Printing Eifel towers

It seems almost all FDM (Fused Deposition Modelling) printers are very good at printing their 'logo-model'. These are as a rule, small, symmetrical objects. And that's no accident: due to the thermodynamic limitations of the printer's concept, non symmetrical object warp out of shape quite quickly, while printing. Only at very low printing speeds, more complex non-symmetrical objects can be achieved. To sum it up: the Eiffel tower is the wet dream of any 3D printer: perfectly symmetrical, designed to counteract all warping stress within the model.

That's pretty visible when one watches the '3D printing Star objects': as a rule, these are perfectly symmetrical objects (Martin Zampach's vases and lamp shades are a nice example):

This has to do with FDM technology: similar to a hot glue gun, the print head is layering heated plastic. These layers shrink while cooling down, causing the object to warp out of shape, especially when it's not symmetrical.
In order to print quicker, these layers have to cool down almost instantly before a new layer is applied. If not, the next layer will smear into the previous one, resulting in a pastic blurb.This cooling process - with some ventilators attached to the printing head - is very difficult to manage: it depends on the shape itself, room temperature, the plastics used and even the color (black radiates heat quicker than white).
Warping can cause the object to detach itself from the base, resulting in 'spaghetti in outer space'…


Calibrating the FDM printer as such is a very haphazard process, which has to be redone for almost each different object, each material, each color, each room temperature… At least, it teaches students (and teachers alike) to work in a very methodical organised way. Logging all the settings and their results, is crucial.

That's the inevitable thermodynamic paradox of FDM 3D printing: plastic should cool down from some 200°C to room temperature instantly, which of course, it doesn't. Especially in larger objects, where heat accumulates during the printing process, it will ruin the print. The only solution is slowing down the proces to an excruciating slow pace: printing overnight to produce one, small object is the rule, not the exception.

Will FDM printing revolutionise 3D prototyping? Definitely not, in spite of the popular press. But it will become a fascinating designing tool, with it's own weird limitations and rules. It can produce some marvellous object, but the machine (and technology) itself dictates to a large extend the rules of the designing game. Well, that's not so different from fresco-painting, after all…

Peter Missotten nov. 2016