Also, if you have already drawn tracks for a net, and then decide to assign a net class with a different width and redraw the tracks, I found you must delete every bit of track linked to that net first, before drawing again, or it will not use the new net class width. (I assume that is not a bug, but expected behaviour.)
I had not noticed a bit of track on a far pin on the net and since it was my first time changing a net class width, I thought I was doing something wrong with net classes, until I finally noticed the little extra bit of undeleted wire…
Not with me. As soon as I change a netclass track width the track tool follows the new width.
Please supply your Kicad version and OS. Go to Help > About Kicad > Top RH corner click box titled “Copy Version Info.” and paste directly into a forum post.
KiCad has sort of 3 modes for determining track width.
Always use the netclass width.
Use a pre-defined track width.
Continue with the same width as an already existing track.
That is not true at all, and would also be silly. There are many reasons for wanting to use track segments with a width that is different from the netclass width. And if you have pre-defined track widths, you can even add hotkeys to change track width. While drawing a track you can also change the track width via the context menu.
If you’d really had to delete all track segments of a net before you can draw tracks with another width, then that would be a serious bug in KiCad. But for now I assume that it’s your inexperience in KiCad.
Wires are used in the schematic. On the PCB, KiCad uses tracks, (while many other PCB design program call these traces) Please try to be consistent in your terminology to avoid confusion.
Click on the button next to the track width drop down (which should be set to “Use net class size”); that button toggles whether to use the existing track width or to override it from the net class settings.
I expect I tried it when I was trying various things (learning how to use net classes), while I was unaware of a small segment of track on the same net, but a different part of the board.
I guess the wording “when routing from an existing track” in the mouse-over text, or “if the routing start point is the end of an existing track” is somewhat unintuitive for the case where you are not routing track from any existing segment of track, but there is a bit of track for the same net somewhere else on the board. Would that copy/documentation clarification be something that should be reported as a bug? (Of course, I know how difficult it is to explain anything complicated in a mouse-over text.)
I think it is fairly safe to assume that this function is only suitable “when routing from an existing track”
How could this function work if there is no existing track from which to route?
I tried and could not reproduce it, so it was just beginner confusion.
It must have been that one of the bits of tracks leftover was going from the same pin, even if in another direction, and I had the U button turned on. Thank you for your help!