Co2 Laser focus length

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Freddie
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Co2 Laser focus length

Post by Freddie »

I recently fired up a 80 watt Co2 600 x 900 laser. The previous owner gave me the gauge to set the focus length to 55mm. I engraved an emblem I designed, but the laser lines were wide and "fuzzy". I tried re-focusing by a few mm, but no improvement. I experimented with focus length, doing a test fire after each adjustment. At around 75-78mm the laser dot seemed most clear. This put the laser barrel tip about 1" above my work. I re-engraved the emblem with much improved results. I suspect the previous owner may have been using a 75mm lens as he was cutting 1" styrofoam for shipping boxes.
I have 2 questions, how will know what lens I have, and does it take a different laser head barrel for the longer focus length?

I will order a 20mm x 50mm lens for engraving if that is my issue. Is it ok to engrave with a 75mm focus length lens?
Tech_Marco
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Re: Co2 Laser focus length

Post by Tech_Marco »

You may taken off the laser tip and fire a laser shot with Lowe power say 8%. Move your laser head up and down until the laser dot appears to be the small dot you can get. Then, measure the distance from the dot to the lens, that will tell you the focus lens. it may not be exact but there is a standard size on lens spec. which popular of 38.1mm, 50.8mm, 63.5mm, 68.5mm, 75.0mm. There is other spec like 25.4mm 100mm, 150mm, and 200 but not very popular.

You can't simply use a 68.5mm in place with 58.5mm laser head, doing so will cause laser beam hitting the barrel and got less power or no cutting power at all.

Please take a picture of your laser head.


Marco
Techgraphix
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Re: Co2 Laser focus length

Post by Techgraphix »

General you may say that a short-focus lens is better for engraving and a long focus lens is better for cutting as the Depth of field is much larger.
Although i use a 38.1 (1.5") lens i have no problem cutting 6mm (1/4") acrylic
To find the exact focal length you may use a Focus Adjustment Ramp:
FAR2.JPG
FAR2.JPG (70.09 KiB) Viewed 2572 times
It doesn't need to be that beautiful.. This one does the same job:
FocusBlock.JPG
FocusBlock.JPG (62.82 KiB) Viewed 2572 times
Kees
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