Friday, 15 February 2013


The 'Sun worship' model took me at least five attempts to get a decent print from, but having finally got it to the point where I was happy with the output quality I decided it was time to move on and try a different design.

There are many factors to consider when designing a model for printing on a 'fused filament' type of 3D printer, like a RepRap or Makerbot. One of the most important ones is the the need for 'support material'.

The printer starts printing the bottom layer onto a flat bed (usually heated to 100°C to make the plastic stick to it) and then proceeds to print each successive layer on top of the one underneath. This works fine for blocks with straight sides and can even cope with sloping sides of up to 45 degrees where each layer projects out a bit further than the one below.

But in real life, things stick out at all sorts of angles and this presents a problem. Just take a look at the middle of your face and imagine how difficult it is to print chins and noses. The printer is squirting hot, runny plastic filament downwards from the nozzle and needs something to extrude the plastic onto. If there is nothing there, the string of plastic will just hang down in mid air instead of following the path that the nozzle is tracing as it draws.

Sun Worship

One way to address this problem is to create support structures which are not part of the sculpture, but are solely intended to provided a surface for the upper layers to land on. 
Another way is ensure that the model has no projecting angles shallower than about 45 degrees.
Look again at the Sun worship model and you will see that all of the limbs, the torso and the head have been carefully posed to ensure that there are no unsupported regions.

I decided that my next project would be a nude sculpture of a woman standing in a pensive pose, one knee slightly bent and arms held close to the chest. 

After working through a number of iterations I arrived at this pose.

Again I spent a considerable amount of time fixing the mouth and eyes and creating a customised hair object.

It turned out that there were several problems with this model. Firstly, the points of the elbows and the chin had nothing beneath them so I decided to add some small support blocks for removal after printing.

In this picture, you can just make out the small disc between the thumbs, as well as the triangular elbow supports.

This should have worked in theory, but in practice the chin support was too thin and failed to print correctly, while the elbow supports ended up too close to the model and caused an unsightly mess.

The other big problem was that my printer can only go up to a height of 13 cm and even using the full print height the model still ended up quite small.
This would have been OK had it not resulted in the fingers becoming too thin to print correctly.
Here is one of the early attempts demonstrating some of these problems.

I made a number of significant changes to try and improve the quality of the print.

  • Moved the elbows closer to the abdomen and removed the support blocks
  • Repositioned the thumbs under the chin
  • Slightly fattened the fingers and thumbs
  • Increased the height of the model to 20 cm
  • Printed in two halves, with a connecting pin to join them back together
The fingers are little bulky and the seam is still visible but this is straight off the printer, with no post-processing work.


Incidentally, you can see the legs of this model being printed in the very first picture of this blog.

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