> If you are a software guy, drilling a 12mm horizontal hole 30mm deep into the edge of a 20mm x 400mm plate is surprisingly difficult. It won't fit in my drill press that's for sure.
Welcome to the wonderful world of jig-making. "Making" jigs has about the same amount of "making" like "coding" in programming. You have to invent or search for a jig which will make that task doable. I suggest clamping lightly two planks to sides of your plate, make a thick block with your desired hole, then screw that block onto planks so that your hole is centered between them. Now you have a guide for drill.
Welcome to the wonderful world of jig-making. "Making" jigs has about the same amount of "making" like "coding" in programming. You have to invent or search for a jig which will make that task doable. I suggest clamping lightly two planks to sides of your plate, make a thick block with your desired hole, then screw that block onto planks so that your hole is centered between them. Now you have a guide for drill.