Digital BW, The Print

----- Original Message ----- 
From: "Paul Roark" <paul.roark@...>
To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
Sent: Friday, August 01, 2003 6:47 AM
Subject: RE: [Digital BW] Coating - again...


> Tom,
>
> >>...I'll go to thicker glass and paper.  However, when I was
doing the
> >> experimenting, all the 16x20 prints were made on the 3000,
> >>which just does
> >> not handle thick paper well enough to bother with.
> >
> >> Paul
> >> http://www.PaulRoark.com
>
> >Why thicker glass, Paul?
>
> It looked like the center and edges of the print were not
getting the same
> amount of PUR.  I thought that could be from the 1/4 inch
glass, which was
> on a towel and supported by particle-board, might be sagging or
otherwise
> not being totally parallel to the rod.  I think Diversified's
literature
> indicates that the set-ups they sell use thicker glass.  On the
other hand,
> it could be that a 1/2 inch rod is not sufficient to span a 16"
print
> without bending slightly.  Unfortunately, the thicker rods get
expensive.
>
> Diversified also has a pad that can be put under the paper.  I
think the
> "softness" of the support is a variable that might need to be
explored.  As
> I understand it, these long rods are not usually used on hard
surfaces.  I
> think the medium is often dragged across the rod with a
flexible web.
>
> I didn't do a lot of  experimenting with 16x20 prints.  I tried
a few, was
> not satisfied with the results, and ran out of time to do more.
I think the
> rod & PUR deserve more work, but I just have not had the time
for some
> months.  A thorough search of how industry uses them might give
some hints
> as to what is needed to get good results.  Robert probably has
the most
> experience with the rod and large prints, so searching his
posts would also
> be a good idea.
>
> Paul
> http://www.PaulRoark.com

Paul,

I've been thinking about another setup since we discussed the
coating technique ages ago. What you experience with larger
images is what happens with most manual coating systems and
similar mechanised ones. Not just bending of the table top or the
rod but also the force you have to apply with wider rods, longer
strokes, constant speed is asking for another method. Like in
most printing methods it is a easier to achieve equal pressure
between two cylinders over the width and the length of the
stroke. Probably over the top for 16 x 20 but who knows what is
next.

So a setup with a cylinder in bearings below and the fixed (so
not rotating) rod above with pressure control like an intanglio
press has some benefits.
The difference being that the pressure can be much lower than in
an etching press. To get the sheet coated you could use a
polyester sheet of precise thickness (most are as they are often
used for film mounting etc), and on that the to be coated sheet
taped at the start. Bring the polyester sheet between the
cylinder and the rod. pour the coating in front of the paper and
pull the total through the slit, a handgrip bar at front and
along the width of the polyester sheet will make it easier.
Another bar at the other end of the sheet to stop the action.
having this pressure unit (temporarily, think "table tennis net")
in the middle of a table you can use it in two directions but
then you need another method to fix the paper than taping it.

The diameter of the cylinder below can be measured to the width
of the paper to get stiffness. There's literature enough how
printing press cylinders are constructed but I guess with the low
pressure needed any cylinder will be good. The bar diameter is
another matter as it also gives the coating thickness. But since
it isn't rolling it can get strength from a beam above with some
adjustable screws along its length. Quite a construction I agree
but I have sizes up to 2.5 feet in mind, for smaller sizes it can
be much simpler. With someone to help you you don't need a table
either in coating or just a small table. Simplicity and easy
deassembling is needed for cleaning the equipment. A wider
cylinder and poly sheet than the rod width helps there too.

I do have the parts more or less but little time. Then there's a
silkscreen machine in the shop, so I got an alternative. This
isn't a proven method but to let it linger in my mind without
mentioning it may not be good either.


Ernst