Issue
You have received a DWG file, with line weights and colors set specifically to match your Archicad project's Pen Sets. You only need this DWG as a tracing reference, so your preferred import method is to 'Drag and Drop' or place it as a Drawing.
You will notice that after placing the DWG in Archicad as a Drawing element, the Pen color will be the closest match in RGB values, but the Pen thickness is completely disregarded.
Solution
Essentially, with this import method, the DFX/DWG Translation Settings will not be taken into account. Instead, Archicad will consider the Pen Color's RGB values (connected to Pen index values), and exclude Pen thickness.
Consult this article if you want to know more about each DFX/DWG import method, their benefits, and limitations, and their Translation Settings.
And to understand more about Archicad's translation of Pens and Colors consult this article.
What we can do to fix the appearance of the inserted Drawing is the following:
- Select your inserted DWG and open the Drawing Selection Settings
- Under Pen Set, I click on the button View Drawing's own Pen Set
- Click on Add to Project...
- This allows us to save a copy of the Pen Set to the Archicad Project's Pen Set
- Then in the Pens & Color Manager, find your newly saved Drawing's Pen set, find the Pens used by the DWG and modify the thickness of those to your desired value
- Go back to the Drawing's Selection Settings and under Pen Set change from 'By Source File' to this modified newly copied Pen Set.
- The Drawing will automatically select the best RGB match available in the new Project Pen Set
This might add a few steps to your workflow, which might not be desirable, but it will fix any precision issues you might face when tracing over the wrong pen thickness.