Re: [CAD_CAM_EDM_DRO] Laser Project ( was Re: Laser links ?

> Also with a target of 6 months to a year, I have pleanty of time to
> get stuff on the cheap. E-bay and the like.

The main things to look for on ebay are power supplies and vacuum pumps. I'd
avoid the second hand optics and just buy new ones. Hair-line cracks with
finger prints and you're talking waste of time.

> Which style laser ? CO2 or YAG ? other ?

There are two styles that'll emit IR that you can make 'easily', they are
CO2 and the Nd's. There are different sorts, Nd:Glass Nd:YAG (Neodymium
Doped Yttrium Aluminium Garnet) and Ruby. The YAG gives the most optical
energy out but it's also more expensive. One of them, I don't remember
which, takes longer to cool also (I am testing my memory but YAG I think).

It's essential to remember that high frequency pulsed crystal lasers, like a
YAG, are going to be:
A.) Very tricky to set-up and maintain in respect to timing
B.) Expensive
For an example, the typical home made power supply and cooling for these
rods allows one shot in anything up to a minute. There is no way on Earth
you'd cut anything with that. The high frequency YAG lasers are still fairly
new technology. The only possible way for you to get it is to use a Q Switch
from a tank's range finder (The M-80 Hughes).

I would go with CO2 for sure.

> What makes one harder to implement than the other ?

Mmmm, that's kind of answered above. They each have their own tricker parts.
Crystals will come with plated, mirrored, ends so you don't need to align
them. But their power supply is tricker and they need some excellent cooling
for high repetitions or the crystals expands and fractures, which = major
problems. A rod the thickness of a pencil and 5cm in length is in the range
of $400 - 600. CO2 you have the small problem of mis-alingment on the
mirrors since they need to make the light resonate inside the cavity and
should be parallel to each other. But realistically that's nothing compared
to the crystal rubbish you'd have to do. The supply is brutally simple too,
a neon sign transformer! :-)

> more costly to run ?

Potentially CO2 if you want a flowing gas tube. After the molecule of CO2
has been pumped and emitted the light as it's electrons drop down the
orbitals, it then takes a little more time from then to return to it's
ground state. That can mean with real high power lasers you get stagnation,
gas that's not ready to be re-pumped (By pumping I mean pushing the
electrons up and out in the orbitals). They solve that by making the gas
flow to constantly fill the tube with fresh gas already at ground. I think
on the very expensive ones they might use roots blowers to recirculate it
but I'm not sure. Even if you bought genuine CO2 laser mix at £50 a bottle
it's not going to go through a bottle in less than a few months to a year if
you seal the tube and build it well (No leaks).

YAG use pricey flash lights and the crystal itself and these things are
delicate. A bump in the wrong place and you could fracture them. If you want
usable power from a single crystal at home you're really putting lots of
eggs in a metal box, resting them on a washing machine and hoping they don't
brake. Once you have a hair-line fracture it's useless since the rod will
most likely not lase in a correct fashion, and so have poor beam
characteristics, or split when it warms up. I saw a man at a laser show I
went to throwing around a rod the thickness of a marker pen and 20cm long
that was fractured inside. You're not really meant to even touch them
without gloves on and then you do it gently.

> This thread has made comments about the two, but some hard data would
> be needed. for my app, (glass) seems yag is no good.

YAG is the one you should aim to use simply because it's more efficient at
conerting the pump light's output into the sprectrum you want. However, you
pay for it, and it's going to be a painful expirience building a supply to
do the work of a CO2 laser on a YAG for you at home. These lasers are
usually in welding robots because they can have their frequency, pulse
length and all the likes changed about them. Their output is shorter than
CO2 as well and it can be sent down fibre optics round mad angles to a weld.
But unless you have a serious need for that mirrors will do fine for a
couple of bounces.

> What power is needed ? seems cutting a 1/4" steel plate would be
> about right for a home machine, although scaling anything up or down
> would not be too hard to do.

200 watts is about the maximum home brew guys will build their's too.
Slowing down and inputting more heat for the area will increase the cut
depth available to you of course but at 200 watts I think you'll find you
can move mighty quickly on anything other than metal.

> If my math is right, a 2kw laser might need a 20kw power source. I
> have 220 at home so 20,000 watts / 220 = 91 amps ? I'm not sure if
> my electric meter spins that fast.

2kW is extreme. There is no way on Earth you'd need a laser that big to cut
the work you want to do at a speed you can achieve. It's like buying a steel
working machine cell to make a cardboard box. I doubt you or anyone else on
here could find the money to build such a laser at home; Except maybe those
guys with Haas centres in their sheds! :-) 2kW output is A LOT of power
indeed. If you have a look on the internet you'll find pictures of people
running 100 watt tubes, even that is enough to fuse a brick into a glass
form where the beam strikes it. Just to boost your confidence, there is a
lad called Robin on the net somewhere who was 17 when I spoke to him last,
when I was 14, and he's making a superb looking CO2 laser by himself. He
should have finished by now.

Have a look for the laser group called CO2 Laser Growers.

John H.