Laser Optics

[thejuggernaut]

Hello all,

I have been doing research and would like to begin a large co2 laser build. I have decided the 1200 X 1800 gantry as the platform I would like to build. My first question is about laser wattage. I would like to be able to cut up to .75" acrylic, and balsa for RC airplanes (hobby of mine). Speed isn't that important, but I would like to be able to cut on a single pass. Secondly, I'm kind of confused about optics. I have a basic understand of the mirrors and the lens setup, however I am confused when it comes to beam expanders and combiners. How do you add a standard red laser to the setup? Would it be better to have a stationary laser tube, or one that is mounted to the moving gantry? Is there any literature you can direct me to so that I can learn all of the aspects of the optics involved in building a basic 2 axis CO2 laser?

Regards,
Taylor

[Tech_Marco]

It is very difficult to cut a thick acrylic in 0.75" (19mm) unless you have higher power laser tube and longer focus lens.
I'll have to say that you need at least a 75mm focus lens in order to get decent flatted cutting surface with possible about 10 degree inclination. If it is acceptable, then take 75mm. Otherwise, you need 100mm focus lens. But longer focus lens need more power to sustain the longer beam. I won't use 100mm if you don't have 130W or 150W laser tube installed. Plus, longer focus lens (over 75mm) need special tip for the laser head.

1800x1200 XY stage is considered a very big stage. Think about the travelling distance and you may concern that the longer distant it travel, the weakness laser power occuried. Assuming "Top Left" is the HOME position aslo the shorter travelling distance zone, then the "Bottom Right" corner is the area where the weakness beam most occured. Laser power lost at that region could be as much as 15~20% when compare to the closer area, the Upper Left corner.

Beam expander is used to expand the light beam diameter wider accordingly. It helps to improve the beam collimation and at the same time to reduce stress on the mirror & lens. It improve engraving performance a lot. Some said that it boost power as much as 20~25%! But the draw back is that since the beam diameter is wider, the beam angle is sharper.

I'll get a beam combiner with red dot laser built-in soon. You simply installed right in front of the laser tube and made some angle adjustment, then the red dot will show exact point where the CO2 laser beam is hitting at.



Marco

[thejuggernaut]

Thank you for the reply. 3/4 was a more a goal than a requirement. Maybe a little unrealistic. Realistically I believe that 1/2" would be the thickest I would ever be cutting. I'm making a list of all the things I need and plan to start buying up parts as money permits!

Regards
Taylor

[Guldberg]

We cut 20 mm acrylic with a RECI W6 130w tube. We use a 100 mm lens and cut at 2 mm/s. It works, but you dont get that nice polished edge as you do in 10 mm.