This is probably better suited for #beyond-the-manual
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Believe I can move it but don’t like doing so unless you’re good with it.
Aluminium and copper reflect CO2 laser light very well. I don’t know if it is damaging though. I destroyed a laser diode with a reflection from a mild steel plate but they are very fragile compared to a CO2 laser.
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I’ve done aluminum at 100 speed and 100 power multi passes. Really trying to bake in some molybdenum to mark the metal. It worked. Metal marking was ok, but not black, faint. No perceivable damage or degradation in laser performance…
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As far as I can tell, chlorine is the easiest and quickly dangerous mistake to make. There are other concerning materials I’ve run across, but most of these, the debate isn’t whether the substance is dangerous, but in what quantity it is produced.
Basically all of the carbon materials we burn produce some amount of carbon monoxide and hydrogen cyanide. The HCN is 25 times more deadly than CO and at some concentrations can kill you in sixty seconds. But that’s the thing, both of them it’s the dose that makes the poison.
Polyurethane apparently produces HCN at a much higher rate than acrylic and wood when burned especially with low oxygen availability. But the question I haven’t figured out is whether the amount you normally burn during a laser cut is enough. But seems scary enough, I’m gonna wait until somebody measures it.
Chrome tanned leather can release chromium gas. Hexavalent chromium is particularly dangerous for you and the environment since it persists. Here again, the thing that isn’t clear is how much and how dangerous, but seems better to just avoid. The bummer is that this takes recycling leather goods off the table.
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This one surprised me a little.
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My understanding was that the beam is increasingly defocused, and hitting that far down (and then back up again slightly more diffused because of distance + the anisotropic metal scattering) is quite a distance and should be plenty defocused to not cause a problem.
But this appears to be from a GF staffer… so…
So what is that material. Sheet steel? Stainless? Aluminum?.. Is it really a problem.
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99.9% at least should go out the exhaust, so I don’t see why poisonous is a problem.
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Think of the squirrels? 
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I don’t like squirrels as they attack our fruit and veg so HCN is too good for them.
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Nothing shiny like chrome. I believe they had a note about it somewhere in either the user manual or something that they sent out at around that time.
My gut feeling is that a 4" fan, similar to the one the GF uses for venting (under the assumption of a properly sealing vent tube) will pull more than enough air to remove any HCN or other fumes. A quick average of the CFM ratings of three different 100mm computer case fans (which the one in the GF certainly isn’t based on the noise alone) comes to 39 CFM, which works out to a box 3.3’ (essentially a meter) per side. This also works out to be 2/3 of a cubic foot of air PER SECOND.
Using a rough internal volume of 18x20x9" the entire internal volume of the GF is getting 100% fresh air every 2.8 seconds (again assuming what I feel are conservative CFM ratings for computer case fans of approximately the same size).
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Tangential question:
Is there any difference (in human safety) in the smoke produced from lasing wood vs the smoke from a campfire? Same thing? Or if not, why and how…
I can think of one difference. With a camp fire, you usually have fresh air with occasional breaths of smoke. With a laser in a confined space you would have constant low level smoke inhalation that you willingly breath, so perhaps it could be more harmful
I havent run any cuts on Polyurethane yet but I have run about 90 minutes continuous engraves. My ventilation is buttoned up tight though, I don’t have any odors or vapors during projects, except what’s left lingering in the GF after a job.
You’ll know right away if you have an HCN leak though. The gas displaces oxygen so the first signs will be shortness of breath then dizziness/confusion.
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Taking a look now, That bottom sheet is fairly reflective! I can see the LEDs clearly in it, despite the anisotropic metal texture…
The goal on this site is safety of final product, but handling of the wood, avoidance of fumes//dust, etc, can be derived from this list.
Some information explaining the terms (like Sensitizer) on the bottom of the page.
Some, like YEW, are pretty straight forward, (DIRECT TOXIN), and Oleander goes even further since every aspect is Toxic.
http://www.wood-database.com/wood-articles/wood-allergies-and-toxicity/
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The heat conditions are a bit different. For example, many combustion byproducts are also combustible so burn in the context of oxygen and heat. Some more of those could stay uncombusted in a laser cutter because you’re actively cooling the area.
On the other hand you’re trying to transmit the 40W of heat to as finely focused spot as you can manage which directly vaporizes the material rather than oxidizing it to generate heat in a normal combustion chain reaction. So the initial fume composition may be different as well.
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I HATE this plant with a passion.
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Ugh
Stainless, it seems. Magnets love it. The owner manual is extremely explicit, as is support, about not letting the laser hit the base of the unit, so I choose to avoid the risk. Maybe I will do some testing with some paper on a backstop and see what power hits .3 above the bottom.
I went to ReStore and bought a LARGE floor tile for $0.25 for my backstop. The laser can’t get through it without a LOT of effort, if at all.