When I hit the button “Set Origin of Grid”, a circle with a cross move to that point, but
the positions, x,y,dx,dy still measure against a point somewhere outside the sheet.
How can I set the origin to the point I need it?
The coordinate origin is the (top,left) corner of the sheet.
You can select everything in your design (big selection rectangle) and move it wherever you want.
Since you can’t move the origin, move everything to the origin and the result is the same.
The other confusing thing is there are two user settable origin points. The one described “Place the origin point for drill and place files” sets the origin for manufacturing files, but the other which I think the OP means is described “Set the origin point for the grid” and does something different, it just sets an origin for the on screen grid.
The latter I find useful with the relative coords, and pressing space at the origin sets the relative origin. This effectively gives you an extra coordinate space for lining up components and features, and also makes it easier switching between mm and inch.
I didn’t know that the [space] needs to be pressed to put the origin of a relative system indicated by dx,dy to that current cursor location. Definitely makes work easier.
Another thing I do when laying out my PCBs is to set a corner of my PCB to be a nice round number, like 50,50. That way, it’s easy to work out distances in your head. Then the additional dx/dy/reset with space is another set of coordinates you can use. I find the latter very handy for lining up components.
If you already have a design layout and want to move it, you can use the dx/dy to work out the delta between where you are and where you want to be. Then select all and do a Ctrl+M / “Move exactly” and put in the deltas so your board lines up exactly at the chosen nice round number.