typical for a tube on it's last legs
Thanks, Bob

p.s. There is a forum set up on this site for manufacturers to post about their products - please consider using it.
(And not every day with nothing new either, or posting the same info over and over again...:tired:

[zax15uk]

Bob,

In general the tube output will slowly decrease over time and evenually be unable to output. The normal cause on low power tubes is not depletion of the gas but rather wear of the electrodes, and contamination of the internal mirrors.

Failures can also be caused by permeation of air and/or moisture, or more catastrophic damage due to heat/physical fracture of the tube.

What could be happening in your case (although I haven't seen this before) is that the tube electrodes are worn or gas levels have changed so the PSU is struggling to create output.

It could also be a problem with the PSU, so unfortunately the only suggestion would be to replace the tube and see.

Zax.

[Dubliner]

Zax, are there, in your estimation better Chinese tubes than others - I had read favourable reports of RECI laser tubes?

[zax15uk]

Yes.

It is more difficult to say which are the best, or better ones as these vendors are typically buying from multiple sources.

I am not convinced that the more expensive Chinese versions are really worth the extra cost (except for the cosmetic improvements), they may be but I don't have data to support it at this time. If you want higher quality I would suggest checking the Taiwanese vendors, but again there are bad examples available too.

Air cooled RF excited metal tubes would be the way to go if you want long reliability and higher power output - but of course you pay up front for the expected life.

Zax.

[kewlkiwi]

In general the tube output will slowly decrease over time and eventually be unable to output. The normal cause on low power tubes is not depletion of the gas but rather wear of the electrodes, and contamination of the internal mirrors.

Well, it has been losing power, quite gradually really, for a while - and considering it's age I've had a fair go out of it eh!

...unfortunately the only suggestion would be to replace the tube and see.

Yeah, that's the conclusion I've come to as well! [sigh]
I basically asked in case the symptoms were caused by something else that someone may have seen before - and because it's a bit of a hassle changing the tube and then probably having to re-align it all...
'Was hoping it might NOT be dead I guess!

Ah well, better get stuck in and see if the spare tube still has any gas in it after all this time.

Thanks Zax.

[Magritte]

Can you tell us when you get the results of this bob?

I seem to have discovered a similar problem with my laser today.
Thanks
Henry

[Dubliner]

Kewlkiwi, you raise a few interesting points for me as I only have one tube with my machine, & it could last a year or an hour, & therefore having an extra tube on hand might be advantageous. The question is shelf life of "unused" tubes. As I've even heard of the tube warranty being based on the date of manufacture not the delivery of the machine ( which was the case with my machine. SO if it was on a really slow boat from China, the tube warranty might expire before you got your machine. There are a few re-sellers here in the US so it might be to my advantage to wait & get one when I need one. What are your thoughts on that?

[MonoNeuron]

From what I have read 3 years is EXTREMELY good for a glass Chinese tube. My 35 watt one only lasted 8 months and that was without use. I hope all your other tubes in storage are ok as the epoxy holding the ends on seems to outgas into the tube corrupting the gas quality or lets in the nasty impure outside gasses.
If the laser gained power it sounds like it would be a power supply problem more than anything else.

Check your connections to the tube or see if any wires have rubbed through onto the case causing a bit of arcing.

How do the wires connect to the Tube?
If it has the wires wrapped around them then unwrap and reconnect with good quality aligator clips or use earth BP screw connectors with 2 screw holes in them.

Just a stab in the dark for me but probably worth a look anyway.
Rich.

I was just thinking....If the tubes do indeed suck in a bit of outside gas/air then I might run a little bit of silicone sealant around where the ends are glued on and see if that makes any difference to the longevity of the tube. Probably hard to tell as they seem to all have different lifespans anyway.
just a thought but might be worth trying....

[kewlkiwi]

Changed the tube today, didn't need much to re-align it fortunately.
Started off the same job it was running yesterday...
The engraving part went ok.
The outline cut started off ok, and in fact did about ¾ of the circumference of the job... and I was rubbing my hands and thinking 'Great, I'm back in business!'

Then it the power level went UP (flame2) and started burning for about 80mm, then dropped right down to the point where it was barely making a mark - and finally, power dropped to zero (but tube was still glowing)

So whatever it is, it's not the tube - and I've wasted a day putting the new one in - but at least I now know: The old tube may still have some life in it, and the new tube still works after sitting in storage for ~ 3years.

I guess the next thing is to test the PSU, and I'm not sure how to go about doing that - other than getting another one 'on spec' and hoping that will fix the problem.

First off, I'll put an ammeter in line on the cathode end of the tube (negative line) and check the actual power when it fires initially and when it drops back.

The laser came with a huge wire-wound resistor and a sheet showing how to use that instead of the tube to test the PSU.

I've never tried it before because the instructions are far from clear (and the photo shows the meter's needle hard-up against the maximum pin-stop!) and, of course, I've not needed to up to now.

One thing to be tried first though, is checking the PSU isn't full of dust-bunnies, or my case - cat hair.
It does sound like it's the high voltage PSU though - just as well there are plenty of them on eBay etc.

[kewlkiwi]

... So if it was on a really slow boat from China, the tube warranty might expire before you got your machine. There are a few re-sellers here in the US so it might be to my advantage to wait & get one when I need one. What are your thoughts on that?

Based on how my first tube lasted so long (maybe it's something in the NZ air!) I think you are best advised NOT to have a spare.

(Well, at least until you think your current one is nearing the end of it's life, power dropping off etc and how old it is/how much work it's done)

Since there are, as you say - several re-sellers, that makes it fairly easy and quick to replace when it finally dies.

[kewlkiwi]

Can you tell us when you get the results of this bob?

I seem to have discovered a similar problem with my laser today.
Thanks
Henry

See above Henry - and good luck!

[kewlkiwi]

...
If the laser gained power it sounds like it would be a power supply problem more than anything else.

I'm coming around to the same conclusion. The fact that it starts off ok, at normal power, would seem to indicate the tube is ok and something else is the problem.

And then, just before it drops right away, the power seems to increase, because instead of just cutting cleanly through the MDF it starts to burn and the kerf gets wider before tapering away to nothing.
It all seems to point to the PSU.... Oh well, at least they are not as expensive as the tubes. (That's me, looking on the bright side!) :banana:

How do the wires connect to the Tube?
If it has the wires wrapped around them then unwrap and reconnect with good quality aligator clips or use earth BP screw connectors with 2 screw holes in them.

They have alligator clips. I did consider changing to the connectors (and in fact have a box of ceramic ones somewhere) but decided not to on the basis of 'If it ain't broke, don't fix it' - and also a small worry that if a somewhat violent event occurred to put stress on the wire/tube (like a Christchurch earthquake LOL) then the clip would probably just pull off, while a connector block might put enough tension on the short wire to either damage the tube, or the glass seal around the wire - or even break the wire off short.

I was just thinking....If the tubes do indeed suck in a bit of outside gas/air then I might run a little bit of silicone sealant around where the ends are glued on and see if that makes any difference to the longevity of the tube. Probably hard to tell as they seem to all have different lifespans anyway.
just a thought but might be worth trying....

Well, can't do any harm I guess!
Is the gas pressure inside at the 'normal' air level of 14psi? 'Wouldn't be higher I suppose, 'cause that might cause the end caps to blow out, but if it's lower than 1 atmosphere then the outside is is always trying to get in.

[Magritte]

Well mine seems to be firing plasma out the side of it now so I guess its the tube
I have a had that tube over a year but hardly used it so it must deteriate some degree by itself.

Do people buy thier tubes from vendors or ebay?
They seem to be cheaper on ebay even taking into acount duty and VAT.

[zax15uk]

The tube is under vacuum (typically around 30 torr) so yes the air outside is slowly (you hope) leaking in and contaminating the gas mix. It doesn't make much difference if the tube is used or not, the leak rate is fairly constant.

The permeation of the epoxy seal determines the shelf life, typically 6 months to 2 years. If done correctly the metal to metal seals for high end glass tubes should be hermetic. This comes at substantial added cost of course.

Ebay is fine for replacement tubes, just make sure the insurance covers breakage because they are fragile and need to be correctly packaged in a solid tube.

Zax.

[cdesigns]

I have a 40watt laser engraver with this chinnese tubes.

Water temperature is very important to have full laser output.

In my case I cut 1/4" wood for my projects and I have to mantain the water cooled to around 60F-75F to mantain full laser output power, if I forget to add ice to the water, the laser wont go thru the wood. if I let the water in the 85F range the laser tube loses power.

Always mantain a temperature probe inside the water tank, cooler or whatever you use, mine is always around 70F to 85F depending on what I'm doing. never let the laser work over 90F-95F for prolonged periods of time, mine reduces the power to about 65% and it doesnt cut the wood unless I lower the speed of cutting.

PS: also mantain the lens and mirrors clean, the reduce power when dirty, specially the last lens if its dirty "smoke residue" your laser cutting power will reduce a lot.

Hope that helps

Here is a video of my 40watt laser cutting the 1/4" plywood

[nomedia="http://www.youtube.com/watch?v=469B-V7a84o"]YouTube - laser[/nomedia]

[kewlkiwi]

Arrgh.. I had a long message all ready to post, and went back to edit the speeling errorors and also added a 'plus/minus' (ALT 0177) symbol to a number - and the whole lot was wiped & I got dumped off the board!

So long story short:
Problem solved, it was a crack in the lens - couldn't see it until the lens was taken right out and then it fell apart in 3 pieces.

It seems what was happening was this. On short cuts, no problem, air assist keeps the lens cool and - as the crack was off-center - it didn't affect the focused spot enough to notice. On a longer cut, enough heat was absorbed by the crack to make the lens expand in the holder (upwards I guess) and the focus changed so the beam became wider (bigger kerf) and it no longer cut right through the MDF (smoke could no longer escape underneath).

Stuck a new lens in, and away she goes.

Only dilemma now is, should I put the old tube back in? It may have another year of life in it, t'would be wasteful not to use that. :devious:

OTOH, it might die the day after... :violin:

[zax15uk]

I'm glad to hear you got it fixed, a cracked lens wouldn't have been on my short list for that kind of problem so good find.

I would leave the current tube in, you can keep the used one as a spare.

Zax.

[Dubliner]

I agree with Zax - I would have been searching for that one forever. Good for you & for us. These tubes are way more durable than everyone else has told me. I realize there is infant mortality, but at the cost of a tube, just figure out the dollars that "cheap" tube made you. This is how hobby CNC routers started off, made with window screen rollers & unistrut. Now look at them. I have a Shopbot & its bulletproof. Bully for you Kiwi.

[kewlkiwi]

Ok, I'm going to leave the 'new' tube in, mainly because I cant be bothered going through it all again :tired:

It was an interesting problem, and I'm glad it could be fixed without any delays of having to order and get a PSU.

'Still have to get a replacement lens of course, but in the meantime the laser is up and running. :cheers: Thanks Guys.:wave: