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Message-ID:	<4F9BFF5D.9010407@schinagl.nl>
Date:	Sat, 28 Apr 2012 16:31:57 +0200
From:	Oliver Schinagl <oliver+list AT schinagl DOT nl>
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To:	geda-user AT delorie DOT com
Subject:	[geda-user] Metric vs Imperial, Grid snapping
Reply-To:	geda-user AT delorie DOT com

Hi list,

this time, somewhat unrelated question.

Someone on this list posted a link to Tom Hausherr's blog about PCB 
design and that was an incredible interesting read.

A few things he mentioned that where extremely interesting was his post 
about metric usage vs imperial usage of parts etc [1].

Here it is mentioned that metric is the way forward in PCB design and 
far it allows for far higher accuracy eventually. I'm sure hobby usage 
won't need/'allow' such high accuracy, most hobby PCB houses don't have 
equipment that does these high tolerances, but even so.

Why is gEDA/PCB by default using the imperial system? It's quite easy to 
change, absolutely, but if it is actually recommended to use 
millimeters, why 'force' a default of mil's? Even if it is somewhat 
autodetected from the system's Language, mm should be the default, no?

Also, he mentions using 0.05 mm routing grid as most component lead pin 
pitches are 0.05mm. My first design I used a grid size of 10mil's 
because that was the default. I used 8mil widths for nearly everything 
as seeed's minimal width is 6mil. 10mil was the closest for the grid. I 
guess the question is, what grid size would be recommended, depending on 
the fab house's tolerances?

Oliver


[1] 
http://blogs.mentor.com/tom-hausherr/blog/2011/03/31/inch-to-metric-conversion-tables-for-pcb-design/

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