Yes I have seen this occur and believe it was due too some imported stuff on
an DXF file. We now do a cross check with the drill report and the printed
drill table.

Martin R

-----Original Message-----
From: Abd ul-Rahman Lomax [mailto:[EMAIL PROTECTED]]
Sent: Friday, February 22, 2002 12:28 PM
To: Protel EDA Forum

At 11:33 AM 2/22/2002 -0600, Bob Bauer wrote:
>I am a creature of habit. Since tape-up days, I have always created a fab
>dwg. It is a handy reference dwg for in-house use to double-check hole and
>board size. Our fab dwgs include the dimensions and hole count table, the
>layer stack and assignment, and any special notes that differ from our
>standard specs. I thought all board houses would require a fab dwg for
>reference to the data they have received. Or do a lot of them assume and go
>with the data at hand and if made wrong, it is the clients fault! I work
>very closely with my board houses, so that we both do not cause any

There are some of us who do not supply drill drawings. A fab drawing is a 
slightly different creature which happens to be relatively easy to make if 
one draws dimensions and notes on the drill drawing layer, but there are 
ways to use a mech layer for it, and some advantages to the latter.

Having a drill file, used to program the drills, and a drill drawing, which 
gives similar information (size is the important one, bombsighting now 
being used only where there is no drill file). If the two files differ, 
which one is the fab house to follow? It's like dual dimensioning; standard 
practice is to label one of them as REF. A good house will flag 
discrepancies, but it takes *time* to compare a drill drawing with a drill 
file, and that means money, and almost always it will be wasted. (Has 
anyone here seen Protel generate a bad drill file?)

Of course, the drawing may contain notes, like "Drill the nominal 0.125 
hole as 0.312."

Some of us also do not supply fab drawings, where a board is "standard 
production." Again, time is money. The CAD files do specify board outline 
if the outline is drawn on all layers, and a house like Advanced Circuits 
makes the materials, etc., to be used explicit as part of the order -- it's 
in the pricing model.

There is a place for such a relatively informal passing of information, and 
a place for very precise and specific formal drawings. If I were ordering 
$50,000 worth of boards, you could be sure that I would have formal 
drawings. And to avoid problems, redundant information should be labeled as 
REF or else a fabricator would have an out for supplying a board which 
followed one instance and not the other.

Hole charts are part of the fab drawing tradition, but using text with the 
numbers, I am suggesting, is more functional -- that is, easier to use for 
checking -- than using symbols or letters.

Abdulrahman Lomax
Easthampton, Massachusetts USA

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