Machines and Tools
The joining system being made was within the Other Today Studio and as such was made to be a distributed design solution, meaning that the final concept should be able to be made by anyone, anywhere with access to common tools such as in maker spaces and fab labs. The material and machine choices therefore do not differ between final user concept and functional prototype.
3D printing was chosen from the outset as the joining system required tight tolerances for both fitting components and hardware together in a manner that was structurally sound. As such the prepared 3D printing files could be more complex as the printer would handle their fabrication and remove chance of user error for those less skilled with fabrication and making skills.
- For hard surfaces the recommended material of plywood is best fabricated on a CNC mill.
- While a laser cutter is also an option it requires more finishing due to the burnt edges needing sanding.
- The decided on thickness of between 9-12 mm plywood takes considerably longer to cut to size on a laser cutter compared to a CNC mill also.
Material Choice
Wooden Dowels – Pine
Pine wood dowels were chosen primarily due to the accessibility of pine dowels being the most common alongside its cheaper comparative cost to hardwood dowels.
The mechanical properties of pine wood dowels are less than hardwood alternatives; Scots pine is the most commercially used pine in Europe and the UK and has an elastic modulus of 1.46 x 10^6 (Meier, 2008), however due to the considered diameter of the dowels used being 25mm the mechanical properties of pine will withstand abuse load cases for household furniture.
From a sustainability perspective it is recommended that wood is sourced from FSC certified suppliers who ensure that timbers are sustainably forested to ensure ecological and environmental damage is minimized.
Softwood also grows at a much faster rate than hardwoods meaning that cut trees are replenished and the impact of logging felt for a shorter time than felling of very old hardwood trees. (Roadmap to Change, n.d.)
Effective management of softwood forests for timber is actually shown to be an effective form of carbon sequestering that offsets the emissions caused by the industry. (Cannell, 1999)
- Meier, E., 2008. Scots Pine – Lumber Identification (Softwood). [online] The Wood Database. Available at: <https://www.wood-database.com/scots-pine/>.
- Fsc.org. n.d. Roadmap To Change. [online] Available at: <https://fsc.org/en/impact/roadmap-to-change>.
- Cannell, M., 1999. Growing trees to sequester carbon in the UK: answers to some common questions. Forestry, 72(3), pp.237-247.
Hard Surfaces – Plywood
- The Upstyle Wood Guide. n.d. Sustainability And MDF. [online] Available at: <http://www.woodguide.org/guide/mdf/>.
- The Upstyle Wood Guide. n.d. Sustainability And Plywood. [online] Available at: <http://www.woodguide.org/guide/plywood/>.
3D Printing Filament
- n.d. Comparison Of Typical 3D Printing Materials. [ebook] Boston: International Genetically Engineered Machine, pp.1-7. Available at: <http://2015.igem.org/wiki/images/2/24/CamJIC-Specs-Strength.pdf>.
- 3D Hubs. 2020. PLA Vs. ABS: What’s The Difference?. [online] Available at: <https://www.3dhubs.com/knowledge-base/pla-vs-abs-whats-difference/#introduction>.
- Carlota, V., n.d. Is PLA Filament Actually Biodegradable?. [online] 3D Natives. Available at: <https://www.3dnatives.com/en/pla-filament-230720194/>.
In the comparison of ABS vs PLA, ABS is the one with superior mechanical properties to PLA preforming with much more stability to a higher temperature range. (Comparison of typical 3D printing materials, n.d)
Considering that the goal of the project was to create furniture that had a lower environmental impact than that of current fast furniture solutions. PLA is the more appropriate for achieving this as its end of life impact is less than that of ABS if both were to end up in a landfill.
During development PLA was used as the material assigned during simulations so that even with the less advantageous mechanical properties, parts would still meet the requirements to be safely loaded with either material. This was done as due to users controlling fabrication and material choice the weaker material still needed to be safe to use for the product; in case of it is chosen by users regardless.
Whilst not easily biodegradable unless within factory conditions (Carlota, n.d), an increase in both home and third-party companies recycling PLA filament provides a more environmentally conscious alternative to finite petrochemical filaments, such as ABS.
Optimizing Print Material Use
A comparison of one of IKEA’s largest wardrobes to a matched alternative using the Drift furniture system highlighted that assuming solid infill for all pieces was the strongest option; consumption of up to 14 reels of PLA filament was needed for all the required components. Making the system both economically nonviable as it would be more expensive, and also very wasteful.
Infill and Shells
Research into optimizing mechanical properties of FDM printed parts showed that mechanical properties of stiffness, tensile strength and yield strength are actually shown to be higher when alternatives to solid infill are used.
- Diminishing returns for material usage are found for infill greater than 60%
- Higher shells with lower infill ratios are both material efficient and have higher strength and stiffness.
More practical tests done by CNC kitchen highlight that most of the stresses and strains experienced are towards the outer walls of a print and therefore higher shells is the contributing factor to the majority of a prints strength.
- Page, C., Kreuzer, S., Ansari, F., Eason, D., Hamed, E. and Watson, H., 2017. Optimizing 3D printed components: a methodological approach to assessing print parameters on tensile properties. In Proceedings of ANTEC (pp. 82-88).
- CNC Kitchen, 2018. INFILL Pattern And SHELLS – How To Get The Maximum STRENGTH Out Of Your 3D Prints?. Available at: <https://www.youtube.com/watch?v=AmEaNAwFSfI>.
Layer Height and Direction
Research into layer height showed that strength of parts is much stronger when parts are printed with layer perpendicular to the direction of the force to prevent de-lamination of the layers from each other.
Layer height itself was shown to provide better mechanical properties when it was less than half of the total nozzle diameter.
Both of these in combination help to reduce anisotropy of properties caused by FDM printing.
- Kuznetsov, V., Solonin, A., Urzhumtsev, O., Schilling, R. and Tavitov, A., 2018. Strength of PLA Components Fabricated with Fused Deposition Technology Using a Desktop 3D Printer as a Function of Geometrical Parameters of the Process. Polymers, 10(3), p.313.
Changes to Printed Parts
- Infill ratio was reduced to 30%
- Shells (outer perimeters) increased to 4
- Layer heights of 0.15 to 0.2 mm (assuming a standard 0.35 to 0.4 mm nozzle)
- Connector parts likely to experience vertical loads whilst holding dowels horizontally were recommended to be printed laying flat over vertically in the product specification document.
A combination of these changes would allow for parts to maintain their strength to meet the design specification whilst also reducing material used from 14 reels of filament down to 5.
In general a material reduction of 64%
