I downloaded and printed the most commonly used 3030 Angle from Thingiverse but I was not happy with it. A few issues really frustrated me.
The 2 x Right angle sections were too thick and the screw could not pickup the nut when the nut was in the bottom of the channel.
The 2 x 45 degree braces were quite thin and have been increased in width to 5mm to provide extra strength.
There was a recess behind the screw holes which significantly compromised the strength of the item around the screw holes.
- The items would not fit neatly into the corner as the right angle corner needed a slight chamfer.
All of these issues have been corrected.
Print with the long surface on the bed and the right-angle up.
3 x Top Layers
3 x Bottom Layers
3 x Perimeter Layers
I use PETG.
Designed with FreeCAD on a Mac