Hi John,
Generally, I look at precision as it relates to mils (.001 inches)
Concerning the precision (and range) of numbers required for photoplotting,
drilling, routing, etc. I think the following applies:
In inches, 2.4 number format seems suitable. That allows numbers from
99.9999 inches down to 0.0001 inches in increments of one tenth of a mil
(one ten thousandth inch).
In millimeters, 4.3 seems suitable. Converted to inches, that allows
numbers from 394 inches down to .00004 inches in increments of 4 hundredths
of a mil (4 hundred thousandths of an inch).
Hope I got all my "ths" right.
Also, leading or trailing Zero suppression in gerber or tooling files
minimizes file size.
Also, I've never liked 2.3 format (inches) for gerber files. image
distortion can result from the rounding.
Regards,
Mark
-----Original Message-----
From: John Foster [SMTP:[log in to unmask]]
Sent: Wednesday, December 04, 2002 2:12 PM
To: [log in to unmask]
Subject: [TN] Question about resolution
It seems that there are a lot of very experienced fabricators in
this forum.
I have learned a great deal from reading the posts.
I started laying out boards in 1998, it is not my chosen profession
but is
starting to become my chosen profession. I enjoy it very much. When
I started a old manufacturing engineer gave me a set of guidelines
to follow
and something's I am still figuring out on my own. With that said
here is my
question to the forum.
Right now I am sending all my gerbers and drills out in millimeters
in a 3,5
274x format.
So that means I am calling out things at 1/100,000 of a millimeter.
I know
that this has
to be way beyond etching tolerance and what a drill can hold on
tolerance.
This is kind
of what I started with. I have begun to change all of my designs to
a .05
millimeter grid.
But I still have some old legacy stuff from when I really didn't
know what I
was doing.
So my question is what is realistic. At how many decimal places in
millimeters or mills
does it become nonsensical and a waste of time for the guy or
program that
has to
round everything off.
What kind of tolerance can a modern drill hold?
At what point does the photo plotter or direct imaging machine run
out of
gas?
Once again I have learned a great deal from this forum and would
appreciate
any kind of response
Thank You
John Foster
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