In normal drawing mode the line thickness is shown in real size, as set and as if in scale 1:1, regardless of the size of the drawn objects or the intended scale. So if you have a relatively small object you will easily notice differences in line thickness, while in a drawing of a large object like a building the lines all will seem very thin unless you zoom in very, very closely. Only in print preview mode with scale set properly, for instance 1:100, line thickness is shown as expected for print out, as in this mode line thickness is used in relation to paper size units.
Thank you for the both answers the problem was I couldn't draw on one file thick lines been searching for the reason, checking the setup of the files found the one I could draw thick lines
had the Units Preferences to “None” the other was setup to “Meters”, changing to None then it
worked but the little window to enter thickness is still in “mm” I work in metric “Meters” now what should I do.
Is there no other way to work with this? Is this a bug in LC.
Disappointed I worked with other CAD programs most on Meters and never had problem like this.
It is standard to define line thickness in mm, at least in the metric world. That's from old times when you were drawing with real ink pens on real paper. So you don't have to consider scaling line thickness according to the drawing's scale. I don't know a cad system where this different. Some more advanced systems offer something called in Autocad polylines, which means a pair of parallel lines with maybe a black filling in between. You could use this for example to draw walls, in this case using meters for the broadness would make sense. Librecad does not yet feature this kind of polylines.