Wimminz – celebrating skank ho's everywhere

That’s one of the things I like this blog, I’ll type something and sit back and think “Now *that* will generate several replies and at least 30 pm’s” and it gets sweet fuck all, and then I’ll make an aside or a throw away comment, and get inundated.

So.. I am not an expert….

CO2 lasers are invisible to the human eye, but, while air is transparent to the CO2 laser, almost nothing else that is visually clear to the human eye is… so glass / acrylic / water etc are all opaque to the CO2 laser… as for safety, white a 1 watt red/green/blue laser pointer is more than enough to almost instantly blind you if shone into your eye, as the lens in your eye focuses the beam on the light sensitive cells at the back of your eye that give you sight, take no comfort from the fact that the eyeball and the fluid in it is opaque to the CO2 laser beam, you get just as blind if the front of your eye gets cooked and cut.

This is an UNFOCUSED beam from a 50 watt CO2 laser aimed at bacon, it’s a 10 second clip, 2 seconds in the beam ignites, INSTANTLY generating copious quantities of superheated water vapour, 2 seconds later all the water vapour has been driven out, the meat is being turned to ash / charcoal, 1 second later the target area is glowing at several hundreds of degrees, approaching a thousand degrees C, and then the beam shuts off.

***FUCKING*** painful, even it it just hits your hand, and possibly crippling if there happens to be a nerve under the target area, if it hits your eye…

If your laser is less than 120/150 watts, chances are it is going to be a sealed tube, if you want to know the shelf life of that tube, take the rated operating hours and divide by some number between 1,000 and 2,000… yes, that’s right, a *top* of the range tube with 10,000 operating hours will have a shelf life of 5 years, bit like car warranties expressed as mileage and or age, doesn’t matter which comes up first, so even brand new unused old stock turns to crap same way as a cream cake goes off, and then it needs re-gassing, which in practice often means a service exchange tube.

Watts aren’t linear, if 50 watts can cut X mm thickness of a given material, 100 watts won’t cut 2X mm, in reality it will be about 75% of 2x at a reasonable speed and with a reasonable quality cut.

Watts aren’t equal either, watts consumed and generated by the tube itself, even if you actually believe that a cheap Chinese 40w job will generate the same overall beam POWER as say a German made 40w tube, not a bet I would care to make, as beam power is incredibly closely related to the quality and accuracy of the mirrors inside the tube, and the gas mixture inside the tube, and quality costs money, beam *power* and beam *quality* are two different things, if you can focus a high quality beam to an area half as wide and long, or a quarter of the area, as a low quality beam, then at 25% power the high quality tube is putting in as much energy per square mm of target per second as the low quality tube at 100% power.

There is a technical term the laser guys use for this, but basically unless you can get heat into something faster than that heat can escape via conduction/convection/radiation, the temperature will rise, get it to melting point or ignition point and the stuff will melt or ignite.

If you want to CUT, you need a gas assist, just like the oxy-acetylene torch, in that cases uses oxygen to CUT once the main flame has HEATED the metal to low white hot, no gas assist, no cut, just melt…. a magnifying glass on a hot summer day vs polysterene is the same deal, it will melt, but not cut.

Your CO2 laser will be powered by high voltage high frequency electricity, in FATAL quantities, running in the same fucking tube and millimetres away from WATER used to cool the tube, again, cheap Chinese glassware, hoses and clamps, vs higher quality German or other, and then there is the whole question of earthing the box and electronics… the laser beam will burn or blind you, the drive electronics will kill you, it happens, with regularity…. it’s not the kind of electrical shock that *might* kill you, or *could* kill you, it is the kind that will *probably* kill you or *almost certainly* kill you.

Maintenance is easy and cheap, make sure the tube is always drained if the ambient temps get near freezing, make sure everything is lubed and free from insects and dirt and contamination, clean the mirrors as often as required, eg every 1 to 4 weeks, that’s about it.

Running the laser is like running a printer or plotter, it’s the least of your fucking problems.

A 40 watt Epilog will vastly outperform a 100 watt chinese ebay special, not just in speed or accuracy, but in longevity and material maximum cut thicknesses… of course it is also vastly more expensive…. these are both extremes of the scale, avoid both and go for some middle ground.

In closing, in metal machining, you use feeds and speeds, and you can buy books of ready reckoner tables for these, if you are running a 4 flute 6mm diameter endmill at 2,000 RPM into aluminium the optimal chip load per tooth will give you your feeds and speeds, so for example if each flute could cut 0.05 mm of material off the work, 4 flutes x RPM gives you 0.05 x 4 x 2000 = 400 mm/min

Lasers work on power, usually as a percentage or total output, and speed, mm/min, but nobody will sell you tables of the ideal speed to cut 3mm acrylic on your laser, trial and error is your *only* option, and then note it down, irrespective of the claimed total tube power or claimed maximum speed, this will determine actual time for each job…. 10% power @ 100 mm/min is very very similar to 20% power @ 200 mm/min, and try and avoid more than 80% power for extended periods… so if it takes 75% power to cut at speed X, that’s your practical limit.

Before I forget, repeatable accuracy is another bitch, the laser head should be able to go all around the table and get back to a precise point with reasonable repeatable accuracy, this is probably of the order of 25% of the minimum size object that can be cut, so 0.25 mm repeatable accuracy will probably give you a 1.0 mm minimum circle / hole that can be cut…. and it won’t be a perfect circle.

You won’t get fantastic repeatable accuracy on a big machine, unless you blow big numbers with 5 or 6 zeroes behind at it.

That, I think, is about it.