# Evaluating 3D Printers Using Data Envelopment Analysis
## 3 Data Collection and Implementation  
There is currently a plethora of 3D printers based on FDM/FFF technology that are available on the market. A rough estimation of available systems and machine vendors according to several specialized and general industrial web sites and sources (directin-dustry.com, 3 Dhubs.com, 3 dprintingindustry.com, 3 ders.org, all3 dp.com; all web sitesaccessed on various dates between March 2018-October 2019) shows that well above 200 models and systems from more than 40 vendors are currently offered worldwide. The corresponding prices for the great majority of systems falls mostly in the low to medium range (a few hundred to a few thousand dollars) but there are also high-end industrial scale systems available priced at several tens of thousands dollars. FDM/FFF printers can be supplied either fully assembled or as Do-It-Yourself (DIY) kits that are assembled by the user. In the case of DIY kits, the buyer will usually take into account the perceived difficulty of assembly and whether sufficient instructions are provided by the manufacturer; both factors that depend on the level of user's experience with 3D printers and are, therefore, quite subjective. In order, therefore, to avoid this non-objective parameter, printers provided as assembly kits were excluded from the analysis. Based on the results of the preliminary analysis, a homogeneous initial population of assembled FDM/FFF printers, i.e., printers based on the thermoplastic material extrusion technology, offered at a price below USD 5000, has been constructed (273 printers). Low cost 3D printers based on other technologies, such as SLA or DLP, were excluded from the analysis because they are quite different in terms of materials and technical features. The corresponding final list contains several models from various companies including, but not limited to, the following (in alphabetical order): Anet, Craftunique, Creality, Dremel, Flashforge, Leapfrog, Lulzbot, Makerbot, Makergear, Monoprice, Prusa3D, Qidi, Raise3D, Ultimaker, and Wanhao. The majority of these printers are developed and offered according to the \"low-cost online business model\", whose main aim is to provide quality printers at low cost, with emphasis being placed at speed, ease-of-use, and durability [52]. In terms of materials, all identified printers can process standard PLA and ABS filaments. Depending on the configuration and capabilities of each printer, several other thermoplastic materials can be used. Some of the most commonly used thermoplastic materials for FDM/FFF printers and their basic properties and price range are summarized in Table 1. Printers equipped with two or more nozzles are considered capable of employing a secondary material, such as water-soluble PVA, for sacrificial support structures. Identified printers do not incorporate a heated chamber, since this a patent-protected feature of Stratasys and would, therefore, significantly limit the initial population. They can, however, incorporate a heated platform or an enclosed chamber. Other non-standard features, such as a moving/conveyer build surface or a rotating build table for continuous printing and automatic part removal, were not considered too, for the same reason. In terms of software, the corresponding printers are usually accompanied by specially-developed slicing software but can, also, be programmed employing popular, freely available slicers such as Cura (ultimaker.com/software/ultimaker-cura, accessed on 26 April 2021), Prussicer (www.prusa3d.com/prussalicer/, accessed on 26 April 2021), Craftware (craftbot.com/software, accessed on 26 April 2021) and/or Repetier (www.repetier.com/, accessed on 26 April 2021). The above software tools allow the user to appropriately define basic printer properties and parameters (workspace shape and dimensions, number of nozzles, filament diameter, etc.) to fit the specific printer. They offer, also, basic slicing features such as the definition of build parameters (build orientation, layer thickness,