This was a quick test of assembling aluminium parts.
As one can see in the lower left corner of this structure, the crossbrace, is intersecting through the sideplates. The hole i milled for the sidebraces has extended radiuses so that they can be filled with weld. i Used TIG for this one, that left a super clean, nice weld. After welding, i milled it away, to leave a flat and nice surface.