Re: [CAD_CAM_EDM_DRO]Printing/Plotting grating

"D.F.S." wrote:

> >
> > Rather than a 300 dpi inkjet, some of the old pen plotters are good
> for
> > 0.001--if you can come up with a really fine pen tip. Some of the
> newer
> > laser and inkjets are supposed to be better than 300 dpi.
> >
>
> I thought we had all this nailed down before.
>
> As to the plotters, mine have, and I think the the HPGL standard is, a
>
> language "resolution" of .001.
>
> The reality is the mechanics are nowhere near, and no even multiples
> or even fractions of that resolution.
> It more like call for a move to 3.000 X 4.000 and it will move there,
> give or take 20 thou ;-).

My Calcomp plotter has a servo drive, and the encoder resolution is, in
fact,
1 / 2056 of an inch. But, that is resolution, NOT accuracy! With pens
not made
much smaller than .012" wide, and who knows what actual ink line width
you get
from that pen, it still isn't much good. I have a laser photoplotter
that has a resolution
of .001", with a gaussian spot size of .001", and a total accuracy of
better than
.005" over the whole machine's work area, and it STILL is woefully
inadequate
for making encoder gratings! Now, a machine like this, but 30 feet
long, could
make a master pattern that could then be photographically reduced to the
size
needed, like a 3' long scale.

> I would not bet on a single pixel printed on a page to work.
> Ie. 300 dpi in no way could ever do even 150 Lines/Inch IMHO, 75 would
>
> be a longshot at 2 pixel wide lines and here's the kicker I ran into
> 2 pixel wide spaces without bleedover.

That's why you use an 'analyzer' grating, so the results of a 1 mm or
2mm
spot can be averaged, reducing the effects of small errors in the scale
and
dust specks.

Jon