If you have read the 'Welcome' article, you will know that desktop 3D printing is all about building up solids a layer at a time and that these layers are typically in the order of 0.3mm thick. Sometimes of course, the layers may be a little thicker - 0.4mm is as 'coarse' as we go - or perhaps more commonly, a little thinner in order to improve appearance at the expense of print time - 0.2mm or even as thin as 0.1mm. However, there are times when it is possible to print an object without using layers at all! At this point, the title of this article should give you a clue as to the alternative.
When there is no need for 'infill' which gives some solidity to an object and no need for the nozzle to move to a a different position without extruding plastic, it is possible to produce a 3D object by moving the nozzle in a very shallow spiral, extruding plastic as it goes. Typical candidates for this technique - spiralised printing - are things like vases which are hollow and have a single, continuous outer wall. The downside to this technique though, is that it is only possible to print the object with a relatively thin wall thickness - if the nozzle is 0.4mm diameter, the extruded 'worm' of molten plastic will produce a wall thickness which is not going to be much thicker than this. (OK - if the pitch of the spiral is infinitely small, we can get an infinitely thick wall but that would take an infinite time to complete the job!). In practical terms, it is reasonable to expect a wall thickness in the order of 150% larger than the nozzle diameter which makes 3D printed spiral vases good for holding most things but not necessarily water. (Although we have printed SOME watertight vases).
The thin walls of object printed using the spiral technique can be used to advantage - if we use a transluscent filament, spiral vases make great tealight holders. (LED tealights that is - we would not put a lighted candle in anything made of plastic).