[Cathode]

My project log thread is started at http://www.cnczone.com/forums/showth...020#post301020

[jmg]

Rick,

I'm in central Ontario, about an hour drive north of Toronto.

I'd like to be able to cut steel, however, that requires RF laser, such as Synrad or Coherent metal tube types. From what I understand, glass tube Co2 can't cut metals (correct me if I'm wrong). Since I can't afford Synrad, glass tube is my direction. I would like to cut leather, and acrylic materials also, so glass it is

How about you, what materials are you going to cut/engrave?

I'm going to "bookmark" your thread to see how you make out with your build, I suspect it's going to be a good one! It looks like you've done a fair bit of homework already! BTW, I think you can raise your sights a bit higher...the thread you gave me logging your build identifies 1/40", you should be thinking (if you want to use fractions that is) along the lines of 1/400" or so.

take care,
jmg
P.s. you're quick on the reply!!...I haven't even checked Mach's manual yet!

[smartcut]

Hello !

Be fully advised of laser safety rules before any use ! Your IR goggles DO NOT protect yourself against a direct beam shot or a too powerfull specular beam.

You MUST use a proper screen so that the beam never escapes (3 mm steel is sufficient for your laser power) from any direction (reflexions). So see the process, you can use a polycarbonate screen if its damage threshold is greater than the most powerfull specular beam you might have (it depends of the target).

Take your time. Learn all that necessary about safety. After, it would be too late !

For information, the laser tube illuminates with a green/purple fluorescence (due to nitrogen gaz used to pump the CO2)

Enjoy !

[smartcut]

Disregard ...

[Cathode]

Thanks. I agree...safety is number one and will be one of the big challenges in this project. I will have a lid over the table with some polycarbonate windows. I am considering using cementboard and ceramic tile for termination, since I can work with those materials easier than steel.

[smartcut]

Hello !

I used to make some experiments on ceramic materials with my CO2 laser and I was amazed to see how quickly they can be damaged ! But well, it would be the same with a polycarbonate screen ... if the main beam is reaching it.

So it is very important to know the damage threshold of each screen material you are using to be sure not to exceed it in the worse case and during the longer on-duty time of your cutting machine.

I personnaly use my CO2 laser for material processing experiments. The beam never can escape. My experiment box (steel made) is covered by a 10 mm thick polycarbonate cover ... or ... with a full 3 mm thick steel plate for some experiments on very IR reflective materials !

I have no experience with cutting machines, but I guess that it must be very important to know exactly what material to cut and NOT to cut just to be sure that the reflected beams would not be too powerfull for the screens ! Probably some IR detectors must be used to cut off the laser power supply for example in case of mirrors misalignment ...

All the best.

[Laser.Tech]

Safety is, of course, the most important factor in any endeavor. HOWEVER, it is possible to get a little carried away...

A laser is just another tool, with it's own do's and don'ts, just like any other tool. Here are some points to consider, in no particular order...

1. An 5kw industrial cutting laser can slice thru 1 inch steel. But your NOT going to find one with a 1" thick steel enclosure. What you will find, is a 1/4" or 3/8" thick large polycarbonate window for watching the work...with a RUBBER bellows enclosing the raw beam delivery path...they would last about a tenth of a second if exposed to the raw beam...

2. You have to design for the worst case, but WHAT IS the worst case? If the mechanics are designed so that the mirrors cannot move or be moved out of the beam path, then the worst case is a mirror failure. This would result in a VERY hot mirror mount. Nothing else.

3. On trying to cut relflective materials: this would almost certainly be the worst case your going to encounter. Imagine having a severe judgement lapse and putting a laser mirror on the table to cut. What's going to happen? If your using a 2.5" focal length focus lens, and your enclosure is, say, 12" away from the table, then by the time the beam hits it is nearly 3" in diameter. At that power density, it's going to take quite a while to melt thru, assuming the beam is stationary the whole time. And this is the worst case. A sheet of polished aluminum wouldn't be nearly so bad. Now, that said, if you are using an un-focused beam, THEN you have a very dangerous situation...

4. Common IR detectors DO NOT WORK with CO2 lasers. This wavelength WILL NOT PASS thru common materials that will pass visible light. Glass, plastic, water, etc. are TOTALLY opaque to CO2s. This is why you don't need special laser glasses to protect yourself. I can't help but laugh everytime I hear someone spent a ton of money on laser glasses. A good pair of REGULAR safety glasses are perfectly acceptable. They will not allow ANY of the light thru, so don't worry about long term exposure...

5. It is required on commercial lasers that the protective covers be interlocked to shut off the beam if the cover is opened. Note: you do want the type that can be overidden, for setup and maintenance.

6. A common practice in laser environments is to interlock the laser with the doors to the area. That way, if someone unprotected enters, the laser is disabled. You can use ordinary door alarm switches...

7. It would be wise to have some type of motion feedback to shut off the beam if movement of the cutting head stops for more than a moment. Additionally, the beam output should be tied into the motion control hardware/software if possible (i.e. anything that stops movement stops the laser also), such as faults or E-stop.

8. Don't over-estimate what a laser can do. At these power levels, it's not going to burn thru any but the thinnest sheet metal. 1/8" aluminum plate with a rough or black surface, or light guage steel will make a perfectly adequate enclosure. The raw beam will get it hot, nothing more.

There is a lot more, but my point is that a laser is no worse than any power tool. If you take the right precautions, you shouldn't have any worries. My table saw and mill scare me a LOT more than a 5kw laser. Yes, there is always the chance that something you could never foresee could go wrong. But that is a risk with anything...

Brent

[smartcut]

I totally agree with you !

Your point of view is of course the right one.

But it is important to have the exact knowing (like yours) of the physical properties and limits of the "tools" used. Lasers ... or any other tools ...

The lack of knowledge is dangerous !

I personnaly use an oxy-acetylen cutting torch ... that I consider a much more dangerous tool that my 100 W CO2 laser !!

Many thanks for this detailled risk analysis.

So long !

[Laser.Tech]

Oxy-acetylen torch!? Now THATs dangerous!(flame2)

But it is important to have the exact knowing (like yours) of the physical properties and limits of the "tools" used. Lasers ... or any other tools ...

The lack of knowledge is dangerous

Now that says it all, really. Hope I didn't sound rude in my last post, I just see a lot of misconceptions and myths concerning lasers, and I wouldn't want to see anyone scared off from experimenting/working with one, or spend too much time and money, out of mis-placed paranoia.

The great thing about the internet, and this forum in particular, is 'lack of knowledge' can now be quickly cured...

Salut! :cheers:

Brent

[Cathode]

Thanks for all the great input, Laser-Tech and Smartcut. Not rude at all.

Lately, I’ve been getting a little too comfortable working around the laser. At first I would double and triple check each move, cause I really didn’t know what I was doing. But that got old fast. Just the other day I caught myself rushing to turn on the laser without turning on coolant flow. I did catch myself, but it could have been a meltdown. I think the moral of the story is to design safety in. But that doesn’t mean you can ever stop thinking about what you are doing, when working with a potentially dangerous tool.

Rational or not, there are three factors that make a CO2 laser slightly scarier to me than ordinary tools.

1. Lasers use high voltage and water. We’ve been told our whole lives that these two don’t mix. You can’t see high voltage. Once you reach the 10 KV range, insulation is only so effective. Once false move and you are a goner. Add leaking water to the equation and there’s a recipe for disaster. Add in Murphy’s Law and it is only a matter of time. I know from experience that Murphy’s Law will come into play at some point.
   
2. IR is invisible. We fear what we cannot see. You might not even know your beam is off target until you smell smoke or see an unusual glow somewhere in the lab.
   
3. I never designed a system that uses a laser before. We fear the unknown. I’m probably not even aware of all the failure modes that can occur. This is scary. So, again, thanks for all the input. I wouldn't attempt such a bold design without this fourm for support.

But, at this point, all this is good. These fears won’t stop me from experimenting, but will force me to be a little extra cautious.

I really like the motion detector idea, to shut off the laser if it stays in one place for too long. If anyone has a component to do this, please share. I’m thinking, something from an alarm system could probably be used to implement this function. I’ve already got the low flow shut off and interlock switches for my machine. I’m am still bench testing, so nothing is in place yet.

I hope to post the result of my power measurements and other experiments soon. They will be in my project blog. My day job has been keeping me pretty busy. Plus, we just added on a room to my house and are in the process of remodeling. I keep telling my fiancé that the laser cutter will come in handy for the finish work. Right. I’m hoping to get to use by this fall to cut some nice veneer inlays. That day will be a milestone.

[Laser.Tech]

Rick, glad things are coming along (and you still have your eyes)!

Heres a good tip you may already know...while setting up the laser, ALWAYS use a MANUAL MOMENTARY SWITCH too fire the beam. Think deadman switch. Use short 'bursts' to verify where your hitting. If you need more hands, ask for help, but never leave the beam on by itself. I've had a couple incidents where that momentary pushbutton averted a BAD outcome. And one VERY SCARY incident where a sustained beam was involved (still shudders!!).

HV + H2O always calls for awareness and caution, in any application.

Don't really know how motion sensing is normally done, just the idea. If I come across anything I'll post it in your build log!

Looking forward to future progress,
Brent

[smartcut]

... and so I wish you a great success with your project.

Just some more informations : you should perhaps have a special TTL input (on a TTL connector) on your power supply you can use to prevent any use of the laser without water cooling.

For my own laser, I prefered to buid a main control box (with a key-switch and an emergency switch) that controls both cooling water pump and power supply. So no chance to forget to switch on the pump !

To prevent any electrical "disaster", you must ground all metal part that can be in contact with you and the high voltage source (normally, only one hot point). No water connection (just the input and ouput on the laser tube of course) inside the working area. The cooling system (pump, heat exchanger if any ...) must be outside.

A last thing : when you switch on the water cooling, just give time to the pump to throw off air bubbles before to work with the laser.

And to finish, not to forget something : you can make check-lists like for airplanes ! It is simple and it works.

All the best.

Philippe