I designed this bracket to use with my TEVO Black Widow 3D printer, but it could be useful for any project using V-Slot extrusions. I am using these brackets in conjunction with aluminum L plates, but I included holes and space for T-nuts so they could be locked in place themselves.
Print with angled side on bed as in the STL. No supports needed. Use raft/brim as needed for your printer/filament. I suggest 0.25mm layer height or less if using standard 0.4mm nozzle.
It might take a little "finesse" to insert it into the v-slot the first time, but once you insert it and slide it a bit the fit is snug but not too tight to move around.