Homebrew PCBs

Thanks Tom,
That was very informative.

I only have a 30" fl lens for my CO2. I have good results with 
cutting .125" pvc, acrylic and similar materials. I don't have a good 
ventillation system, so I avoid too much plastics cutting (at least 
until I get better ventillarion and compressed air system).

Would you say that an investment in a 5" FL lens (or beter) would do 
a better job for me? I only intend cutting .125" material.

I have tried cutting the FR material, but I get too much charring 
with the low power.

You can drill a BARE FR board before it gets copper plated. Then send 
it through the through hole plating facility and plate on the needed 
copper.

John M...
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--- In Homebrew_PCBs@yahoogroups.com, "twb8899" <twb8899@y...> wrote:
> 
>  
> > What power CO2 laser do you need for cutting 3mm 
> steel/brass/aluminium?
> > I've got a two-stage pump that can go to 10^-4 torr. I'm 
designing a
> > cnc x-y table...
> 
> I had a Mitsubishi CNC Laser for several years and have some 
> knowledge of how they work. This machine was a model 1212HC with a 
> 3000 watt resonator and 48" x48" cutting table. The entire machine 
> installation was the size of two pickup trucks. 
> 
> We used this machine mainly for cutting small stainless steel and 
> acrylic plastic parts. When cutting .060" stainless steel the power 
> levels would vary between approximately 400 and 700 watts depending 
> on cutting speeds. The CNC program would change power levels when 
> needed. Lower power and table speed is used for fine cuts with 
higher 
> power and feed rates for everything else. 
> 
> A coaxial beam of cutting gas is always used with CNC CO2 lasers. 
We 
> used oxygen for most steel and stainless and sometimes nitrogen for 
> stainless cutting since it leaves a cleaner cut edge. Clean 
> compressed air or nitrogen was used for cutting plastics.
> 
> Acrylic plastic cuts well with compressed air and 75 to 150 watts 
for 
> up to .125" thick and around 200 watts for .250" thick. The power 
> level, frequency, duty cycle and gas pressure was fully adjustable 
> (even while cutting) and allowed precise control of the cut quality.
> 
> Since most of our work was small parts with fine detail we used 
short 
> focal length lenses. A 5" focal length lense was used for most work 
> and a 2" lens was used for super fine cutting on thin materials. A 
> 7.5" lens was used on materials over .25" thick and up to .5" thick.
> The longer focal length gave a straight cut through thicker 
materials 
> but had a wider kerf (cut width) in the material being processed.
> 
> One time we tried cutting some FR-4 double sided laminate and it 
> didn't work very well. It took about 900 watts to pierce through 
the 
> top copper layer and then the glass epoxy exploded into a blob 
since 
> the power level was so high and was also being reflected back from 
> the bottom copper layer while piercing it. 
> 
> Non-ferrous metals such as aluminum, copper and brass take much 
> higher powers levels to pierce and cut on a CO2 laser. My 
experience 
> was that the same power level to cut .375" steel could not even 
> pierce through the copper on a circuit board. I don't think the CO2 
> laser is the best choice for cutting PWB laminates. Maybe the YAG 
> machines will do a better job on circuit boards.
> 
> Tom