By Mario Pistone, Vice President, Parkin Architects Limited

Primer

This quick overview of the 3D print workflow will help you understand the content of this blog. The genesis of a 3D printed project is a computer-generated model scanned from an object or developed in a 3D program like Sketchup or Revit. The model is exported to another program (generally referred to as a ‘slicer’) to generate a layer-by-layer tool path and material supply code for the 3D printer to follow. The slicer may also calculate assistive tools such as temporary supports, pauses for material/colour changes and printer settings to balance speed and quality as desired by the user.

Once the tool path is created as a digital file, it is sent to the 3D printer, which then machines the model file from the loaded material.

Many of the principles in this blog are equally applicable to a variety of fabrication machines, however since the project covered in this blog was fabricated on an Ultimaker2 3D printer the blog is primarily focussed on similar 3D printer types (i.e. fused deposition modelling, or FDM).

FDM printers print by moving a material filament through a heated nozzle which then liquefies the material and lays it along a path in a thin layer. Cooling solidifies the material and the end result is the metamorphosis of the digital file into physical object.

Scale Limits

The scale at which a model can be printed is dependent on two key factors – the material used and the fabricating machine’s ability.

The material has physical characteristics that will affect its strength, warpage, and printability. The increasing array of plastics for 3D printing is continuously expanding the creative potential of 3D printing through introduction of a wide variety of material chemistries with a wide range of properties. Plastics are being formulated to glow, to react chromatically to sunlight and heat, to be conductive, magnetic, oxidize like iron, bend like rubber and be spongy like foam. Plastics are being mixed with wood, bamboo and even metallic powders and carbon fibre strands. Each plastic prints differently and needs to be accounted for in the 3D print model design and the printed scale.

The scale of the printed model will also depend on the machine fabricating it. The machine’s specifications will determine the finest detail that can be fabricated, the speed of fabrication and the ability to utilize the material effectively (which is also a factor of user experience in working with the material).

Nozzle Size matters

The most significant driver determining the print resolution is tool precision. For FDM printers, that means nozzle size. Since a modified Ultimaker2 printer is used for this project, there are a number of resolutions to work with. The extruding nozzle is interchangeable, providing a range of 0.25mm to 0.8mm of plastic extrusion width. This project is printed on a 0.4mm nozzle, which provides a balance of speed and detail for the scale of the model.

The precision of the build plate movement allows for each plastic layer to be as fine as 0.025mm (although a layer height of 0.1mm is sufficient for this blog’s project).

Each machine has its limits. Unsurprisingly, these limits are continually being overcome by technological innovation.

Rotary Place

This blog will explore the process for printing the south elevation of Rotary Place A (2009, Barrie ON).

Build Volume

To complete a model of Rotary Place, we need to determine the scale. At 1:200, the building elevation fits nicely in the build area for the South elevation B, however the build area is not sufficient to capture the longer north and south elevations C. As a result, the best scale at which to print the elevations, without the need for joining pieces together, is 1:250.

To determine how the elevation dimensions need to be refined to enable the reveals and relief features of the elevation to read in the 3D print, we printed a calibration model using a 0.4mm nozzle with an array of relief and reveal sizes (D & E).

As a result of the tool paths generated by the slicer, reveals and reliefs have differing detail levels. In the test print E, the 0.4mm wide relief was not printed by the machine, because the slicer software could not determine a valid tool path for the width.  However, at a width of 0.5mm, the relief successfully printed. Recesses were able to print at a finer detail, as demonstrated by the successful print of a 0.4mm wide reveal.

The test print demonstrates that at 1:250, the minimum scaled printable width of a relief is 125mm, and the minimum scaled reveal width is 100mm.

At a fine print resolution, each material layer is 0.1mm high (25mm scaled dimension at 1:250). One layer however, is not typically sufficient for coloured material to be seen opaque, and will be too subtle to readily read in the elevation.

In future blogs, we will experiment with layers of materials to create transparency, translucency and material colour representation. This advanced technique will require additional attention to thicknesses and widths.

After examining the test print, it was clear that a 1:250 print required exaggerated sizes of various components of the building, in order to print effectively.

• Mullion widths would need to be 125mm instead of 60mm
• Mullion depths would need to be 75mm instead of 20mm
• Glazing SSG joints would need to be 50mm deep to read effectively
• The glass canopy would need to be thickened to 125mm instead of 19mm
• Brick coursing would need to be increased to 125mm with a 100mm joint
• Panel reveals would be 100mm wide and 75mm deep instead of 15mm and 10mm respectively.

The resulting sketchup model does appear to have these exaggerated elements when seen at a small scale F.  However, a close up view G reveals the exaggerated elements that are necessary for the final print to read well.

Once the model is completed, exported as an .STL file and imported into the slicer software H, the tool path (red and yellow lines K) is carefully examined to ensure that the machine is capturing the level of detail.

After 81 minutes, the final print is complete L and ready to be mounted or assembled as part of a series of elevations to make a detailed model.