[Robin Hewitt]

Oops!

I forgot to turn on the water, the ring on the exit mirror detatched and I get a few seconds from cold before the mirror overheats and the beam starts to wander

40W 70cm tubes are not expensive but it is trying to work, China is on Spring break and this tube is aligned to the optical path. I feel inclined to try and fix it.

I see two options, either superglue or thermal transfer compound followed by a bandage coated in epoxy resin?

I will now go and hardwire the pump so I don't have to remember to turn it on :nono:

[herby08]

hey robin
just forgett it many allready try this it does not work at all, because if the chamber with the mirror-lense is seperated the most of the O2 gas is lost too.
save you the agrevation
greetings
walt

Oops!

I forgot to turn on the water, the ring on the exit mirror detatched and I get a few seconds from cold before the mirror overheats and the beam starts to wander

40W 70cm tubes are not expensive but it is trying to work, China is on Spring break and this tube is aligned to the optical path. I feel inclined to try and fix it.

I see two options, either superglue or thermal transfer compound followed by a bandage coated in epoxy resin?

I will now go and hardwire the pump so I don't have to remember to turn it on :nono:

[Robin Hewitt]

just forgett it

Hi Walt

You are probably right, but I have little to lose by trying

The mirror seal appears okay. It had overnight to leak and degrade but fired up strongly this morning so I may get away with it.

I had an idea and searched ebay for thermal adhesive and it does exist, I just bought some.

best

Robin

[herby08]

hi robin
yes you are right you have nothing to loos if you got the time to play with.
to glue this on you can take just crazy glue.
what you will experience is that you need to re aligne the beam a few times
greetings
waltfl

Hi Walt

You are probably right, but I have little to lose by trying

The mirror seal appears okay. It had overnight to leak and degrade but fired up strongly this morning so I may get away with it.

I had an idea and searched ebay for thermal adhesive and it does exist, I just bought some.

best

Robin

[Robin Hewitt]

what you will experience is that you need to re aligne the beam a few times

Hi Walt

I'm now waiting for the glue to solidify. I managed to fix it in place without disturbing the 90 degree mirror or removing the tube, using a humble wooden ruler and a couple of elastic bands

When the unused glue goes hard I will find out.

best

Robin

[Things]

If only the water cooling ring came off the mirror, you should be good to just carefully glue it back on. However, if the mirror seal to the tube was compromised in any way, it'll probably start leaking in air and eventually the tube won't do anything. Give it a shot anyway, nothing to lose.

[Robin Hewitt]

Well, it seems Walt was 100% correct. When my laser isn't arcing fit to burst it can barely cut through a piece of masking tape. I think the mirror has leaked air just like he said.

It's also making an unusual noise so I ordered a new PSU to go with the new tube.

They can't ship until everyone in China has sobered up and drifted back in to work on the 18th, so I think I might lose the Moshi part and drag this thing into the 21st Century while I am waiting

[cinematic2]

If "the mirror has leaked" there wouldn`t be lasering at all.
Null. Zero. Nothing.
You must have oveheated your laser so now it works bad.
Hope you didn`t glue output window :-)
Regards

[Robin Hewitt]

You must have oveheated your laser so now it works bad.

The tube and PSU are going in the bin

I have now gone paranoid about tube temperature, totally anal.

Question: I plan to add a thermal laser shut off switch shortly after the tube outlet. I can switch at 60 or 70degC (140 - 160degF). Which would you use?

I've also ordered a radiator, a fan and a panel themometer.

I dug out a flow meter from my junk pile, then decided it would be much easier to make a little pot with a hole in the bottom. If full it pushes down on a microswitch and gives the laser an okay to cut. I can 3D print it and make it integral with the hose clamps.

[Exsecratio]

The tube and PSU are going in the bin

Question: I plan to add a thermal laser shut off switch shortly after the tube outlet. I can switch at 60 or 70degC (140 - 160degF). Which would you use?

I'd go a LOT lower, by the time a sensor picks up 70 degrees it's going to be too late I very much suspect. Thermal overload tends to go in apparent exponential progression in most materials, to get it to 70 from 60 takes a lot less time than from 50 to 60.

Temperature doesn't start at 0 Celsius an old favourite at Uni was to bet a beer on what temperature is double 25 centigrade then take the money when they say 50

best wishes

Dave

[Robin Hewitt]

Thermal overload tends to go in apparent exponential progression in most materials, to get it to 70 from 60 takes a lot less time than from 50 to 60.

Hi Dave

I usually avoid doing sums on American sites. They usually go by the, "if more is good then too much is about right" philosophy. Strangely enough it seems to work, I drive the stepper motors on my milling machine at 220V and it is freakin' amazing

But if you are okay with words like exponential, let me ramble for a bit and try to get this straight in my head...

At top whack the tube takes 18mA at 15kV which is 270W

It puts out 40W (maybe) leaving 230W that need to go somewhere else.

That's 54 calories per second which will heat 1 litre of coolant by 1degC in 18.5 seconds.

As the water temperature rises the radiators ability to dump heat increases, but the waters ability to remove heat from the tube decreases.

Air is not very good at cooling anything, so I can see where your exponential rise in temperature is coming from. It's the flow rate past the hot mirror at the beam exit.

I think I need to impose a duty cycle on it, so rather than have over temperature killing the PSU and losing the part, I need the processor to look at the sensor and decide when to start the next cut. That way the radiator gets time to catch up.

I can either read the temperature and decide, or fit a disk thermal switch, say 40degC and use it's hysteresis to impose the duty cycle automatically.

Back to the drawing board

best

Robin

[cinematic2]

I have now gone paranoid about tube temperature, totally anal.
Question: I plan to add a thermal laser shut off switch shortly after the tube outlet. I can switch at 60 or 70degC (140 - 160degF). Which would you use?
I've also ordered a radiator, a fan and a panel themometer.
I dug out a flow meter from my junk pile, then decided it would be much easier to make a little pot with a hole in the bottom. If full it pushes down on a microswitch and gives the laser an okay to cut. I can 3D print it and make it integral with the hose clamps.

Stop that all.
Stay proffessional and buy water chiller like CW3000.
It has special electrical connection to PSU that will protect your laser against oveheating, lack of water and lack of water flow.

[herby08]

Hi robin
one more sugestion to connect your new tube this is from a big laser tube manufacturer.
you should against the way how the most machines come where the water connection goes in at the positive side and exit at the negative side , thats wrong it should be the other way around and the tube should be a bit slanted towards the exit side by just turning the tube a bit.
the reason for this is that the most heat is generated at the beam exit side of the tube and there should the cooled water enter the tube. the slant is that any airbubbles what are the same way dangerous for the tube are forced out.
the best water temperature is between 19 to 20 degreeC I am driving my tube this waywith a thermostat which switches the cooling fan who is in front of a 120mm radiator which is in front of a window airconditioner unit what I have anyway because it gets pretty hot here.
greetings
waltfl

The tube and PSU are going in the bin

I have now gone paranoid about tube temperature, totally anal.

Question: I plan to add a thermal laser shut off switch shortly after the tube outlet. I can switch at 60 or 70degC (140 - 160degF). Which would you use?

I've also ordered a radiator, a fan and a panel themometer.

I dug out a flow meter from my junk pile, then decided it would be much easier to make a little pot with a hole in the bottom. If full it pushes down on a microswitch and gives the laser an okay to cut. I can 3D print it and make it integral with the hose clamps.

[Robin Hewitt]

one more sugestion to connect your new tube this is from a big laser tube manufacturer.

Hi Walt

Coolant in hot end first, keep as close to room temperature as possble :cheers:

A 120mm radiator and fan is enough? I don't have air conditioning, hot weather is rarely a problem here.

This 50% laser power loss at 40C sounds tricky for a consistant cut, but at least I now know what to expect. Are there any other newby surprises waiting to catch me out?

I notice people are motorising their table height. I am assuming a manual adjustment to get the focus is enough if I only cut sheet, but my assumptions about lasers have not been very good. 60C became 40C and now it is 20C

Robin

[SPC-laser]

Well, it seems Walt was 100% correct. When my laser isn't arcing fit to burst it can barely cut through a piece of masking tape. I think the mirror has leaked air just like he said.

It's also making an unusual noise so I ordered a new PSU to go with the new tube.

They can't ship until everyone in China has sobered up and drifted back in to work on the 18th, so I think I might lose the Moshi part and drag this thing into the 21st Century while I am waiting

hey nice to meet you,and find you are looking for the laser tube,i am working now,and can DHL to you today.
best regards

Susu email:[email protected]
msn: [email protected]
SKYPE: cyosusu

[Things]

The mirror melting off the end is simply the adhesive giving way. As for the laser losing power as it gets hotter, it's because the CO2 gas in a sealed CO2 laser actually breaks up into it's constituents as you ionize it. That's why you have the large outer gas jacket, and usually a spiral tube inside the laser, it's to give the gasses time to recombine (With a catalyst) back into CO2, before going back into the laser bore again. As the laser heats up, the gasses break up faster than they would at normal operating temperature, thus lowing the effective gain of the laser.

If you were to actually burn something briefly with the unfocused beam, and ramped up the temperature of the tube, you'll actually find it jumping between transverse modes in response, giving you odd beam shapes: Transverse mode - Wikipedia, the free encyclopedia

I've done this on purpose once before, just because lasers in general is one of my hobbies, "mode hopping" as it's called is nothing new to me, however it's interesting seeing the effects of it actually burnt into a medium, vs just observing the dot on a wall for a visible laser:



I've found generally, they start losing efficiency above around 30C, although in reality I prefer to run them at around 15C. I'd set your temp cutoff for no more than 40C, and make sure your water loop is NOT completely sealed. As the water heats up, pressure will build up in a sealed loop, and most likely the first thing to pop off will be a water barb.

Of course, the mirrors going out of alignment is the other reason as you've specified, and is a sure fire way to lose power in any laser

[cinematic2]

1.Because of specific construction all chinese (glass) lasers works in TEM00 mode.
If the output shape is different than round this is not other transverse mode.
This is damage .
2. Typical chinese lasers DO NOT use catalyst.
Recombining is natural process.
3. 15C degree is to low.
It is to close to water condensation edge in specific situation.
4. 40C degree is to high.
At 40C laser will lose about 40-50% power.
Best temperature for chinese lasers is 21-22C.
If you want to have your laser working stable for long time you MUST keep stable temp. 21-22C. No more, no less.
If you want your laser engraving stable quality you MUST keep 21-22C.
So this is why people use proffesional coolers.

[Things]

1.Because of specific construction all chinese (glass) lasers works in TEM00 mode.
If the output shape is different than round this is not other transverse mode.

Yes it is. Damage doesn't affect the beam shape unless it's damage to the optics themselves, it's the lasing medium (In this case CO2 gas) reacting to varying gain. This is common in basically every type of laser, diode, DPSS, gas. The laser I produced the burn mark with above worked perfectly fine after being cooled back down to a good operating temperature (Confirmed with a power meter)

2. Typical chinese lasers DO NOT use catalyst.

Yes they do, typically H2 or H20. They fundamentally can not work without one. And yes, even though it's just water, it is still a catalyst.

3. 15C degree is to low.
It is to close to water condensation edge in specific situation.

100% subjective on your current ambient conditions. Saying 15C is oging to be a condensation issue is like me saying your car is too slow. It might be too slow on a highway road, but on a bumpy, rocky road, then it'll be fine. In some places condensation will even form at 28C. It CAN be a condensation risk, but if not, it's fine.

4. 40C degree is to high.
At 40C laser will lose about 40-50% power.
Best temperature for chinese lasers is 21-22C.
If you want to have your laser working stable for long time you MUST keep stable temp. 21-22C. No more, no less.
If you want your laser engraving stable quality you MUST keep 21-22C.
So this is why people use proffesional coolers.

He was referring to a thermal cutoff, not the recommended operating temperatures. If he wanted it to cut off when the laser started losing efficiency, then you're correct, but you aren't going to cause any damage at 40C.

[Robin Hewitt]

I've found generally, they start losing efficiency above around 30C, although in reality I prefer to run them at around 15C. I'd set your temp cutoff for no more than 40C

This sounds like quality information. I will plumb it in and see what kind of duty cycle I can get without straying above 40C

Susu, thank you for your kind offer, my tube and PSU have already reached the airport. However, I got the 40W as an introduction to laser cutting and expect to destroy a tube or two while I sort out the software. if I decide I like lasers it will not be long before I want a bigger one.

[Things]

I use a 1/10HP aquarium chiller I found at a recycle shop for $40 to cool my laser, works great for a 40W tube. Don't have to spend big money for a good setup, just keep your eye out for things that may be useful. I have seen people even put a bucket of water in a minifridge and just pump that through.

Technically speaking fridges have quite a small thermal handling capacity, so don't expect to be able to run the laser constantly and hold a stable temp, but if you use a large enough reservoir you can run for a good time before having to let it cool down again. Alternatively just use a bucket of water and add ice occasionally. The laser really isn't worried if it's operating at low temperatures like that, it's the higher temps they don't like.

Condensation on the tube I've found isn't a huge issue. A CO2 laser actually has "negative" resistance (will try to pull as much power as it can) once it's ignited, so it's a much easier path for the electricity than trying to track along the tube for the nearest ground. Arcovers can still happen though, I've had arcs jumping a good 2cm off the front of the laser to an optic mount when the ground lead slipped off the other end of the tube.

I run at 15C, because I live in the tropics, and anything much below that, the chiller just runs flat out trying to hold lower temps, so 15C I found to be a good spot where the chiller gets a few breaks, and the laser is still happy. The temperature they can cool down to is dependent on your ambient temperature too. So while the ambient temp in the garage might be 35C, the chiller can probably only get down to 10C or so reliably. However if I dropped the temp in my garage to 10C, it'd run along at 2C happily.

I'd agree that 21-22C is a fine operating temp for the laser, but saying anything more or less is going to adversely affect it isn't true.