Machine Selection

OK, so I know what I want to build, and why I want to build it. The next step is to decide what printing technology I want to use. The first thing to look at is the different technologies that a home builder can achieve with good results and within a reasonable budget.

There are many different technologies used in 3d printing, some more exotic than others. For this reason I'm going to limit my choice to 2. This is mainly to ensure ease of construction, at the same time stretching my abilities and learning. The technologies I will look at are: -

- Stereolithography (SLA)
- Fused deposition modelling (FDM)

How all current 3d printers work

So, a 3d printer constructs a real world object by building it a layer at a time. Once the layer is complete the printer moves by a fraction of a mm in hight. The next layer is then built directly on top of the previous layer. This process is repeated until the 3d object is complete. How the layer is constructed and the material the object is made from is where the technologies differ.

Stereolithography uses UV curable resin as its build material. It is placed in a bath where it comes in contact with the build platform, this is where the object will be constructed. A UV laser traces the layer using a series of mirrors that are attached to galvanometers allowing them to move in the X and Y axis. The printer then uses the process described above until the object is complete. Once completed, the object is removed from the build platform and rinsed to remove any excess resin which would spoil the print if left behind. Finally the object is placed in a UV oven to harden completely.

Image Source: http://www.solidsmack.com/fabrication/stereolithogrphy-110-micron-old-world-laboratories-nano-3d-printer/

Another method involves using a a modified DLP projector. In this method instead of the laser drawing the layer, the projector exposes the whole layer at a time. This speeds up the printing process considerably. The construction of this machine is also simpler as there are fewer moving parts. The complexity comes in the form of software.

Firstly an application is needed to divide the object into its individual build layers, also know as a slicer. Most slicers that I have investigated convert the object to gcode, a format mainly used in CNC and FDM machines. Secondly, controlling the projector and the timing of the movements of the build platform seem to be a bit of a barrier to me.

Image Source https://code.google.com/p/lemoncurry/wiki/main

Fused deposition modelling or FDM uses a thin plastic type material, also known as a filament as the build material. This is fed into a heated nozzle forcing a string of melted material to be placed on the build platform. The heated nozzle, also called an extruder is then moved back and forth to draw the layer very much like an etch-a-sketch. As before, the build platform moves a fraction of a mm and then next layer is drawn on top until the object is complete..

Image Source: http://www.hotcopier.com/fdm-printer

A variety of materials are available to print in at substantially less cost than UV curable resin.

Although the print quality is not as good as SLA, FDM printing has a well established ecosystem, which is good if you need help fixing something.

For this reason I have decided to go down the route of an FDM printer, specifically a reprap Rostock delta printer. I have selected this printer for it's simplicity in construction, large build area and support in the reprap community. Additional benefits of this route also include faster time when compared to traditional X/Y configurations and the reprap's ability to replace many of its moving parts due to clever design. For more on the reprap community visit www.reprap.org

Image Source: http://www.reprap.org/wiki/Rostock