I think I will leave the project as it is now.
Laser engraving and cutting works just as with a normal laser machine with the same power.
The only problem with this setup is, with the laser dot moving away from the center it gets out of focus. This is because the setup is missing a F-theta lens. I didn't use one because they are really expensive and I couldn't find one for 450nm wavelength.
̶m̶̶a̶̶y̶̶b̶̶e̶̶ ̶̶i̶̶t̶̶ ̶̶c̶̶o̶̶u̶̶l̶̶d̶̶ ̶̶b̶̶e̶̶ ̶̶p̶̶o̶̶s̶̶s̶̶i̶̶b̶̶l̶̶e̶̶ ̶̶t̶̶o̶̶ ̶̶c̶̶o̶̶m̶̶p̶̶e̶̶n̶̶s̶̶a̶̶t̶̶e̶̶ ̶̶f̶̶o̶̶r̶̶ ̶̶t̶̶h̶̶e̶̶ ̶̶f̶̶o̶̶c̶̶u̶̶s̶̶ ̶̶s̶̶h̶̶i̶̶f̶̶t̶̶ ̶̶b̶̶y̶̶ ̶̶c̶̶r̶̶e̶̶a̶̶t̶̶i̶̶n̶̶g̶̶ ̶̶g̶̶c̶̶o̶̶d̶̶e̶̶ ̶̶w̶̶i̶̶t̶̶h̶̶ ̶̶a̶̶ ̶̶l̶̶a̶̶s̶̶e̶̶r̶̶ ̶̶s̶̶o̶̶f̶̶t̶̶w̶̶a̶̶r̶̶e̶̶ ̶̶w̶̶h̶̶i̶̶c̶̶h̶̶ ̶̶c̶̶a̶̶n̶̶ ̶̶m̶̶o̶̶v̶̶e̶̶ ̶̶t̶̶h̶̶e̶̶ ̶̶z̶̶ ̶̶a̶̶x̶̶i̶̶s̶̶ ̶̶a̶̶c̶̶c̶̶o̶̶r̶̶d̶̶i̶̶n̶̶g̶̶ ̶̶t̶̶o̶̶ ̶̶p̶̶o̶̶s̶̶i̶̶t̶̶i̶̶o̶̶n̶̶.̶̶ ̶̶b̶̶u̶̶t̶̶ ̶̶a̶̶t̶̶ ̶̶t̶̶h̶̶e̶̶ ̶̶m̶̶o̶̶m̶̶e̶̶n̶̶t̶̶ ̶̶i̶̶ ̶̶h̶̶a̶̶v̶̶e̶̶ ̶̶n̶̶o̶̶t̶̶ ̶̶t̶̶h̶̶e̶̶ ̶̶c̶̶o̶̶d̶̶i̶̶n̶̶g̶̶ ̶̶s̶̶k̶̶i̶̶l̶̶l̶̶s̶̶ ̶̶t̶̶o̶̶ ̶̶w̶̶r̶̶i̶̶t̶̶e̶̶ ̶̶o̶̶n̶̶e̶̶,̶̶ ̶̶s̶̶o̶̶ ̶̶i̶̶ ̶̶w̶̶i̶̶l̶̶l̶̶ ̶̶l̶̶e̶̶a̶̶v̶̶e̶̶ ̶̶i̶̶t̶̶ ̶̶a̶̶s̶̶ ̶̶i̶̶t̶̶ ̶̶i̶̶s̶̶ ̶̶f̶̶o̶̶r̶̶ ̶̶n̶̶o̶̶w̶̶.̶
Just had an better idea:
Maybe a focus lens on a motorized carriage could keep the focus right while the beam lenght (lenght between galvo mirror and workpiece) changes.
With an autofocus a Z axis would no longer be necessary for different workpiece thicknesses.
I think I will add that on the next galvo laser project.
I added the .stl files and the .ino file for the converter board and will add the components list soon.
If someone is interested in building one and needs additional infos let me know :)
(If there will be more interest in it I could also write building instructions for it.)