I have an old habit from my days of PEAD (Pencil & Eraser Aided Design): draw a skeleton of what you want with a bunch of hairlines with appropriate offsets and trace what you need with a thicker pencil. Mark hole centers etc same way.
Today I need to create my first own footprint totally from scratch.
I have a DS for the part with a bunch of dimensions and I was hoping to repeat the technique.
But where is “Add dimension” button in footprint editor?
Or there is something that I am missing on the concept level of footprint editor?
I don’t think there is such a thing in the Footprint Editor.
What you can do is use the “User” layers to add some lines to help a bit with alignment.
Or indeed the good old paper and pencil to make a sketch.
Dimensions in the Footprint Editor are often a bit different from shown in the datasheet. For example, the Footprint Editor likes to know the center locations of pads, while datasheets may specify the edges of pads. Pre-calculating the numbers KiCad likes and writing them down beforehand make it easier to focus on entering the right numbers in the right locations in the Footprint Editor.
A completely different option is to use the “StepUp” workbench in FreeCAD. It has quite a learning curve, and I mention it more for completeness then as a suggestion.
At least in v5 the kicad internal options were too limited to be of use. Which is why i always used external tools to make the drawings needed for checking contributions to the official library. I documented my workflow here Tutorial: How to check footprint correctness?