PSU-mounted Full ATX Test Bench

This design reduces the footprint of a full ATX build as much as possible while supporting large and heavy GPUs.  The PCIe/GPU side of the motherboard is fully supported by a bracket that rests on the PSU while allowing plenty of air intake, and the CPU end mounts to a support leg that spans the width of the motherboard.  Since the PSU goes underneath the full ATX portion of the motherboard, this design does not work with ITX and mATX boards (design for those here), but in exchange the potentially heaviest part of the board is well-supported.

To solve the problem that PSU length isn't standard, the design is modular and easily adjusted for specific PSUs.  Profiles for your typical 5.5-6.25" power supplies are provided, and the model is split into parts that can be moved in groups.

If you make adjustments, leave the standoffs and tall GPU mounting bracket in place since they are standardized, and do not adjust anything on the front side  (note: no width adjustment either b/c standard width is 5.9"). You'll want to move the BACK two corners and the back rail to fit the length of the PSU.  If you have a really long PSU you you will have to add some material underneath where the standoffs are - the 6.25" and larger designs have some basic shapes added for this purpose.

Use a material that can handle some heat like ASA or ABS (accounting for shrinkage), PETG should be fine too.  PLA is not a great choice since it will deform.

Note: the standoff screw holes are intentionally a little bit small so you can tap threads into them with typical computer screws (6-32 or M3) or any screws you may have lying around.