Bad print quality on small lines/area's/bridges + Custom made adjustable Z-endstop

My <5mm = bad print quality issue

While printing smaller objects the prin quality is really bad. Rounded corners that should be straight corners, ugly 5mm bridges while I can print a perfect (imho) 50mm bridge. etc.
So i've asked the people on the RepRap Forums for their experienced advice...

Custom made adjustable Z-endstop

A friend created a custom made adjustable z-endstop in a fancy CAD program. The print is not perfect yet (due to the issue described above) but a second version of the STL files is coming soon. If it works out fine I'll post the STL's on thingiverse!