Laser tube care and maintenance - newbie question

[Dranoweb]

Hello all,

I'm a newbie to the forum and to glass laser tubes, but not to CNC machines.

I have had a long read of many threads but have not found definitive answers.

I have just purchased, and am eagerly awaiting the arrival of a rather generic 40w Chinese laser engraver/cutter.

I'm firmly reassured by the ebay seller that it will cut vector mode, but this was only after I had to explain what vector mode was, so I expect to have to change a control board and do some mods.

This aside, as I have had no experience with glass laser tubes, I had considered the use of automotive radiator coolant (propylene glycol - suitable for aluminium radiators) as a replacement for demineralised (distilled) water. I currently and unaware of the exact configuration of the tube, other than the fact that it is water cooled.

I have read that these tubes typically have some kind of aluminium heat exchanged buried deep within the elegant coils of glass capillary tube, but know little more than my research tells me.

I have also read some indications that the beam (this is a CO@2 tube) will pass through the coolant at some point.

I'm interested to know if anyone can assist with some information about what is good and/or bad for a glass laser tube of this type. As it is my first, I would like to enjoy it's function for as long as possible before replacing the tube.

I am somewhat of an innovator and experimenter, and I am inclined to experiment, but I much prefer to do my research first, as letting the magic smoke out is not really an option right now.

In summary:

Is glycol based engine coolant good or bad?

Should I just stick with distilled water?

Are there any basics that one should know to obtain the best life out of a laser tube?

[zax15uk]

Hi Dranoweb, this will be obvious once the machine arrives and you look at the glass tube but it is infact a tube within a tube.

The center tube is the CO2 gas tube with mirrors at each end for the lasing and the outer tube is the coolant.

In addition it is common for the mirrors to be cooled with the same coolant supply, so yes the laser does pass through the water but only at the output mirror and for a short distance.

Now, as to what I would recommend for coolant. The best method would be an enclosed system using DI water with an optional clear anti-microbial additive, you could also use propylene glycol as the additive (most automotive products have added chemicals so I would not recommend those). It is important that the liquid be non-conductive for safety reasons.

So for a suggested cooling system, I would recommend a PC liquid cooler setup. Thermaltake make a good system, using their P-500 pump and 350cc reservoir. I think it's the Aquabay M5. Add a 120mm radiator and fan and you've got a complete system for cheap. It has a display for low coolant and temperature alarm, the only missing item is a flow switch. I have a Malema flow sensor and connected in series with the interlock wiring, so if the water flow is insufficient or temperature out of range it will disable the laser and save the tube from damage.

Now for the cheap method, also perfectly ok... a 2 gallon container of DI water with the submerged pump. If you add an aquarium water temp alarm you'll be able to monitor it and if you use a container within a container you can add ice to the outer one for additional cooling if needed. Change the water every 3 months as it will pick up impurities from the air, and if you are in a warm environment you'll probably need to add an algeacide. PC ICE Non-Conductive Coolant is an excellent additive, safe for the silicone tubing and non corrosive etc.

Zax.

[zax15uk]

One more thing, to get the maximum life from your tube - do not run it at 100% power. There isn't much increase from 90-100% anyway and it just causes premature loss of the cathode.

If you need to cut thicker materials, better to do it in 2-passes.

Zax.

[geekinesis]

I was wondering about using a pc liquid cooling system to save space. I wasnt sure if it could cope with the laser temperature? I normally use a 2 gallon water tank and have a temperature hovering around 25 degrees c. It rises to around 28 degrees c with moderate use of the laser at 20 percent power, and I use ice to cool the water using the two container method you described.
I would ideally like to get rid of the tanks and use a Thermaltake system if it was efficient enough?

[Dranoweb]

I think for the time being, I'll stick to distilled water with some algacide until I am a little more confident with the machine, as the manufacturer calls for distilled water only.

Knowing my history with new gadgets, I'd like to play this a little safe.

I had considered a PC water cooling system, and have decided on a variant instead.

I have a 20 litre bucket with seal-able lid, in which I will be installing a thermistor based relay controller and will interlink it into the kill switch of the laser unit. This will allow me to set the kill temp at my digression. The hope here is to limit the amount of debris and dust entering the system.

I will install a breather tube naturally (possibly with an air filter), and I intend to purchase either an automotive transmission oil radiator, or several "piggy-back" style PC cooling system radiators to cool the water as it returns to the bucket.

Until I decide on what type of heat exchanger to use, I have done a little math and have ascertained that I should have enough thermal capacity in the bucket (when filled with 15l) to suffice for short (calibration) runs until the rest of my gear arrives.

I have a digital temp gauge with a probe at the bottom to measure intake temp so that I can keep an eye on things until I set up the thermal cut out.

I also plan to have the intake (pump) low and outlet (from laser) high to capitalize on convection.

I Have also investigated a larger plastic garbage bin as a suitable outer container that should provide a nice ice gap for those longer runs. I have a theory that adding a reasonable amount of salt to the ice will melt it while retaining the low temp and will allow better heat transmission through the bucket, but if I have to go that far I'll be considering a chiller.

Just checked my postal tracking number today, to find that it has left customs in Melbourne this afternoon.

I should lay eyes on the real thing any day now.

[Dranoweb]

Originally Posted by zax15uk If you need to cut thicker materials, better to do it in 2-passes. Zax.

I have read this in other posts and texts that I have dragged up in the course of my research before purchasing this machine.

It appears to be sound advice.

As I am currently employed as a CAD operator, I often go to a local engineering company to have some of my designs cut with an industrial laser cutter.

The fellow there was extremely helpful in tips like this, however he did mention that life is likely to be much more difficult at 40w as opposed to his unit, which I believe is capable of something like 2.5 inch steel. Simply amazing piece of equipment anyway.

Been in love with it ever since I saw it.

[Dranoweb]

Good News, it has finally arrived.

The tube appears to be intact, so still good.

The transport carriage had a couple of broken runners, but nothing that a lathe and some patience cannot fix.

On short bursts, the optics appear to have remained aligned well.

I am now stuck with another question:

How does one get rid of the air lock in the tube?

[zax15uk]

The air should work it's way out, if you pulse the water (pinch off the outlet for a moment) it will help remove the pockets.

Where is the air trapped? Are you getting sufficient flow, both in the tube and to the mirrors.

Zax.

[Dranoweb]

The pump has not yet arrived, However I have a smaller equivalent that I am using simply to ensure that water will flow correctly.

I managed to remove all but one bubble with the pulsing method as suggested.

Tonight I plan to raise one side of the unit slightly while the water is flowing to try and dislodge the bubble by means of gravity (or floatation).

at the moment the bubble is trapped just above the primary mirror (opposite beam end of tube).

[Dranoweb]

Originally Posted by zax15uk Now, as to what I would recommend for coolant. The best method would be an enclosed system using DI water with an optional clear anti-microbial additive, you could also use propylene glycol as the additive (most automotive products have added chemicals so I would not recommend those). It is important that the liquid be non-conductive for safety reasons.

As far as anti-microbials go - what would you reccomend?
I notice that many are chlorine based, and off memory, that can be rather destructive to most metals.

I have observed that the water does indeed come into direct contact with the mirrors in the tube - and of course I do not wish to risk oxidising or eroding these in any way.

[fullspeceng]

I run 50/50 antifreeze/distilled water. You can buy it in the automotive department.

I really wouldn't worry about it. The replacement laser tubes are only like $200-300 and I haven't had a single problem yet over months of usage.

If you got one of the cheap Chinese lasers that does "NewlySeal" you will be very disappointed and not be able to do much with it. If you have one that does "NewlyDraw" or Moshisoft, you won't be able to do anything besides lightly engrave or cut paper. The DXF import is also somewhat broken.

Check out my website at: www.fullspectrumengineering.com/co2laser.html

I can sell you a Mach3 conversion kit if it's the same cables (>95% chance it it, all the lasers use the same cables to run Moshisoft and Newlydraw control boards).

I also sell a nice extruded aluminum water cooler + tank + pump that's way better than the aquarium pump with tubes that don't fit that you are likely going to receive.

Count on your laser tube being out of alignment when you receive it so spend some time aligning it and you will get 100x more power.

[Dranoweb]

Yes I had read that my options may be limited, but I purchased after researching my upgrade options.

I'll decide on what to do after I have had some time to experiment and learn.

My main interest in balsa wood and acrylic.

I did a few test firings last night, and the results were not thrilling, but I was not game to try any more than a few 1 second bursts without the correct water flow.

I have done quite a bit of homework and have found one guy who was able to get it to work in vector mode by selecting "outline" mode on the output selection.

But as I have yet to touch the software, I can't say for sure.

From the tracking number, I am expecting to see the software and other accesories this afternoon when I get home from work. I will post more then.