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« on: July 05, 2009, 05:58:16 AM »
1/ I do not use a laser system at home, yet. I have used many laser systems.
2/ diode lasers "seem" like a cool idea, until you realise the drawbacks...
3/ diode laser like soft start and soft stop or they die very fast, CO2 lasers can go on/off at 10kHz or more no problemo
4/ diode lasers need low voltage and high current, CO2 lasers need high voltage and low current, lot cheaper...
5/ diode lasers above milliwatts aren't spot / single small round beam type diodes any more, they are usually bar / wide flat beam type diodes, suddenly the whole optics thing gets far more complex.
6/ diode lasers generally don't produce pukka IR which is what you really need to cut and engrave, diode lasers are FANTASTIC for use in creating light shows.
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I've seen with my own eyes 18 watt CO2 lasers vastly outperform 50 watt diode fibre lasers on wood / plastics / leather marking and cutting, not just in quality, not just in speed, but also in ease of use... but then the fibre laser was bought to engrave part numbers and branding on to small precision metal parts, and that job it did EXTREMELY well.
Tweakie has in reality gone about as far as you can with the low power laser diodes, rip apart an old CD or DVD burner if you want to play on the cheap, but it will tell you nothing useful about high power laser diodes or high power CO2 lasers.
CO2 lasers are basically just a glass tube with an anode at one end and a cathode at the other, and a mixture of gases inside which are excited by the high voltage (15-25 kV) much like a neon tube or flourescent tube... they really are as non complex as that.
the big difference between a neon tube and a laser tube is the mirrors and lenses, interestingly made of semiconductors for IR wavelengths, plus the tube is die straight, plus it may have an outer sheath that is water cooled.
the CO2 laser PSU is not just a neon transformer HT source, you can connect a potentiometer up to it, or a CNC machine output, and get on/off and PWM control of power, so your XY machine moves at a constant mm/sec and the laser simply goes on/off and various power levels to get the desired effect...
unlike the diode laser the tube CO2 laser can do this on/off PWM thing at many kilohertz with no ill effects.
to CUT as opposed to ENGRAVE you need (should have with engrave too really) a combined focus lens and air jet, so the vapourised material is blown away, you need to match feed rates / laser power / PWM duty cycle well to cut or engrave cleanly, with a CO2 laser PSU capable of multi-kilohertz response this is a piece of piss, 50mm/min @ 50% PWM gives the same delivered power per mm2 of work as 100mm/min @ 100% PWM, but on a given wood each may well burn to a different colour, hello "grayscale" - don't even dream about doing this with a diode / fibre laser.
Fixed laser tube and flying optics adds hugely to the build cost, those optics have to be spot on at both ends of the table X and Y travel, then more complication for Z focus... if you can mount the tube on the Z things get vastly simpler and cheaper.
health and safety and other legal stuff also adds vastly to the cost, HEPA air filters and sealed negative pressure cabinets and so on and so forth all start costing lots of money very quickly indeed... in my shed I don't need any of that stuff, I have a brain, and I'm not selling it as a turnkey commercial product.
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in science fiction the defence against a laser is a mirror, and basically it is right, anything that is "shiny" to THE FREQUENCY AT WHICH THE LASER DELIVERS THE BULK OF ITS POWER will not cut or mark at all well, an IR CO2 laser works best all round because not many things are "shiny" to IR, far more stuff is "shiny" to visible light..
Tweakies lower power diode laser will simply bounce off a glass mirror, but turn it the other way round and it will slowly burn through the silver coating on the rear of the mirror, then paint it black and you have a nice fancy mirror.
As anyone with a greenhouse or who drives knows, UV goes through glass and IR doesn't, so it is a LOT easier to engrave glass with an IR CO2 laser than with a visible light laser, the visible light laser will usually melt and crack the glass before it engraves, the CO2 will engrave on a mere fraction of the power the diode laser uses, and the flipside of power is feed speed, if a is 100 times as effective as b then a uses 100 times the feed speed.
A 50 watt diode / fibre laser is absolutely great if all you ever want to do is mark / etch metal all day long, it is basically ********* all use for cutting out material into patterns, cutting gaskets, engraving glass, or anything else.
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In closing
cheap CO2 laser tubes have a bad rep for "short life", eg 1,500 hours or so, you get a LOT more hours running it from a pukka DC laser power source than you do from a neon sign transformer, which costs nearly as much anyway, plus, 1,500 hours is 30 hours a week for a year, if you use it 5 hours a week it is six years, and don't forget diode laser life is not that much longer, and literally and absolutely killed the instant you use anything other than an ideal power source, it's like being given a random light bulb, the difference between "bright" and "blown" is fractional, but a tungsten filament light bulb is about a thousand times more forgiving than a laser diode... you could get (all other things being equal) 750/800 mW out of a bog standard DVD writer diode for several hours, maybe tens of hours, and save 455 bucks over that ebay thing, which is TOTALLY lacking in all the essential info (looks like a surplus Coherent unit though)
but tubes are fairly cheap and easy to swap out, just like changing a flourescent tube in many respects.
CO2 lasers are also very well understood, which means it is easy and cheap to take adequate safety precautions, unlike diode / fibre lasers you can actually watch a CO2 laser below about 50 watts work via a sheet of thick glass / acrylic and safety goggles
CO2 lasers are mass produced, and the only game in town when it comes to producing a genuine beam at any decent levels of power, with no extra peripherals required.
CO2 lasers have essentially infinitely adjustable power output, diode lasers do not, more like an arc lamp, and CO2 lasers can be turned on and off in 1 thousandth of a second, diode lasers can not, you're talking multiples of tenths of a second to ramp up and down.
HTH etc
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