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CNC manufacturing — additive

Additive manufacturing (or 3D printing) makes objects by layering successive stratas of materials to create the required shape. Conversely, subtractive manufacturing removes undesired materials to achieve the prescribed form.

Becoming more entrenched and cost effective, the rapidly developing additive/3D printing industry offers furniture construction solutions previously unimaginable. Those new to the subject can use the following publication (plus others listed in the sidebar) and essay to help with the learning curve.

3D Printing for Artists, Designers and Makers (2018), by Stephen Hoskins, professor at University of the West of England, Bristol, UK. Includes a chapter with several case studies of contemporary designers using 3D printing.

Furniture Futures and the Promise of 3D Printing (2018) by Berto Pandolfo, industrial designer and senior lecturer at the University of Technology Sydney.

From research furniturelink identified five major categories of 3D printers that produce objects in the required scale and materials (plastic and metal) for furniture applications.

  • Stereo lithography (SLA) — UV laser polymerized resin
  • Laser sintering (LS) — laser-fused polyamide or alumide
  • Direct metal laser sintering (DMLS) — laser-fused fine metal powders
  • Fused deposit modelling (FDM) — thin strand thermoplastic extrusion
  • PolyJet matrix — inkjet-sprayed UV light polymerized resin

furniturelink provides more information about FDM and Polyjet printing as two of the furniture designs below incorporate them.

Fused deposit modelling (FDM)

Example (below): Julian Goulding's Rise stool

The XYZ platform of FDM printers controls the position of a heated plastic extruder head (nozzle) that deposits a thin filament of melted plastic in a continuous process to form a complete layer. These inexpensive "desktop" printers can be sourced from dozens of suppliers. Prices start at less than $500 for the original kit form of RepRap printer. The popular MakerBot series ranges from the entry level Replicator Mini+ at about $1,200 (U.S.) to the recently introduced "performance grade" Method printer for about $7,000 (U.S). The new printer offers dual extruders and a dissolvable support system that allows parts to be printed with overhangs and cavities.

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The new deposit modelling (FDM) Method 3D printer from Makerbot (1)

However, the media hype and hyperbole around the FDM desktop printing warrants a caveat. The surface quality and mechanical strength of FDM printed objects don't (at present) match those of their injection-moulded cousins. Choice of plastic, melt temperature, nozzle speed, etc., improves the impact, shear and tensile strength of FDM parts. For safety reasons, though, FDM-printed components need thorough testing before using for load-bearing applications.

Mindful of the above, designers can use FDM printers as an inexpensive way to develop full-size prototypes of furniture components. A service bureau (see sidebar) with access to alternate 3D printing processes can produce the parts in a range of advanced plastics or metals.

FDM printer owners who may be tired of using plastic furniture hardware or fittings available only in white or black can print less stress-prone parts such as shelf pins, glides, grommets, pulls, etc. in a variety of colours. Many examples can seen on Thingiverse (a virtual "store" run by MakerBot) complete with the downloadable STL code (see Software below). For example Xacto makes available code for a 48 mm diameter two-part grommet for computer desk cabling.

Rise stool
The circular top (not shown) for Julian Goulding's Rise stool comprises three mortice holes that align with the tenons on the FDM printed top connectors. The three 530 mm x 22 mm diameter wooden dowels hold together with a three-axis FDM printed connector. The STL files can be downloaded from Thingiverse.

PolyJet matrix

Example (below): Tomas Rojcik's Peg chair

Ink jet nozzles in PolyJet printers spray a photopolymer in a very thin layer and instantly cure (polymerize) with UV light. Manufactured and developed by Objet Ltd., the company and technology merged with Stratasys, Inc. in 2012. This not-inexpensive technology produces a finely detailed finished part in a wide range of materials that can be rigid, flexible or a combination of both.

Peg chair
Tomas Rojcik made the corner connectors for his Peg chair in VeroWhitePlus (acrylic photopolymer) on a PolyJet matrix, Objet30 Pro printer. He designed the chair using SolidWorks 3D CAD design software and a set of four printed parts for approximately $500.

Robot extrusion

Example (below): Dirk Vander Kooij Chubby chair

Rise stool
Dutch designer Dirk Vander Kooij produces his entire Chubby chair in colourful thermoplastics. Using a extrusion nozzle attached to a robotic arm, he lays down his design in a continuous stream like toothpaste from a tube.

Software for 3D printing

In oversimplified terms, the software requirements for 3D printing start with the design's CAD file conversion to an STL format "g-code" file containing data for each layer (slice) of the object. The user then exports the file to the appropriate CAM software package (often proprietary to the printer manufacturer) that controls movement on the X,Y, and Z axes via the printer's stepper motors. See the sidebar for 3D printing software listings.

(1) Image © Makerbot

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© furniturelink 2018 (text) images © Julian Goulding, Tomas Rojcik and Dirk Vander Kooij