Werner Almesberger wrote: > > Hmm, I'm a bit worried about components that are specified > in metric units. The next best imperial grid size still > yields an error of 1.6%. > > I haven't tried to complete a layout yet, so maybe I'm just > too paranoid. Don't worry. Many or most commercial designs these days use some parts with metric-pitch pin layouts and others with imperial-pitch layouts. So there is no grid that is exact for all components. That's annoying, but it's a fact of life and people do manage to make boards that work.
And even if you were able to design on an exact metric grid, the output device (photoplotter or printer) is quite likely to use an imperial grid internally, so there would still be a conversion step. .007" is a typical minimum feature size for ordinary PCB fabrication. We have had reasonable results using a .25mm grid and a .254mm (0.010") track size. That works well for surface mount components with 0.5mm pin pitch and also for ones with 0.050" pitch. As a related side topic, think how much easier things would be if the base unit of length in the metric system had been equal to an imperial inch. The great advantage to the metric system - the consistent power-of-10 relationship between units - is unrelated to the choice of the fundamental length. There is nothing especially compelling about 1/10,000,000 of the distance from the equator to the pole as a fundamental unit. The meter is not particularly convenient for measuring things at the scale of human bodies - which is the scale that matters to people most of the time. I am 1.88 m tall, or 6'2". It is much easier to think about small integers than decimal fractions. If power-of-10-scaled inches were the basic unit, then I would be 7.4 decainches. 7 decainches would be an ordinary height, 6 would be on the short side, 8 quite tall. From an engineering standpoint, there would be no discrepancy between small grids. And many wrench (spanner) sizes would be the same between the decimal series and the fractional series. I expect that, had the base length unit been the inch, the imperial system would be long gone by now. But considering the political tension that existed between France and England in the 18th century, it's difficult to imagine the French Academy of Sciences using an English unit! Politicians have wars and the rest of us pay the price. Please read the Kicad FAQ in the group files section before posting your question. Please post your bug reports here. They will be picked up by the creator of Kicad. Please contribute your symbols/modules to the library folder in the group files section. For building Kicad from source and other development questions visit the kicad-devel group at http://groups.yahoo.com/group/kicad-devel Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/kicad-users/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
