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View Full Version : 2" vs. 4" FL engraving



Zsolt Paul
02-23-2010, 5:26 PM
Does anyone have any experience engraving with 4" lens? I generally use 2" for engraving and 4" for cutting, however there are times I had used 4" for engraving due to the longer focal length, it works better when the material is slightly uneven or not 100% flat.

I haven't done a real comparison test, but I am theorizing that the 4" would also create smoother engravings in acrylic for example and especially for 3D wood carving due to the larger spot size. Its a little like putting the 2" out of focus. Perhaps a 300 dpi engraving would look more like a 400 dpi in terms of "smoothness" or not seeing the engraving lines b/c the spots are more overlapping. Am I right? IF that's the case, what would be the advantage of using a 2"? Besides a more concentrated power from a 2", which I almost never need anyway, having a 100w machine. Is there a rule of thumb when a 2" must be used (or better) and other times when a 4" is more advantageous besides the reasons I mentioned above?

Zsolt Paul
02-23-2010, 11:01 PM
Nothing? Nobody uses 4" FL around here?

Rodne Gold
02-24-2010, 12:32 AM
I use a 4" lens , it's not good for engraving if you want detail. You can achieve the same "smoothness" with a 2" lens if you defocus it a bit and have the benefits of significantly more energy density in the spot.
If you want smooth large frosted areas and you dont need great depth , then a good strategy is to make those areas a shade of grey rather than a solid colour as the laser will then engrave this as a halftone which will stop the ridging.

Albert Nix
02-24-2010, 8:43 AM
I have one and like it if I am not worried about supper fine detail. I use it ever so often with the rotor attachment when I have some with a small in it so that I can focus and not worry about clearance. It would make sence that the optics would say cleaner being farther away from your work but I am not sure it really helps.

Richard Rumancik
02-24-2010, 11:22 AM
The 4" lens is really considered a cutting lens because the spot size will be pretty large. Maybe .008 diameter or more? I'm not sure exactly. But placing .008 laser "dots" .0033" apart (300 dpi) means a lot of overlap. Seems to me that the image would be pretty fuzzy. That is not to say that you can't use it for special purpose engraving - by personally I have not found an application. If you had a deep bowl and wanted to engrave inside that might be the only way to do it - but then 300 dpi might be too high.

I use the 2" for general cutting but prefer 1.5" for marking and precision cutting of light materials (films, thin plastics, veneers). Lots of people here don't use the 1.5".

I have used the 4" for cutting 1" thick light urethane foam (used for inserts in equipment cases). It works quite nicely for that as it has a large depth of focus.

Zsolt Paul
02-24-2010, 2:20 PM
Thanks for the replies. I should have clarified that I was thinking about using it for text. I can see that for photos or anywhere shading is desired the spot size would overlap too much and the defenition would get lost in the picture.

I was about to engrave into a 24 x 36 in acrylic. Its text only, all 100% black. The sheet had a little bit of a bow. THe 2" being so much more sensitive to the object being flat due to its lesser depth of focus and since its all black, I was thinking in a case like that the 4" would be perfect. It would allow for the slight up and down play in the material and I could even lower the resulotion due to the larger beam size and get the job done faster.