VIRUS (part 2)
  by Erik Es - Amsterdam, August 7, 2018  
  I needed some strands of DNA for my model of a virus. 

(see: INSERTION PRINTS #3: VIRUS - part 1)

This posed quite a challenge. DNA is shaped like a rope ladder (as
used to board a ship or exit a hovering helicopter) which is first twisted
into a "spiral ladder" and then coiled up like an old-fashioned
telephone cable.

To achieve this shape (or something like it) I made a model that
consists of many small flat discs, each slightly higher than the next,
arranged in a "spiral staircase" shape. After many tests, trying out
different configurations and print settings like speed and temperature,
I managed to print a springy coil like this:
  The trick here is that each turn of the coil is laid down onto the one
below it. Finding the right speed/temperature settings was tricky: too
hot and the whole thing becomes a solid piece (as the plastic fuses
with the layer it is resting on), too cold and the spiral will not form in a
nice regular pattern. But after some persistent experimenting I
managed to get it right.

These coils are very springy. If you bend one and then let go, it
springs back and wobbles (like the spring you find in a ballpoint pen)
until it comes to rest in its original position. Cool. VERY cool... but still
too closely wound to look like DNA...

So next I dip them into hot water and then pull gently on both ends.
This causes the springy coil to stretch without breaking. Again it took
some experimenting to find the right temperature for the water, but
after some failures I ended up with the shape I was looking for:
  I then cut this spiral into smaller pieces which can fit into the body of
the virus. 

All that remains is to insert these pieces into the body while it is being
printed. As always with insertion printing, timing is essential.
There is only a small window of time to insert the DNA pieces - too
early and they will stick out too far at the top, so the print head will hit
them and fuse them into the wall of the print (start again...), too late
and the top of the virus is closing in too much, so there is not enough
space to drop the pieces in without them getting hit by the print head.

When I get it right it looks like this:
  To finish the model I remove the support structure that helped to
support the roof of the "mouth" part, and clean up the "fur" at the top
(caused by "cool head lift", meaning the printer pauses a few seconds
between layers and moves to the side, so the fan can cool the top,
before putting on the next layer).

Here's a picture of the finished parts:
  I then insert the 3 pairs of legs. The virus then looks like this:  
  Another amazing 3D print for sale at Printed In Space.

Next time you are suffering from flu, remember what amazing
processes are happening inside your body...