I have read some posts on this, and it seems you can’t add a pad/hole directly in the PCB editor, one has to create a foot print first, then add that.
Okay so if I create a foot print, add a pad, and set Pad Type to NPTH: Mechanical, then surely it should gray out Pad shape and Pad size X, since it is a mechanical hole? What is the different between a through hole and a NPTH Mechanical hole?
When I set the pad size smaller that the hole, because it is just a mech hole and it warns me: “Warning: Pad drill will leave no copper or drill shape and pad shape do not overlap.”. Is that not what a Mechanical hole is?
And under coper layers if I uncheck F.Mask and B.Mask, and select Copper layers: none, I get an error: “Error: pad has no layer.”. Is that not what a NPTH Mechanical hole is?
The file format always expects these values and the user interface basically exposes all values without abstraction to the user.
The warning in this case is misleading. The problem of making it smaller than the drill is that DRC will not take the hole into account.
A hole affects all copper layers. After all the drill goes through all of them. (Again DRC needs to know that)
Similarly to the mask layers. You don’t want mask to cover the hole so you want it removed -> Mask is a negative layer so ticking it ensures that mask is removed where needed.