spot sizes for different lenses

[brian257]

Can anyone tell me what should be the diameter of the focused beam from a typical K40 tube with the 38.1, 50.8, and 63.5mm focal length lenses and what the diameter of the unfocused beam is? I am trying to cut some small apertures in thin plastic and i would like to undersize the drawn holes by the correct amount to account for the beam size.

[daniel.macke]

Hello,
The best way to know the offset to apply is making a test cut :
Using the same material and settings (cutting speed, laser power, lens, focus distance, air assist...), cut a round or square hole with exact dimensions (for example 10mm)
You just have to measure what you get to know the correction to apply. You can even check the difference between the top and backside, of course it is more important with thicker materials or shorter focus distance lens.
Usually, the "width" of the cut will vary from 0,2 to 0,6mm, so you need to offset the original shape by 0,1 to 0,3mm to finally get the exact dimensions.
Regards.
Daniel