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Messages - GuyFawkes

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1
Share Your GCode / Re: CNC Vacuum table project
« on: July 14, 2009, 05:32:03 PM »
Yes, use an edwards type vacuum pump, not a vacuum cleaner.

just use some neoprene rubber to cover all the holes in the vacuum table not covered by the part

holding force = no of holes covered by part (area) x vacuum

vaccum pump, even knackered one, will pull 13/14 psi vacuum easy, shop vac may pull 5, and will then overheat because the use the airflow to cool the motor usually

HTH etc

2
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.

================

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.

-----------------------------

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.

---------------------------------

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


3

Here is the unit I’m looking at: 
http://cgi.ebay.com/High-Power-Laser-Module-1000-mw-Cutting-Burning_W0QQitemZ180347420212QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item29fd8b3e34&_trksid=p4634.c0.m14.l1262&_trkparms=%7C293%3A1%7C294%3A30



are you insane?
445 bucks for 1 watt and no PSU

you could just about put together a 25 watt co2 system for that money, and actually have full power control over the laser output via cnc / pwm

if you want to cut you need a lens / gas jet assembly, end of story, without it you're just melting your way through. and yes you need a cutting bed, always...

4
sorry, don't understand what you're trying to ask/say.

5
Works in progress / Re: new italian touch screen
« on: July 02, 2009, 06:23:01 AM »
An English version would be excellent. TIA.

6
Apropos of nothing, the latest price list landed in my inbox this am, Chinese stuff in US$...

25 watt CO2 laser tube $127 or 40W for $158
pukka DC PSU for above $172
ZnSe or GaAs lenses various lengths etc $30 to $45
Cu mirror $16 quartz / silicon / molybdenum too

So you're looking at 400 bucks for something that will actually cut and etch etc, vastly versatile with PWM or potentiometer control on the laser, and if you bolt it to the Z axis that takes care of movement too.

Now I'm going to ask you, how much are you spending on "experiments"?

I know I wasted 12 months and maybe 20% of the cost of my CNC conversion by being cautious instead of being bold, determining what was needed, and going out and doing it.


7
Basically the above means that even the reflected and diffused beam from a 100mW laser is sufficient to cause irreparable, permanent, eye damage in less than 0.2 seconds.

Do not forget that at visible wavelengths, where the eye lens can focus the beam, a coherent beam entering the eye is focused to a point 100,000 times more powerful at the retina.

I know a man who has a permanent black spot covering about 25% of his field of vision in one eye, he described hearing a sort of "pop" inside his head as the beam caused boiling and cavitation inside his eye.

It was a 250mW "green" laser that did it.

Amongst other things he lost his truck drivers licence over it, one eyed jacks need not apply for a truck licence in the UK.

=====================

I have another mate who *KNOWS* lasers, he has a home built 80 watt CO2 laser, home built as he built everything, even the tube.

he dons a high end pair of very specific to the wavelength goggles, and then a modified welding mask with a thick slab of pilkington glass, before going anywhere near the power switch.

I laughed at him the first time I saw this, and he told me a story about some lab tech in the states in the mid eighties who had an "accident", the first thing the beam encountered was matey's protective goggles.

it burnt a hole in them.........


8
Class 1


A class 1 laser is safe under all conditions of normal use. This means the maximum permissible exposure (MPE) cannot be exceeded. This class includes high-power lasers within an enclosure that prevents exposure to the radiation and that cannot be opened without shutting down the laser. For example, a continuous laser at 600 nm can emit up to 0.39 mW, but for shorter wavelengths, the maximum emission is lower because of the potential of those wavelengths to generate photochemical damage. The maximum emission is also related to the pulse duration in the case of pulsed lasers and the degree of spatial coherence.

Class 1M

A Class 1M laser is safe for all conditions of use except when passed through magnifying optics such as microscopes and telescopes. Class 1M lasers produce large-diameter beams, or beams that are divergent. The MPE for a Class 1M laser cannot normally be exceeded unless focusing or imaging optics are used to narrow the beam. If the beam is refocused, the hazard of Class 1M lasers may be increased and the product class may be changed. A laser can be classified as Class 1M if the total output power is below class 3B but the power that can pass through the pupil of the eye is within Class 1.

Class 2

A Class 2 laser is safe because the blink reflex will limit the exposure to no more than 0.25 seconds. It only applies to visible-light lasers (400–700 nm). Class-2 lasers are limited to 1 mW continuous wave, or more if the emission time is less than 0.25 seconds or if the light is not spatially coherent. Intentional suppression of the blink reflex could lead to eye injury. Many laser pointers are class 2.

Class 2M

A Class 2M laser is safe because of the blink reflex if not viewed through optical instruments. As with class 1M, this applies to laser beams with a large diameter or large divergence, for which the amount of light passing through the pupil cannot exceed the limits for class 2.

Class 3R

A Class 3R laser is considered safe if handled carefully, with restricted beam viewing. With a class 3R laser, the MPE can be exceeded, but with a low risk of injury. Visible continuous lasers in Class 3R are limited to 5 mW. For other wavelengths and for pulsed lasers, other limits apply.

Class 3B

A Class 3B laser is hazardous if the eye is exposed directly, but diffuse reflections such as from paper or other matte surfaces are not harmful. Continuous lasers in the wavelength range from 315 nm to far infrared are limited to 0.5 W. For pulsed lasers between 400 and 700 nm, the limit is 30 mJ. Other limits apply to other wavelengths and to ultrashort pulsed lasers. Protective eyewear is typically required where direct viewing of a class 3B laser beam may occur. Class-3B lasers must be equipped with a key switch and a safety interlock.

Class 4

Class 4 lasers include all lasers with beam power greater than class 3B. By definition, a class-4 laser can burn the skin, in addition to potentially devastating and permanent eye damage as a result of direct or diffuse beam viewing. These lasers may ignite combustible materials, and thus may represent a fire risk. Class 4 lasers must be equipped with a key switch and a safety interlock. Many industrial, scientific, military, and medical lasers are in this category.

9
That's *NOTHING*

By the cubic foot acrylic isn't that cheap, but, you can do some really impressive things with it, my (final) conversion to digital photography came about because I made a very impressive coffee table for someone to their design, basically a stack of different shaped pieces in a very pretty very light green glass coloured acrylic all bonded together into one lump, doesn't sound like much but then neither does Bryce Canyon when you describe it as a bunch of different shaped slices of stone stacked on one another.

Anyway, being quite proud of it I took a whole reel of pictures of it once it was delivered and in situ in a nice modern setting.

Got home and discovered there was no bloody film in the camera.

Trouble is "we" generally only see the material used in cheapo cafe menus and things so we tend not to appreciate its various qualities.

You can cut / drill / mill / tap / bend / bond / polish it, only your imagination limits you.

I grew up playing with wooden blocks, my boy plays with flame polished offcuts, he isn't interested in cruddy wooden blocks when he can experiment with acrylic in various wired shapes and colours, all with kid safe edges, all hygienic, all unique.

Toys r Us got nothing on daddy's scrap bin... lol

10
Took about 2 hours, but then I have built them in the past which made it easy.

As for the acrylic, no, I buy mine from my local supplier (Plastexe) but it is a vastly under-rated material IMHO, incredibly versatile...








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