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Date:	Thu, 17 Jul 2014 09:10:04 +0200
From:	Gabriel Paubert <paubert AT iram DOT es>
To:	geda-user AT delorie DOT com
Subject:	Re: [geda-user] Gerber Export Generates Abitrary Drill Tool Numbers
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On Thu, Jul 17, 2014 at 09:12:26AM +1200, Lilith Bryant wrote:
> On 2014-07-16 10:52:53 PM, Gabriel Paubert wrote:
> > I've never need more than 6 drill size on a given board, how often 
> > have you made a board with 10 or more different drill sizes?
> 
> My last board had 12.   The one before that had 13.
> 
> And both of those were after rounding to the nearest 0.1mm
> 
> If you have a lot of different connectors, you get a lot of different 
> sizes.

Ok, you have a point, most of my connectors are now SMD and I try to limit
the variety of connectors in a single design.

This said, it was also probably the weakest of my arguments. You simply
can't mixup Gerber photoplotter files and Excellon drill files, therefore
independent number spaces should never cause a problem. 

A limit of 255 drill sizes for a single project is probably more than 
sufficient: on a metric setup drills are typically produced by steps 
of 0.05mm (and I'm not sure that 0.05mm is available), so this gives 
you all sizes by steps of 0.05mm up to 12.7mm. 

The fab I currently use does not allow drills above 6mm (larger ones 
are milled and cannot be plated, so they should be specified by the 
outline layer). Smallest holes are 0.2mm (0.1mm with surcharge).

There are ~120 drill sizes between 0.1 and 6mm, so the limit of 255
should never be reached in practice.

	Gabriel

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