A revised version of my 2020 Frame corner design. With this version each piece of extrusion is contacted by three screws in a triangular pattern, the same pattern for each piece, and the part has been shortened in height reducing contact on the vertical extrusion.
Print at 40% for Strength, PLA is fine
Layer height at 0.2mm for screw hole/countersink accuracy
M4 Metric Screws with 2mm Countersink
Channel slots for tight and square fit
Each Aluminum piece is contacted by three screws in a triangular patter for max rigidity
Maker Architect (Replicator 1 Clone w/ Heatbed)
0.2mm layer height, 40% infill, 215C InLand PLA