[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.

[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.

[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

[Exsecratio]

100% subjective on your current ambient conditions.

As are most of the posts Dan it surprises me when people think they can change the laws of physics because they simply don't understand them

Robin, "Things", numbers are pretty much bang on the money I'll bet there will be somebody along soon who will argue with this

it is still a catalyst.

but then again they likely have never dropped Sodium metal into water let alone have the ability to understand Raman Spectrum analysis of CO2 as a gas

If you want to have your laser working stable for long time you MUST keep stable temp. 21-22C. No more, no less.

As it happens Cine, if you want your laser stable and for a long time you should run it at -28.88 Celsius but very few people have the materials or equipment to do that, anything else is a trade off of cost over effect.

As quite a few people will be aware, scientific analysis has no elements based on the validity of opinion, in fact science specifically places no weight at all to the opinion of the proposer and only theory that can be expressed in numbers or data values really carries any weight. Anything else is anecdotal at best

best wishes

Dave

[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.

[Rodney Gold]

The radiator/bucket/aquarium pump/fan is barely adequate for a 60 w, should be ok for a 40w basically the cw 3000 chillers are that or worse (some just water and a pump and a fan)
The CW5000 is a true chiller and will maintain temps of 20 or so on 80/100w tubes (Recis) , however it is generally $400 more than the cw3000.
Considering 40w tubes should be round $130 ex china , not sure a 5000 is a good investment. It is however , a good investment in a production environment for stable output power for the higher powered tubes.
Dont do the ice thing , we lost our first 60w tube cos of thermal shock of the cold water just after my operator added ice.
As to the beam shape thing , we get a donut with all our tubes and both our lasers (We are on our 3rd 60w tube and have tried all 3 of the 80w Recis I keep in stock ) BUT that is only on a very short low powered pulse when aligning (with cooling on) It worried me at first , however extending the pulse and power gave us the solid dot. All the lasers cut and engrave well , detail/line width/kerf is almost as good as my synrad and coherent based lasers.
We use ionised water in our chillers , and use a 50/50 mix with antifreeze.

[Robin Hewitt]

New tube and PSU arrived today, looks unbroken.

Don't think I want to solder wires to the tube, I'm thinking adhesive lined heat shrink to hold them in place followed by self fusing silicone tape?

I think the power supply is by K&N, the only instructions I get for the 6 wire interface are in the ebay listing. Nothing came with it. After reading the instructions a dozen or so times I think I have the idea...

Pin 1 driven low turns it OFF. Disconnected = ON
Pin 2 driven high turns it OFF. Disconnected = ON
Pin 3 driven low turns it ON. Disconnected = OFF
Pin 4 is GND
Pin 5 Volts sets the LASER ON/OFF duty cycle of an oscillator. Disconnected = FULL ON, PWM signal to Pin 1 or 2 sets the power.
Pin 6 is 5V out.

HQ Professional 40W Power Supply for CO2 Laser Engraving Cutting Machine 220/110 | eBay

Reassure me, please

[Exsecratio]

Hi Robin,

Soldering is fine but remember the electrodes are tungsten so won't solder properly, you also risk heat cracking the support. I use a dedicated clip that came fitted on my machine but I have seen others use "chocolate blok" type connectors very successfully. Just remember, not too much strain a good shield made from 4mm wall silicon hose is all you really need to insulate the terminal.

best wishes

Dave

[Robin Hewitt]

I really should stop searching the web

Some of these RTV silicones have a dielectric strength as low as 500 V/mm

Silicone tubing is good at around 7 kV/mm.

OTOH, a few layers of shrink wrap at 22 kV/mm is more than a bit tempting.

[Exsecratio]

Other thing to consider is where that power will go in the event of failure, it's not uncommon for tubes to arc to the machine chassis when the tube finally dies, too much insulation is going to make it track somewhere else. The 16mm x 4mm wall stuff I have on mine prevents running arcs but still allows arc though when the tube dies if I'm not standing by the machine. If overkill insulation means it's going to arc somewhere along the HT line(they are made by people that earn less a month than I do per hour) it's a case of hoping the path of least resistance isn't part of the operator

I'm no electrician, (Physics is my forte) but I know enough about it to know 35,000 volts no matter how many milliamps isn't going to end well if I'm in the way (and it bloody hurts)

best wishes

Dave

[Robin Hewitt]

No point asking for advice if you don't take it. 4mm wall silicone tubing is hard to find in short lengths, I did try. I can do it with two lengths of 2mm wall one inside the other.

One of my buddies is a Doctor of physics. I get to do all sorts things I probably shouldn't simply by getting him to countersign my application

[herby08]

Hi
I used a piece of shrink tubing and never hat a arc within the last three years and 3 tubes.
greetings
walt

[cinematic2]

For all those clods thinking they know everything better.

Synrads Instruction says:

The chiller`s temperature setpoint must be set above the dew point Temperature.
For example, if the ambient air temperature is 85F (29C) and the relative humidity is 60%, than the dew point is temperature is 70F (21C).
Adjust the chiller`s temperature setpoint to 72F (22C) to prevent condensation ...

Go back to school Mr. Things

[Exsecratio]

if the ambient air temperature is 85F (29C) and the relative humidity is 60%, than the dew point is temperature is 70F (21C).
Adjust the chiller`s temperature setpoint to 72F (22C) to prevent condensation

Read for content "Mr" Cinematic

if the ambient air temperature is 85F (29C) and the relative humidity is 60%, then the dew point is temperature is 70F (21C).
Adjust the chiller`s temperature setpoint to 72F (22C) to prevent condensation

Taking 2 variables and getting a conclusion that supposedly fits all possibles doesn't work.

IF the relative humidity isn't 60% then the dew point changes.

IF the ambient air temperature isn't 29C then the dew point changes.

Stick to something you are good at, as Maths and Physics clearly aren't two of them.

[Things]

Yep, even 30C at 30% humidity is well below 15C dew point. I don't see an issue, you need to figure this stuff out for yourself. I calculated that my laser will run fine without condensation at 15C in the winter months, whether that applies to you, I don't know, I don't know your climate. In the summer I struggle however, as even 23C water temp gives me condensation. For someone that says above or below 22-23C will damage the tube, I think a bit of schooling is required on your part, mate