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I have long since discovered that despite having a pretty
large chase area (~7x11), the Pilot is quite limited in how
much total pressure and thus printed area it can manage if you
want an even and full impression. I've done quite a few jobs
where I was really pushing the limits of the press. When you
get in this situation, the time you need to spend adjusting
platen jack screws, cutting and pasting many layers of
overlays, and fine tuning the packing to get a good print can
easily grow into multiple hours for one setup. As the total
pressure climbs for a larger printed area, the press parts
start to deform unevenly and this leads to a lot of fiddling
and makeready to compensate. If you are printing with black
ink or don't care what the shade of the color comes out to be,
putting more ink on the press helps with this. But if you are
trying to get a pantone color, loading up the disc with ink is
not a good option since then the color will come out way too
dark.
For this job, I was using a fairly textured and not very soft
paper from Paper Source, which needs relatively more pressure
to print than something soft and creamy like Somerset
paper. Also the printed area of the block with the trees and
lanterns on the main card is in retrospect too big for the
Pilot to do well. The main card is 5x7.
The job that broke the Pilot's back
PDF Version
So after a lot of fiddling and setup I got things arranged so
that the print was reasonable, though it still could have used
a bit more pressure. I started printing, and as usual with a
large printed area I was nearly hanging on the end of the
handle to make the impression. I got through about 80 cards
when I head a big pop during one print. At first I couldn't
find anything broken, and I thought maybe a tool had fallen
onto my metal cart or something. Soon enough it became obvious
what had happened though; the main right side casting had
cracked where one of the shafts goes through.
Boo Hoo!
Zoomed out view of problem area
Needless to say this is a very distressing development. My
feeble attempt to doctor it up with a hose clamp was totally
useless. I have a heavy duty U bolt coming from McMaster
tomorrow that I will try, but I don't have high hopes. I can't
believe I was able to break that casting with just manual
pressure. Even with the leverage of the handle, I can't have
been putting more than 180lbs on the handle since thats how
much I weigh. I'd have to analyze the linkages on the press to
calculate mechanical advantage, but it couldn't be more than a
factor of a few x. The section of the casting that failed was
about 0.5 x 1 inch, and some quick web research says gray cast
iron should have a min. tensile strength of around 20,000
psi. Bugger!
Anyone know of a good place to get castings repaired? If I
can't find a replacement or a good place to get it fixed at
reasonable cost I guess I'll try to braze it at home. Given
that cast iron is notoriously finicky to repair, I don't
relish that prospect. Or maybe I can mill off the stump of the
broken casting and fab a big plate of aluminum or something to
bolt onto the side of the casting and capture the shaft. None
of that stuff sounds good to me though... Dang.
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