At 02:34 PM 6/18/03 -0400,
JanRwl@... wrote:
>That kind of plotter may be fine for plotting graphics on PAPER, but I'd
>never consider one for plotting something that required the mechanical
>resolution
>of a PCB, particularly a double- or multi-sided one!
>
>If your need is "professional enough" that you require plotter-drawn artwork,
>then you must simply go BUY what you need!
>
>If your need is avocational, and/or only very occasional, the use of
>manually-applied Bishop Graphics PC-component patterns to 0.1" grid paper
>is not yet
>considered a mortal sin!
>
>An acquaintance who worked for a large chemical firm GAVE me a like-new 7475
>that his employer was "throwing out"! I removed the cover to clean it with
>solvent, and dust-out the innards, and I saw that it moved the paper with
>RUBBER
>ROLLERS, and the quill across the page with a RUBBER "timing belt" with
>considerable "wiggle and flop". And both of those axes were moved by
>little DC
>servo-motors with "shaft encoders" and custom "electronics". This may
>have been
>an acceptable mechanism for moving a felt-tip pen about on smooth paper, but
>NOT for plotting something like PCB art! NO way! Now I grant you, I DID
>repeat the buillt-in Demo-Plot on the same sheet of paper, and it repeated
>all
>probably within 0.01", or even better---hard to tell, running a PEN about
>over
>paper! I put an ad on e-bay, and sold it to an artist in a State far, far
>away
>in a few hours! NO regrets!
Come on now, Jan.
I most respectfully must disagree with you on this topic.
I (we) used our HP 7475A plotter to plot the artwork for hundreds of
layouts - most were plotted at 2X size and reduced to 1X negatives by our
local print shop.
The only problem we had was with the pens clogging midway through the
plot. Accuracy was excellent for boards up to 5" x 7" (10" x 14" plot
size). We used both standard carbide tip and carbide cross-groove pens
plotting onto mylar.
The rollers that move the media are not rubber: they are sintered metal
wheels with ∗very∗ sharp teeth. These teeth imprint the media so that it
does not shift about: when you load media into the plotter and start a
plot, the first action the plotter does is move the media from one end to
the other. This imprints the tooth pattern on the media. That pattern
functions somewhat like the perforations on tractor fed fan-fold computer
paper and helps keep the media in the same location.
As you mentioned, repeatability was better than 0.01" over the length of
the plot. Reduce your artwork by 50% and that error drops to about
0.005". This is definitely most acceptable, even by today's standards.
That 'timing belt' that moves the pen holder across the paper is even more
accurate: repeatability is somewhere around 0.002" over the full width.
The main reason we moved over to an inkjet plotter (Pacific Data Protracer)
was because of the pen clogging problem I mentioned. But I keep that old
plotter handy - it gets used several times a year for odd jobs.
dwayne
--
Dwayne Reid <
dwayner@...>
Trinity Electronics Systems Ltd Edmonton, AB, CANADA
(780) 489-3199 voice (780) 487-6397 fax
Celebrating 19 years of Engineering Innovation (1984 - 2003)
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