Hi Brad,
Honestly, I don’t believe that you have a defective unit at this point!
The focus is paramount.
When the G2 arrives, the user needs to stick on the measure tape on the Z-Axis. If one does not do this accurately, you cannot go by that to set the focus.
What you describe how it works if you move around the focus height completely makes sense in this regard.
Do this please: start an engraving that takes a while. Move the focus up and down until you get the strongest burn. - This is your focus height. Review our video about Galvo focus: https://www.youtube.com/watch?v=wOEdciQtPVI
Then you can move the measure tape on the Z-Axis to zero.
You can then go by the ruler to set the focus. The more accurate way to set it is by aligning the two red dots.
This was not set up correctly when I first used my machine either so you need to adjust this by loosening the screws of the brass-colored red dot laser on the galvo head and move this brass ball until the two red dots are aligned perfectly at the correct focal height.
I was unable to find any instructions from Gweike about this process and if you don’t feel comfortable doing this yourself, I recommend reaching out to Gweike.