I wanted to fit a second RTX 4000 Ada 20GB GPU to my AI dev rig, based around the Fractal Ridge case. The Fractal Ridge has a room for triple-slot GPUs, and includes a riser for a single PCIe 16x slot, along with an extension piece. So put of the box, only a single GPU is supported.
I bought the C-Payne bifurcation adapter (https://c-payne.com/products/pcie-gen45-bifurcation-adapter-fpc-cable-x8x8-2w-2u-60mm) to split the motherboards' x16 slot into two x8 slots. My RTX 4000 are single slot blower style, so only take up a single slot, but I still wanted to leave a slot space between them, hence that specific bifurcator. The little extension riser board that Fractal supply is removed.
I wasn't happy leaving the GPUs floating around in the case only restrained by their expansion slot brackets. There is place to screw in a brace on the back of the cards (like how Dell do in their workstations), but that still didn't solve the issue of things moving around when plugging in and unplugging them from the bifurcation adapter, so I decided to build a base-plate to mount the C-Payne bifurcator onto the Ridge's riser plate.
FreeCAD was awesome for this - most of the time was spent setting up planes in the correct locations. I can't believe how far FreeCAD has come, and far fewer crashes that when I last used SolidWorks back in 2013/2014. I used the regular Creality slicer to print on my Creality K1C printer with PETG, which took around 2:30 hrs.
I put a little cut-out in the baseplate for the bifurcator to drop into, with some pins to hold it in the correct position. In the end I stuck it down with double-sided foam tape. The flexible PCIe ribbon is free to sweep around without bending too tight.
The outermost upstand on the side of the baseplate allows the use of fan-mount screws to hold it down through the Ridge's 140mm side fan mounts. That's the only downside - you sacrifice the 140mm side fans, but there is still room for 80mm fans at the top of the case, but it doesn't look like I need them anyway since the top of the case is so open.
If I was doing it again, I think I would use nuts and bolts (or put in some threaded inserts) to mechanically hold the bifurcator in place, but with double-sided tape and the GPUs screwed in place, it's all solid anyway. Either that, or make the mounting posts a bit wider so that they form a compression fit on the holes in the bifurcator PCB.
Overall, I'm happy with this, my first full design + print.
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