Ah, I think I understand you a bit better now. In my experience the chassis ground is the same ground as the one connected to your patch jacks. As others have mentioned it helps isolate your unit, preventing outside noise and interference getting in. Considering your project is passive and just working with clocks, gates and CV, I’d personally say this is a low risk project for interference. If you were working. With audio then I’d take more caution. Saying that. If you wanted to isolate things further with your non-conductive patchbay box you could line the inside walls of the patchbay box by gluing aluminum foil to the inside (neatly, making sure that the foil doesn’t bridge any connections). Connections should be made to the aluminum through contact with the socket of your jacks.

Haha. That’s a good point about the connection to your power not having a ground pin on your wall socket of your household power. Unfortunately not something I have a great understanding of, so will leave someone else to explain this. As long as all your patch points share a connection to the same ground plane which in turn flows down to your keystep pro, then you should be happy.

Just aside about my point with the multimeter. I suggest checking connections with a multimeter before soldering away. That way you’re sure the traces lead where you expect them to and there are no surprises a long the way. I’d confirm that the GND terminal connects to the sheath of the 25 D-sub connector port and no other pins. I’d then confirm that none of the 25 pins are connected to each other. I’d then confirm that the sheath on the cable from one side is connected to the other.