Designing a simple photo frame. I wanted to make it so that it prints without supports. While printing, however, the back support part wobbles/vibrates with movement, and is printing terribly.
Ender 3v3 CoreXZ, PolyTerra matte black filament, using the CR-PLA Matte profile in Creality Print 7. Tried printing at slow speeds, the issue still persists.
I’ve tried making the back support with only 45 degree angles (previously it was an x diagonal), made it thicker (from 0.75mm to 1.5mm). Nothing is working. Please find the stl and 3mf here (https://www.thingiverse.com/thing:7281179).
Is this a printer issue, a model issue, or a slicer issue? Please advise. 
Thanks for the pointers. I tried 45 print, and the vertical part broke off within the first inch or so lol. Should have tried at low speeds, because until it broke, it looked pretty good. May be that filet could have made it not break off that way.
Yeah the most valuable skill when designing parts is to learn how to design for the process. Print orientation should be decided in the earliest stage so as to maximize strength where it counts, reinforcements to compensate for layer lines weakness should be baked in. FDM prints behave like wood: strong across the grain, weak through the grain.
If it wasn’t for the groove, my first advice would have been to redesign the part so it could be printed sideways.