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SKILL BUILDER: Clear Prints
capturing air, this won’t be the case, and you’ll
need to set the ironing flow to zero.
The bottom surface might be a bit trickier. In
order to get a smooth, glassy bottom surface,
you need to print on something with a smooth
and glassy surface. Glass is the obvious choice
— but PETG prints on bare glass have a tendency
to stick too well and occasionally pull a razor-
sharp shard of glass off with them. Using glue
or hairspray as a release layer would cloud
the surface. PEI print surfaces are common,
but PETG also tends to stick too well to those,
especially the smoother ones, and the high
temperatures involved will make it worse. What I
found worked best was a strip of polyester-based
high-temperature masking tape.
PRINT COOLING
Print cooling also makes a big difference. Once
the plastic leaves the nozzle, it immediately starts
to cool. As it cools, it shrinks, so the more it cools
between layers, the more plastic you’ll need to
put down to fill the space.
On one printer, I needed a flow multiplier of
111% with my cooling fans on, but I got even
better results by turning the fans off and
lowering the flow rate to 98% (Figure
C
).
Even with the space filled, the fan-cooled prints
were more cloudy than the prints that were kept
as hot as possible between layers. This means
that you not only want to turn the cooling fans
off, but enclose the printer for best results, to
slow the natural cooling. This slower cooling also
means that the cooling from one layer to the next
will be more consistent as the area of the layer
changes, which makes it more useful for printing
things other than calibration cubes.
UNIDIRECTIONAL PRINTING
When I read Ryan Cooper’s (Rygar1432)
recent guide on Printables (printables.com/
model/15310-how-to-print-glass), I was
surprised by the suggestion that you should
avoid printing layers in alternate directions. I
had previously used alternating directions, and
thought that method would make it easier to fill
any small gaps in the previous layer. When I tried
the unidirectional method though, I found that
it did help, for a few reasons (Figure
D
). First,
if any gaps remained, they lined up every layer,
creating lines of non-transparency instead of a
grid. Second, it meant that plastic was added to
Fan on at 111% flow (left) vs. fan off at 98% flow (right).
C
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