INSERTION PRINTS #2 -
BOTTLE-IN-A-SHIP
 
by Erik Es - Amsterdam, July 5, 2018
 
Apart from my fascination for ships in bottles
(see INSERTION PRINTS #1) I had another
reason to create the 3D printed ship-in-a-bottle.
I wanted to finally bring to life an idea which I
had AGES ago - to make a bottle-in-a-ship.
Does humour belong in 3D printing ?
Yes, it does.

This turned out to be a lot harder than the
regular ship-in-a-bottle. The reason for this:
you can not print any desired shape as a
hollow object.

This is because the print is built up in layers
from the bottom upwards. So printing a cup is
no problem: first the bottom is printed, then the
wall of the cup grows upwards, no problem.

The problem is the top. Or sometimes it is.
With some objects, hollow printing can be done
without too many problems. (If you know all
about "bridging" you probably want to skip the
next bit.)
 
 
BRIDGING

For example, it is possible to print a hollow
cube. The bottom is printed first, then the walls
(from bottom top top), then the printer starts
printing the top. There is nothing to support the
first layer of the top as the printer is crossing
over the hollow inside - the printer is extruding
molten plastic into thin air.

However, this produces thin strands of plastic
that get spun over the top (a bit like a spider
does), providing the distance to be crossed is
not too high. This is called "bridging".

This first top layer is quite irregular -
sometimes a few strands are broken, and they
tend to sag... However, it provides some
support for the next layer, which is printed at 90
degrees across the first top layer.

Because of this support, this second layer will
be less irregular. And the next one will be much
better again. After a few layers there is enough
support for the rest of the top to be printed with
a clean finish on the outside. The "saggy" first
layers of the top are now hidden inside - unless
you are using transparent plastic for the print.

Another example: you can also print a hollow
cylinder with a dome-shaped roof. In that case
there is no need for bridging. The printer will
print bottom and wall, and will then start to
"shrink" the deposited circles as it finishes the
domed top.

So that's two examples of objects that can be
printed hollow. The same can be done with
many other shapes: a cone, or a pyramid,
or a quartz crystal, or a church - all possible.

But there are plenty of objects that are
impossible to print as hollow prints. Example:
the same domed cylinder as before, but with
the dome upside down, like an upside-down
beer can. Here's what happens:

At some point the printer starts to print the first
layer of the hollow dome: just a small circle,
right into empty space. There is nothing to
support it, and it is not bridging from wall to
wall. So all that happens is that some blob of
extruded plastic will end up in the wall of the
cylinder as the printer continues with the next
layer.

The same thing will happen in the next layer,
and all the ones after that. So you get no top,
just a messy cylinder. In this case a solution
could be to add a central pillar inside the
cylinder - but then it is no longer a fully hollow
object...

A similar problem occurs if a flat top of an
object has holes in it. Bridging is a nice trick,
but you can't expect these spider strands to
suddenly end in mid-air and then pick up again
as the print head passes across the place
where there is a hole in the top...

So I had to take all this into account while
designing the ship, because it would need
to be printed hollow.


Here's the ship I made:


As you can see, the deck of the ship forms a
curved top that closes the hull. The hull must
be hollow to hold the bottle. The bridge of the
ship needs to be hollow as well - looks much
better and saves a lot of print time compared to
a solid block. The bridge has a flat top, so
bridging is no problem there. The chimney is
also hollow and has an open top - no problem
either.

However, there was one problem to be solved:
the top of the hull is curved. It had to be,
otherwise the boat would look stupid. But that
slightly curved top would cause some nasty
problems when the bridging occurs.
The "ceiling" of the inside of the hull would not
look pretty, and that would definitely be visible
with the ship being transparent.

I managed to solve this problem. How I solved it
is a lot of tech-babble which I will save for
another blog. The short version: I made the
model in such a way that the bridging will
always happen "port-to-starboard-and back".

To make a nice set I decided to use the same
shapes for the ship and the bottle in both the
"regular" and the "goofy" version. With one
exception: the bottle that goes into the ship
does not have a flat side, so it can roll around
freely inside the ship. Here you see some
bottles being printed:


Next the ship is printed. Inserting the bottle into
the ship (just before the top of the hull starts to
close up) is MUCH easier than inserting the
ship into the bottle (the "regular" version),
because in this "goofy" version the bottle is
small and the hull of the ship is much larger,
as you can see here:

After the insertion, the bottle gets blown around
by the cooling fan in a dangerously frantic
dance, as if it is trying to escape the imminent
enclosure... But as the deck closes up, it
settles down, enclosed forever inside the ship.

The ship needs just a little bit of clean-up work
after printing due to some traveling (print head
jumping from one part of the print to another)
and then it is done:

A bottle-in-a-ship. Yippee - a very old idea,
finally did it !

Just one of many great 3D prints for sale at
Printed In Space.
 

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