My PCB requires a mounting slot connected to the ground. I know how to use grounded mounting holes, but I can't figure out how to produce the desired result using a single slot. Is there a component in some library that I could use? Or do I need to define the shapes using the Pad (17) and Milling (46) layer? If so, how should I set up the shapes so that the fab house understands that the slots are to be plated?
Perhaps this guide from Autodesk titled "What you didn’t know about EAGLE: Slotted Holes" could help: https://www.autodesk.com/products/eagle/blog/what-you-didnt-know-about-eagle-slotted-holes/
My PCB requires a mounting slot connected to the ground.
Eagle does not offer an tickbox for slots. You have to do this yourself.
You can do this in two ways:
1. Create a rectangle on the outline/milling layer, and tell the fab house to mill it.
2. Create a rectangle on the drill layer, mark it, and tell the fab house to mill it.
If you want plated slots, make sure copper overlaps with said rectangle, on top and bottom.
Is it sufficient that the copper overlaps the milled area? Or do I need to instruct them explicitly?
You have to tell them explicitely. Some fabs offer online tooling for you to designate and mark outline or milling objects. Like Eurocircuits PCB Solver.
Beware that depending on plated or non-plated the capabilities of the milling can be different. In terms of minimum size (often 2mm), radius and precision.