Digital Commons @ Michigan Tech Digital Commons @ Michigan Tech The economics of classroom 3-d printing of open-source digital The economics of classroom 3-d printing of open-source digital designs of learning aids designs of learning aids

: While schools struggle ﬁnancially, capital for purchasing physical learning aids is often cut. To determine if costs could be reduced for learning aids, this study analyzed classroom-based distributed digital manufacturing using 3-D printing of open-source learning aid designs. Learning aid designs are analyzed in detail for their economic viability considering printing and assembly costs with purchased components and compared to equivalent or inferior commercial products available on Amazon. The results show current open-source 3-D printers are capable of manufacturing useful learning aids and that doing so provides high economic savings in the classroom. Overall, the average learning aid would save teachers 86% when fabricating it themselves. The results show that the average design evaluated was downloaded over 1,500 times and the average savings per year per open-source learning aid design was USD 11,822. To date, the 38 learning aid designs evaluated in this study saved over USD 45,000 each and the total of all of them saved the international educational community over USD 1.7 million. It is clear that investing in the development of open-source learning aids for students provides a return on investment (ROI) for investors hoping to improve education, on average, of more than 100%. J.M.P.; investigation, N.G. resources, J.M.P; data curation, N.G. writing—original preparation, N.G. writing—review N.G. J.M.P.; N.G.


Introduction
Schools throughout the world in both developing countries [1] and even in wealthy countries like the U.S. have been chronically underfunded [2][3][4]. This presents challenges to teachers in optimizing the education of their pupils at every level. Schools under financial stress are trying to find ways to deliver high-quality education for the lowest possible cost [5]. Capital costs in particular are often the first to be cut [6], which largely limit teachers' abilities to afford hardware-based learning aids [7]. These teaching and learning aids tend to be expensive and only available to wealthy school districts in the developed world [8]. Engaging teaching and learning aids were found to be particularly effective for special education students [8], such as for visually impaired people, for whom underfunding is widespread.
A rapidly expanding means to reduce prices for consumer goods is distributed manufacturing with digital technologies such as 3-D printers [9][10][11]. 3-D printers are already being increasingly used for industrial additive manufacturing [12], but they can also be used for distributed manufacturing by where all costs are in U.S. dollars and v is the cost of the "vitamins", or any extra materials involved in making the educational aid, m is the mass of the printed part in grams, f is the filament cost per kilogram and e is the electricity cost per g printed. The electricity cost used the average of energy use per g found for the Table 1 prints multiplied by the average U.S. energy cost (USD/kWh), which was taken as the U.S. Energy Information Administration average commercial rate of USD 0.1057/kWh. It should be noted that the relative impact on the total cost of printed objects due to electricity is minimal [23] so the higher electric prices in some regions or school districts would not impact the outcome.

Educational Aid Description Subject Source
Colorful Clock Clock for teacher's aid Math (time) [65] Brain Model A printed model of the human brain Biology [66] Pythagorean's Theorem Visual representation of the Pythagorean theorem with triangles Math [67] Spinal Cord Model A model of the spinal cord with each section of vertebrae color coded Biology [68] Combustion Engine Model A moveable combustion engine Design and Technology [69] The commercial proprietary purchase cost is dependent on the Amazon equivalent product. The marginal savings (S) for each educational aid is determined by: Designs 2020, 4, 50

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where C is the purchase cost of the educational aid without shipping, as all products assumed Amazon Prime membership so the shipping cost of the filament as well as the products could be ignored. The marginal percent change (P) is determined by: The total global savings per year, Gt, for the selected aids was determined by: where t is the number of years a design has been available. The total global savings is thus given by tG t .

Results
The prototypical examples from Table 1 were all successfully printed on the open-source 3-D printer and are shown in . Figure 1 shows a brain model that can be used to show students the various lobes and sulci of the brain. This can be particularly useful in an anatomy or biology class. The brain is small and durable with a platform, so it can stand up on students' desks, as well as being something hand-held that can be passed around class for the children to play with and touch. The Pythagorean theorem learning aid is shown in Figure 2. This is a mathematical visual aid for students who may have a difficult time comprehending how to use this theorem. A teacher would use this when describing a problem that involves finding the hypotenuse of a right triangle. This can be used in any math or math-related class (e.g., basic engineering design) in middle and high school. A combustion engine is shown in Figure 3. This is an interactive model for students in middle school and high school to use. This model can be used in various shop classes and in introductory engineering, physics and automotive classes. It gives a visual representation of what parts interact within a combustion engine versus reading in a book about what it might look like. The clock, shown in Figure 4, is printed with a variety of colors to show that it can be used to help students learn to tell time. The numbers on the clock are large so that students can easily read them, even if they are further away from where the clock may be placed or use glasses to see. This type of learning aid can be used in elementary and middle schools. Finally, Figure 5 shows a spinal cord. This model is excellent in any physiology or biology class. Each segment of the spine is broken up by color and can be removed from the stem for students to hold. The vertebrae can be individually counted and the model provides an excellent resource for students who learn by using their hands. These aids are generally for students who may need help visualizing what is going on and prefer to actually touch things versus reading something from a textbook and looking at photos. These properties are also particularly effective for special education for visually impaired people. 3-D printed objects like the spinal cord possess haptic and tactile features that can be extremely important for educators teaching the blind. The total global savings per year, Gt, for the selected aids was determined by: where t is the number of years a design has been available. The total global savings is thus given by tGt.

Results
The prototypical examples from Table 1 were all successfully printed on the open-source 3-D printer and are shown in Figures 1-5. Figure 1 shows a brain model that can be used to show students the various lobes and sulci of the brain. This can be particularly useful in an anatomy or biology class. The brain is small and durable with a platform, so it can stand up on students' desks, as well as being something hand-held that can be passed around class for the children to play with and touch. The Pythagorean theorem learning aid is shown in Figure 2. This is a mathematical visual aid for students who may have a difficult time comprehending how to use this theorem. A teacher would use this when describing a problem that involves finding the hypotenuse of a right triangle. This can be used in any math or math-related class (e.g., basic engineering design) in middle and high school. A combustion engine is shown in Figure 3. This is an interactive model for students in middle school and high school to use. This model can be used in various shop classes and in introductory engineering, physics and automotive classes. It gives a visual representation of what parts interact within a combustion engine versus reading in a book about what it might look like. The clock, shown in Figure 4, is printed with a variety of colors to show that it can be used to help students learn to tell time. The numbers on the clock are large so that students can easily read them, even if they are further away from where the clock may be placed or use glasses to see. This type of learning aid can be used in elementary and middle schools. Finally, Figure 5 shows a spinal cord. This model is excellent in any physiology or biology class. Each segment of the spine is broken up by color and can be removed from the stem for students to hold. The vertebrae can be individually counted and the model provides an excellent resource for students who learn by using their hands. These aids are generally for students who may need help visualizing what is going on and prefer to actually touch things versus reading something from a textbook and looking at photos. These properties are also particularly effective for special education for visually impaired people. 3-D printed objects like the spinal cord possess haptic and tactile features that can be extremely important for educators teaching the blind.           Overall, the Cura-estimated mass was found to be highly accurate and a constant factor was not necessary to translate between estimated and measured masses. Based on the energy used and mass of the 3-D printed part measured in Table 1, the cost per kg was found to be USD 21.47 with USD 1.479/kg from electricity and USD 19.99/kg from filament material costs. The 3-D printed product total cost and the savings and saving percentages are shown for the prototypical examples in Figures  1-5 in Table 2. It can be clearly seen in Table 2 that the percent savings for the prototypical learning aids are very high (95%) when the vitamins are minimized, but drop substantially (down to 30% for the clock) when substantial purchased components are needed to complete the assembly of the learning aid. Then, using the value of the USD 21.47/kg determined from the experimental study, the 3-D printing costs were estimated based on the sliced mass for all of the teaching aids and are shown in Table 3. Overall, the Cura-estimated mass was found to be highly accurate and a constant factor was not necessary to translate between estimated and measured masses. Based on the energy used and mass of the 3-D printed part measured in Table 1, the cost per kg was found to be USD 21.47 with USD 1.479/kg from electricity and USD 19.99/kg from filament material costs. The 3-D printed product total cost and the savings and saving percentages are shown for the prototypical examples in Figures 1-5 in Table 2. It can be clearly seen in Table 2 that the percent savings for the prototypical learning aids are very high (95%) when the vitamins are minimized, but drop substantially (down to 30% for the clock) when substantial purchased components are needed to complete the assembly of the learning aid. Then, using the value of the USD 21.47/kg determined from the experimental study, the 3-D printing costs were estimated based on the sliced mass for all of the teaching aids and are shown in Table 3.  As can be seen in Table 3, the same trends are observed as in Table 2. The distributed manufactured learning aids all cost substantially less than those that could be purchased from the largest online retailer in the world. The savings were higher for those products that could be 100% 3-D printed. Combining the data from Tables 2 and 3, the average cost to make a learning aid was USD 3.10 and it replaced on average a USD 29.37 product, providing, on average, a saving of 86%. The standard deviation on the percent savings was 19% and it should be noted that the 100% savings were rounded up from some value greater than 99.5%. For example, the design that would save the most when 3-D printed was the screw, with a 99.92% savings rate. The screw can be printed in various sizes and used for different applications. The design that saved the least to self-manufacture was a pendulum wave machine (only 30.40%), which is used for various physics applications. Overall, it is clear that 3-D printing various educational aids provides high savings in the classroom and in the school in almost any context.
It is clear that educators from around the world are already embracing the use of distributed manufacturing to produce learning aids, as demonstrated in Table 4.  The average learning aid evaluated in this study had been downloaded over 1500 times over an average of 3.42 years since it was open sourced and posted. The average savings per year per learning aid were USD 11,822 and, overall, the 38 learning aids evaluated in this study saved about USD 450,000/year. To date, the average saving per learning aid was thus over USD 45,000 and the aggregate of just 38 learning aids saved the international educational community over USD 1.7 million.

Limitations of the Study
There are several limitations to this study. First, the utility of a given educational aid may vary widely in a given classroom and thus the limited selection of aids evaluated here may not be representative for all classrooms. Future work could address this by evaluating more designs but also doing field work to see how 3-D printers are being used in the classroom-specifically those purchased to fabricate educational aids. Another limitation is that not all schools have the initial capital to invest in a 3-D printer. The model used here retails for USD 2500 and is considered a mid-range fused filament fabrication (FFF)-based 3-D printer. Open-source FFF-based 3-D printers can be purchased for 10 times less, and even less if built in kit form. Previous work has shown that these lower cost 3-D printers would be expected to be capable of printing all of the designs evaluated [23]. The major difference is the lower cost printers tend to have a smaller print bed and, for particularly large prints, the model would need to be divided into several parts and then assembled afterwards with tabs or some form of adhesive. In addition, it should be noted that because some of these lower cost 3-D printers do not have heated beds, the distributed manufacturing costs would be slightly lower. Another limitation of this study is that only one material-PLA-was evaluated. It is the one of the safest and best choices for filament, especially around young children; however, other choices of filament could be more durable (e.g., nylon) or more cost-effective and better for the environment (e.g., recycled materials [70][71][72]), depending on the print. It should also be noted that with the nozzle and filament diameter size, a small amount of error occurs within the print, with the larger nozzles providing faster print times but cannot produce fine detail and vice versa. Another source of errors is when taking the Cura-estimated mass of the material. There could be slight error, as Cura rounds to the nearest gram. This could throw some of the calculations off when determining how much is being saved and how much filament is actually being used. Finally, this class of 3-D printer is not foolproof. If a print fails for any reason (e.g., nozzle clog, lack of bed adhesion, etc.), then filament is wasted. Previous studies estimated this failure rate for new printer users at 20% [23], however, the modern self-bed leveling printers have errors far below this. The error rate will depend on the complexity of the print but can be estimated to be in the single digits when using guaranteed printable designs, as was done in this study. It should be noted, however, that the lowest cost 3-D printers that lack a heated bed can increase the probability of print failures from a lack of bed adhesion due to contraction as the part cools during printing. For some polymers, this can be a substantial problem (e.g., polypropylene should not be printed without a heated bed and best results are found with a heated chamber). For PLA, which was used in this study, printing on an unheated bed does not pose any substantial issues, particularly if a common glue stick is used to lay down a thin film before printing to ensure adhesion.

Limitations of Deployment
One of the primary limitations on the further deployment of 3-D printers in schools in the U.S., to take advantage of the distributed manufacturing of learning aids, is the teachers' lack of control over computers in their classrooms. Often, IT departments have strict rules for what can be downloaded on the teachers' computers. Therefore, having access to the open-source (and free) tool chain (e.g., FreeCAD, OpenSCAD or Blender for design [73]; Cura or Slic3r for slicing [74] and PrintRun or Franklin [75] for printer control) can be non-trivial for teachers to implement in the classroom even if they have the technical competency to download and set up the software on their personal computer at home. One approach to overcome this challenge is to make a library of designs specifically for teachers that are pre-sliced and available for specific printers (e.g., an SD card for education). One open-source 3-D printer manufacturer has already attempted to go down this route in part-Prusa Research is developing their prusaprinters.org website. Prusa users can post the gcode for their designs so that less experienced users can download the gcode and print directly without slicing. This, however, does not then make use of the rest of the open-source 3-D printer community that is not using a Prusa and runs the risk of machine damage. Future work is needed to develop such libraries specifically for educational aids to help teachers and perhaps bundle them with commercial open-source 3-D printers when sold in the education market.

Teacher Training
Teachers will also need to be trained on how to use a 3-D printer [48,49], as well as incorporate it into their classroom. The training process for the teachers can be formal, as in a full university course on additive manufacturing, or a 3-day workshop in which teachers learn how to build, maintain and use an open-source 3-D printer from scratch (i.e., [48]). This level of detail, however, is unnecessary for basic use and maintenance. Creality, an open-source 3-D printer manufacturer, estimates that it takes 30 min of using free online videos for someone already familiar with 3-D printers to get their Ender 3 model (USD 170) up and running, but 2-3 h for a completely inexperienced person [76]. As the cost of low-end 3-D printers has come down, more and more students are being exposed to them at home and could be deputized to help set up a classroom 3-D printer. This relatively low level of depth would only enable a teacher to print out pre-designed teaching aids. This is the assumption used in this study and provides access to thousands of learning aids. In order to go further and be able to modify existing designs that were not made parametric or create completely new designs, however, learning CAD (computer aided design) would be necessary. CAD education ranges from a full university course to a self-paced free tutorial (e.g., EduTech [77] or FreeCAD [78]) that could be accomplished over several intense hours or a more leisurely "learning weekend". Fully mastering any of the open-source CAD packages would normally take several months of practice after learning the basics but, again, this is unnecessary to get started. Finally, with the skills to run the printers, teachers would also need to think about the best way to incorporate them into their own classrooms. So, for example, if students are getting distracted, prints can be run while they are at recess, at lunch or overnight/on the weekend. Future work is also needed to reduce the volume of printers during the printing process. It should also be pointed out here that at many schools and universities, the 3-D printing shops are run by an experienced technician. For example, a library might employee an expert 3-D printing employee to enable teachers with minimal training in CAD and additive manufacturing (AM) to obtain learning aids or the help they need to do it themselves without formal training.

Values and Costs
The benefits of centralized large-scale manufacturing are well established in the literature and historically have included reduced costs due to the economies of scale, from: (i) bulk purchasing of materials, supplies and components through large and long-term contracts; (ii) technological advantages of returns to scale in the production function, such as lower embodied energy during manufacturing of a given product because of scale (e.g., injection molding plastic products); (iii) favorable financing in terms of interest, access to capital and a variety of financial instruments; (iv) centralized marketing and (v) increased specialization of employees and managers [79,80]. These advantages of mass-scale centralized manufacturing have created a general trend towards large-scale manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. As the results of this study show, the centralized paradigm is no longer economically competitive because of the advances in distributed manufacturing technology for some products (e.g., learning aids manufactured from plastic). Although this has been pointed out in the literature for other products as detailed in the introduction, the new and rigorously detailed results shown in this study are still somewhat surprising. Table 5. The costs and values for a teaching aid from the teacher's perspective (a red symbol indicates a disadvantage for the teacher/consumer while a green symbol indicates an advantage).

Mass Manufactured Value
Self-Fabricated Cost

Self-Fabricated Value
Design (e.g., R&D) Designs 2020, 4, x FOR PEER REVIEW 11 of 22 favorable financing in terms of interest, access to capital and a variety of financial instruments; (iv) centralized marketing and (v) increased specialization of employees and managers [79,80]. These advantages of mass-scale centralized manufacturing have created a general trend towards large-scale manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. As the results of this study show, the centralized paradigm is no longer economically competitive because of the advances in distributed manufacturing technology for some products (e.g., learning aids manufactured from plastic). Although this has been pointed out in the literature for other products as detailed in the introduction, the new and rigorously detailed results shown in this study are still somewhat surprising. Table 5. The costs and values for a teaching aid from the teacher's perspective (a red symbol indicates a disadvantage for the teacher/consumer while a green symbol indicates an advantage).

Mass Manufactured Value
Self-Fabricated Cost

Self-Fabricated Value
Design (e.g., R&D) favorable financing in terms of interest, access to capital and a variety of financial instruments; (iv) centralized marketing and (v) increased specialization of employees and managers [79,80]. These advantages of mass-scale centralized manufacturing have created a general trend towards large-scale manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. As the results of this study show, the centralized paradigm is no longer economically competitive because of the advances in distributed manufacturing technology for some products (e.g., learning aids manufactured from plastic). Although this has been pointed out in the literature for other products as detailed in the introduction, the new and rigorously detailed results shown in this study are still somewhat surprising. Table 5. The costs and values for a teaching aid from the teacher's perspective (a red symbol indicates a disadvantage for the teacher/consumer while a green symbol indicates an advantage).

Mass Manufactured Value
Self-Fabricated Cost

Self-Fabricated Value
Design (e.g., R&D) favorable financing in terms of interest, access to capital and a variety of financial instruments; (iv) centralized marketing and (v) increased specialization of employees and managers [79,80]. These advantages of mass-scale centralized manufacturing have created a general trend towards large-scale manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. As the results of this study show, the centralized paradigm is no longer economically competitive because of the advances in distributed manufacturing technology for some products (e.g., learning aids manufactured from plastic). Although this has been pointed out in the literature for other products as detailed in the introduction, the new and rigorously detailed results shown in this study are still somewhat surprising. Table 5. The costs and values for a teaching aid from the teacher's perspective (a red symbol indicates a disadvantage for the teacher/consumer while a green symbol indicates an advantage).

Mass Manufactured Value
Self-Fabricated Cost

Self-Fabricated Value
Design (e.g., R&D) favorable financing in terms of interest, access to capital and a variety of financial instrument centralized marketing and (v) increased specialization of employees and managers [79,80]. T advantages of mass-scale centralized manufacturing have created a general trend towards large manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. A results of this study show, the centralized paradigm is no longer economically competitive be of the advances in distributed manufacturing technology for some products (e.g., learning manufactured from plastic). Although this has been pointed out in the literature for other pro as detailed in the introduction, the new and rigorously detailed results shown in this study ar somewhat surprising. favorable financing in terms of interest, access to capital and a variety of financial instruments; (iv) centralized marketing and (v) increased specialization of employees and managers [79,80]. These advantages of mass-scale centralized manufacturing have created a general trend towards large-scale manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. As the results of this study show, the centralized paradigm is no longer economically competitive because of the advances in distributed manufacturing technology for some products (e.g., learning aids manufactured from plastic). Although this has been pointed out in the literature for other products as detailed in the introduction, the new and rigorously detailed results shown in this study are still somewhat surprising. favorable financing in terms of interest, access to capital and a variety of financial instruments; (iv) centralized marketing and (v) increased specialization of employees and managers [79,80]. These advantages of mass-scale centralized manufacturing have created a general trend towards large-scale manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. As the results of this study show, the centralized paradigm is no longer economically competitive because of the advances in distributed manufacturing technology for some products (e.g., learning aids manufactured from plastic). Although this has been pointed out in the literature for other products as detailed in the introduction, the new and rigorously detailed results shown in this study are still somewhat surprising. favorable financing in terms of interest, access to capital and a variety of financial instruments; (iv) centralized marketing and (v) increased specialization of employees and managers [79,80]. These advantages of mass-scale centralized manufacturing have created a general trend towards large-scale manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. As the results of this study show, the centralized paradigm is no longer economically competitive because of the advances in distributed manufacturing technology for some products (e.g., learning aids manufactured from plastic). Although this has been pointed out in the literature for other products as detailed in the introduction, the new and rigorously detailed results shown in this study are still somewhat surprising. favorable financing in terms of interest, access to capital and a variety of financial instruments; (iv) centralized marketing and (v) increased specialization of employees and managers [79,80]. These advantages of mass-scale centralized manufacturing have created a general trend towards large-scale manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. As the results of this study show, the centralized paradigm is no longer economically competitive because of the advances in distributed manufacturing technology for some products (e.g., learning aids manufactured from plastic). Although this has been pointed out in the literature for other products as detailed in the introduction, the new and rigorously detailed results shown in this study are still somewhat surprising. favorable financing in terms of interest, access to capital and a variety of financial instruments; (iv) centralized marketing and (v) increased specialization of employees and managers [79,80]. These advantages of mass-scale centralized manufacturing have created a general trend towards large-scale manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. As the results of this study show, the centralized paradigm is no longer economically competitive because of the advances in distributed manufacturing technology for some products (e.g., learning aids manufactured from plastic). Although this has been pointed out in the literature for other products as detailed in the introduction, the new and rigorously detailed results shown in this study are still somewhat surprising. favorable financing in terms of interest, access to capital and a variety of financial instrument centralized marketing and (v) increased specialization of employees and managers [79,80]. T advantages of mass-scale centralized manufacturing have created a general trend towards large manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. A results of this study show, the centralized paradigm is no longer economically competitive be of the advances in distributed manufacturing technology for some products (e.g., learning manufactured from plastic). Although this has been pointed out in the literature for other pro as detailed in the introduction, the new and rigorously detailed results shown in this study ar somewhat surprising. favorable financing in terms of interest, access to capital and a variety of financial instruments; (iv) centralized marketing and (v) increased specialization of employees and managers [79,80]. These advantages of mass-scale centralized manufacturing have created a general trend towards large-scale manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. As the results of this study show, the centralized paradigm is no longer economically competitive because of the advances in distributed manufacturing technology for some products (e.g., learning aids manufactured from plastic). Although this has been pointed out in the literature for other products as detailed in the introduction, the new and rigorously detailed results shown in this study are still somewhat surprising. favorable financing in terms of interest, access to capital and a variety of financial instruments; (iv) centralized marketing and (v) increased specialization of employees and managers [79,80]. These advantages of mass-scale centralized manufacturing have created a general trend towards large-scale manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. As the results of this study show, the centralized paradigm is no longer economically competitive because of the advances in distributed manufacturing technology for some products (e.g., learning aids manufactured from plastic). Although this has been pointed out in the literature for other products as detailed in the introduction, the new and rigorously detailed results shown in this study are still somewhat surprising. favorable financing in terms of interest, access to capital and a variety of financial instrumen centralized marketing and (v) increased specialization of employees and managers [79,80]. advantages of mass-scale centralized manufacturing have created a general trend towards larg manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. results of this study show, the centralized paradigm is no longer economically competitive b of the advances in distributed manufacturing technology for some products (e.g., learnin manufactured from plastic). Although this has been pointed out in the literature for other pr as detailed in the introduction, the new and rigorously detailed results shown in this study a somewhat surprising. favorable financing in terms of interest, access to capital and a variety of financial instrument centralized marketing and (v) increased specialization of employees and managers [79,80]. T advantages of mass-scale centralized manufacturing have created a general trend towards large manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. A results of this study show, the centralized paradigm is no longer economically competitive be of the advances in distributed manufacturing technology for some products (e.g., learning manufactured from plastic). Although this has been pointed out in the literature for other pro as detailed in the introduction, the new and rigorously detailed results shown in this study ar somewhat surprising. favorable financing in terms of interest, access to capital and a variety of financial instruments; (iv) centralized marketing and (v) increased specialization of employees and managers [79,80]. These advantages of mass-scale centralized manufacturing have created a general trend towards large-scale manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. As the results of this study show, the centralized paradigm is no longer economically competitive because of the advances in distributed manufacturing technology for some products (e.g., learning aids manufactured from plastic). Although this has been pointed out in the literature for other products as detailed in the introduction, the new and rigorously detailed results shown in this study are still somewhat surprising. favorable financing in terms of interest, access to capital and a variety of financial instruments; (iv) centralized marketing and (v) increased specialization of employees and managers [79,80]. These advantages of mass-scale centralized manufacturing have created a general trend towards large-scale manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. As the results of this study show, the centralized paradigm is no longer economically competitive because of the advances in distributed manufacturing technology for some products (e.g., learning aids manufactured from plastic). Although this has been pointed out in the literature for other products as detailed in the introduction, the new and rigorously detailed results shown in this study are still somewhat surprising.

Mass Manufactured Value
Self-Fabricated Cost

Self-Fabricated Value
Shipping results of this study show, the centralized paradigm is no longer economically competitive because of the advances in distributed manufacturing technology for some products (e.g., learning aids manufactured from plastic). Although this has been pointed out in the literature for other products as detailed in the introduction, the new and rigorously detailed results shown in this study are still somewhat surprising. Critics will point out that this study is equating the costs of production with the costs of retailing and may argue that it is not a fair comparison. From the teacher's perspective, however, the cost to obtain a learning aid is the full cost that matters to their supplies budget and the value is only what they acquire in the classroom. To clarify the economic position and provide some insight into why it is less costly to manufacture a learning aid in the classroom than buy a mass-manufactured product, Table 5 shows the costs and values from the teacher's perspective for (1) the typical massmanufactured proprietary product and (2) the distributed self-fabricated open-source products. Each item making up the cost will then be discussed in turn. In Table 5, the green symbols represent a benefit and the red symbols represent a disadvantage for the consumer (e.g., teacher) and the check NA results of this study show, the centralized paradigm is no longer economically competitive because of the advances in distributed manufacturing technology for some products (e.g., learning aids manufactured from plastic). Although this has been pointed out in the literature for other products as detailed in the introduction, the new and rigorously detailed results shown in this study are still somewhat surprising. Critics will point out that this study is equating the costs of production with the costs of retailing and may argue that it is not a fair comparison. From the teacher's perspective, however, the cost to obtain a learning aid is the full cost that matters to their supplies budget and the value is only what they acquire in the classroom. To clarify the economic position and provide some insight into why it is less costly to manufacture a learning aid in the classroom than buy a mass-manufactured product, Table 5 shows the costs and values from the teacher's perspective for (1) the typical massmanufactured proprietary product and (2) the distributed self-fabricated open-source products. Each item making up the cost will then be discussed in turn. In Table 5, the green symbols represent a benefit and the red symbols represent a disadvantage for the consumer (e.g., teacher) and the check NA Retail centralized marketing and (v) increased specialization of employees and managers [79,80]. These advantages of mass-scale centralized manufacturing have created a general trend towards large-scale manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. As the results of this study show, the centralized paradigm is no longer economically competitive because of the advances in distributed manufacturing technology for some products (e.g., learning aids manufactured from plastic). Although this has been pointed out in the literature for other products as detailed in the introduction, the new and rigorously detailed results shown in this study are still somewhat surprising. Critics will point out that this study is equating the costs of production with the costs of retailing and may argue that it is not a fair comparison. From the teacher's perspective, however, the cost to obtain a learning aid is the full cost that matters to their supplies budget and the value is only what they acquire in the classroom. To clarify the economic position and provide some insight into why it is less costly to manufacture a learning aid in the classroom than buy a mass-manufactured product, Table 5 shows the costs and values from the teacher's perspective for (1) the typical massmanufactured proprietary product and (2) the distributed self-fabricated open-source products. Each item making up the cost will then be discussed in turn. In Table 5, the green symbols represent a benefit and the red symbols represent a disadvantage for the consumer (e.g., teacher) and the check NA centralized marketing and (v) increased specialization of employees and managers [79,80]. These advantages of mass-scale centralized manufacturing have created a general trend towards large-scale manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. As the results of this study show, the centralized paradigm is no longer economically competitive because of the advances in distributed manufacturing technology for some products (e.g., learning aids manufactured from plastic). Although this has been pointed out in the literature for other products as detailed in the introduction, the new and rigorously detailed results shown in this study are still somewhat surprising. Critics will point out that this study is equating the costs of production with the costs of retailing and may argue that it is not a fair comparison. From the teacher's perspective, however, the cost to obtain a learning aid is the full cost that matters to their supplies budget and the value is only what they acquire in the classroom. To clarify the economic position and provide some insight into why it is less costly to manufacture a learning aid in the classroom than buy a mass-manufactured product, Table 5 shows the costs and values from the teacher's perspective for (1) the typical massmanufactured proprietary product and (2) the distributed self-fabricated open-source products. Each item making up the cost will then be discussed in turn. In Table 5, the green symbols represent a benefit and the red symbols represent a disadvantage for the consumer (e.g., teacher) and the check favorable financing in terms of interest, access to capital and a variety of financial instruments; (iv) centralized marketing and (v) increased specialization of employees and managers [79,80]. These advantages of mass-scale centralized manufacturing have created a general trend towards large-scale manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. As the results of this study show, the centralized paradigm is no longer economically competitive because of the advances in distributed manufacturing technology for some products (e.g., learning aids manufactured from plastic). Although this has been pointed out in the literature for other products as detailed in the introduction, the new and rigorously detailed results shown in this study are still somewhat surprising. Critics will point out that this study is equating the costs of production with the costs of retailing and may argue that it is not a fair comparison. From the teacher's perspective, however, the cost to obtain a learning aid is the full cost that matters to their supplies budget and the value is only what they acquire in the classroom. To clarify the economic position and provide some insight into why it is less costly to manufacture a learning aid in the classroom than buy a mass-manufactured product, Table 5 shows the costs and values from the teacher's perspective for (1) the typical massmanufactured proprietary product and (2) the distributed self-fabricated open-source products. Each item making up the cost will then be discussed in turn. In Table 5, the green symbols represent a benefit and the red symbols represent a disadvantage for the consumer (e.g., teacher) and the check NA Designs 2020, 4, x FOR PEER REVIEW 11 of 22 favorable financing in terms of interest, access to capital and a variety of financial instruments; (iv) centralized marketing and (v) increased specialization of employees and managers [79,80]. These advantages of mass-scale centralized manufacturing have created a general trend towards large-scale manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. As the results of this study show, the centralized paradigm is no longer economically competitive because of the advances in distributed manufacturing technology for some products (e.g., learning aids manufactured from plastic). Although this has been pointed out in the literature for other products as detailed in the introduction, the new and rigorously detailed results shown in this study are still somewhat surprising. Critics will point out that this study is equating the costs of production with the costs of retailing and may argue that it is not a fair comparison. From the teacher's perspective, however, the cost to obtain a learning aid is the full cost that matters to their supplies budget and the value is only what they acquire in the classroom. To clarify the economic position and provide some insight into why it is less costly to manufacture a learning aid in the classroom than buy a mass-manufactured product, Table 5 shows the costs and values from the teacher's perspective for (1) the typical massmanufactured proprietary product and (2) the distributed self-fabricated open-source products. Each item making up the cost will then be discussed in turn. In Table 5, the green symbols represent a benefit and the red symbols represent a disadvantage for the consumer (e.g., teacher) and the check favorable financing in terms of interest, access to capital and a variety of financial instruments; (iv) centralized marketing and (v) increased specialization of employees and managers [79,80]. These advantages of mass-scale centralized manufacturing have created a general trend towards large-scale manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. As the results of this study show, the centralized paradigm is no longer economically competitive because of the advances in distributed manufacturing technology for some products (e.g., learning aids manufactured from plastic). Although this has been pointed out in the literature for other products as detailed in the introduction, the new and rigorously detailed results shown in this study are still somewhat surprising. Critics will point out that this study is equating the costs of production with the costs of retailing and may argue that it is not a fair comparison. From the teacher's perspective, however, the cost to obtain a learning aid is the full cost that matters to their supplies budget and the value is only what they acquire in the classroom. To clarify the economic position and provide some insight into why it is less costly to manufacture a learning aid in the classroom than buy a mass-manufactured product, Table 5 shows the costs and values from the teacher's perspective for (1) the typical massmanufactured proprietary product and (2) the distributed self-fabricated open-source products. Each item making up the cost will then be discussed in turn. In Table 5, the green symbols represent a benefit and the red symbols represent a disadvantage for the consumer (e.g., teacher) and the check favorable financing in terms of interest, access to capital and a variety of financial instruments; (iv) centralized marketing and (v) increased specialization of employees and managers [79,80]. These advantages of mass-scale centralized manufacturing have created a general trend towards large-scale manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. As the results of this study show, the centralized paradigm is no longer economically competitive because of the advances in distributed manufacturing technology for some products (e.g., learning aids manufactured from plastic). Although this has been pointed out in the literature for other products as detailed in the introduction, the new and rigorously detailed results shown in this study are still somewhat surprising. Table 5. The costs and values for a teaching aid from the teacher's perspective (a red symbol indicates a disadvantage for the teacher/consumer while a green symbol indicates an advantage).

Mass Manufactured Value
Self-Fabricated Cost

Self-Fabricated Value
Design (e.g., R&D) Critics will point out that this study is equating the costs of production with the costs of retailing and may argue that it is not a fair comparison. From the teacher's perspective, however, the cost to obtain a learning aid is the full cost that matters to their supplies budget and the value is only what they acquire in the classroom. To clarify the economic position and provide some insight into why it is less costly to manufacture a learning aid in the classroom than buy a mass-manufactured product, Table 5 shows the costs and values from the teacher's perspective for (1) the typical massmanufactured proprietary product and (2) the distributed self-fabricated open-source products. Each item making up the cost will then be discussed in turn. In Table 5, the green symbols represent a benefit and the red symbols represent a disadvantage for the consumer (e.g., teacher) and the check favorable financing in terms of interest, access to capital and a variety of financial instruments; (iv) centralized marketing and (v) increased specialization of employees and managers [79,80]. These advantages of mass-scale centralized manufacturing have created a general trend towards large-scale manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. As the results of this study show, the centralized paradigm is no longer economically competitive because of the advances in distributed manufacturing technology for some products (e.g., learning aids manufactured from plastic). Although this has been pointed out in the literature for other products as detailed in the introduction, the new and rigorously detailed results shown in this study are still somewhat surprising. Table 5. The costs and values for a teaching aid from the teacher's perspective (a red symbol indicates a disadvantage for the teacher/consumer while a green symbol indicates an advantage).

Mass Manufactured Value
Self-Fabricated Cost

Self-Fabricated Value
Design (e.g., R&D) Critics will point out that this study is equating the costs of production with the costs of retailing and may argue that it is not a fair comparison. From the teacher's perspective, however, the cost to obtain a learning aid is the full cost that matters to their supplies budget and the value is only what they acquire in the classroom. To clarify the economic position and provide some insight into why it is less costly to manufacture a learning aid in the classroom than buy a mass-manufactured product, Table 5 shows the costs and values from the teacher's perspective for (1) the typical massmanufactured proprietary product and (2) the distributed self-fabricated open-source products. Each item making up the cost will then be discussed in turn. In Table 5, the green symbols represent a benefit and the red symbols represent a disadvantage for the consumer (e.g., teacher) and the check favorable financing in terms of interest, access to capital and a variety of financial instruments; (iv) centralized marketing and (v) increased specialization of employees and managers [79,80]. These advantages of mass-scale centralized manufacturing have created a general trend towards large-scale manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. As the results of this study show, the centralized paradigm is no longer economically competitive because of the advances in distributed manufacturing technology for some products (e.g., learning aids manufactured from plastic). Although this has been pointed out in the literature for other products as detailed in the introduction, the new and rigorously detailed results shown in this study are still somewhat surprising. Table 5. The costs and values for a teaching aid from the teacher's perspective (a red symbol indicates a disadvantage for the teacher/consumer while a green symbol indicates an advantage).

Mass Manufactured Value
Self-Fabricated Cost

Self-Fabricated Value
Design (e.g., R&D) Critics will point out that this study is equating the costs of production with the costs of retailing and may argue that it is not a fair comparison. From the teacher's perspective, however, the cost to obtain a learning aid is the full cost that matters to their supplies budget and the value is only what they acquire in the classroom. To clarify the economic position and provide some insight into why it is less costly to manufacture a learning aid in the classroom than buy a mass-manufactured product, Table 5 shows the costs and values from the teacher's perspective for (1) the typical massmanufactured proprietary product and (2) the distributed self-fabricated open-source products. Each item making up the cost will then be discussed in turn. In Table 5, the green symbols represent a benefit and the red symbols represent a disadvantage for the consumer (e.g., teacher) and the check favorable financing in terms of interest, access to capital and a variety of financial instruments; (iv) centralized marketing and (v) increased specialization of employees and managers [79,80]. These advantages of mass-scale centralized manufacturing have created a general trend towards large-scale manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. As the results of this study show, the centralized paradigm is no longer economically competitive because of the advances in distributed manufacturing technology for some products (e.g., learning aids manufactured from plastic). Although this has been pointed out in the literature for other products as detailed in the introduction, the new and rigorously detailed results shown in this study are still somewhat surprising. Table 5. The costs and values for a teaching aid from the teacher's perspective (a red symbol indicates a disadvantage for the teacher/consumer while a green symbol indicates an advantage).

Mass Manufactured Value
Self-Fabricated Cost

Self-Fabricated Value
Design (e.g., R&D) Critics will point out that this study is equating the costs of production with the costs of retailing and may argue that it is not a fair comparison. From the teacher's perspective, however, the cost to obtain a learning aid is the full cost that matters to their supplies budget and the value is only what they acquire in the classroom. To clarify the economic position and provide some insight into why it is less costly to manufacture a learning aid in the classroom than buy a mass-manufactured product, Table 5 shows the costs and values from the teacher's perspective for (1) the typical massmanufactured proprietary product and (2) the distributed self-fabricated open-source products. Each item making up the cost will then be discussed in turn. In Table 5, the green symbols represent a benefit and the red symbols represent a disadvantage for the consumer (e.g., teacher) and the check favorable financing in terms of interest, access to capital and a variety of financial instruments; (iv) centralized marketing and (v) increased specialization of employees and managers [79,80]. These advantages of mass-scale centralized manufacturing have created a general trend towards large-scale manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. As the results of this study show, the centralized paradigm is no longer economically competitive because of the advances in distributed manufacturing technology for some products (e.g., learning aids manufactured from plastic). Although this has been pointed out in the literature for other products as detailed in the introduction, the new and rigorously detailed results shown in this study are still somewhat surprising. Table 5. The costs and values for a teaching aid from the teacher's perspective (a red symbol indicates a disadvantage for the teacher/consumer while a green symbol indicates an advantage).

Mass Manufactured Value
Self-Fabricated Cost

Self-Fabricated Value
Design (e.g., R&D) Critics will point out that this study is equating the costs of production with the costs of retailing and may argue that it is not a fair comparison. From the teacher's perspective, however, the cost to obtain a learning aid is the full cost that matters to their supplies budget and the value is only what they acquire in the classroom. To clarify the economic position and provide some insight into why it is less costly to manufacture a learning aid in the classroom than buy a mass-manufactured product, Table 5 shows the costs and values from the teacher's perspective for (1) the typical massmanufactured proprietary product and (2) the distributed self-fabricated open-source products. Each item making up the cost will then be discussed in turn. In Table 5, the green symbols represent a benefit and the red symbols represent a disadvantage for the consumer (e.g., teacher) and the check

NA Warranty
Designs 2020, 4, x FOR PEER REVIEW 11 of 22 favorable financing in terms of interest, access to capital and a variety of financial instruments; (iv) centralized marketing and (v) increased specialization of employees and managers [79,80]. These advantages of mass-scale centralized manufacturing have created a general trend towards large-scale manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. As the results of this study show, the centralized paradigm is no longer economically competitive because of the advances in distributed manufacturing technology for some products (e.g., learning aids manufactured from plastic). Although this has been pointed out in the literature for other products as detailed in the introduction, the new and rigorously detailed results shown in this study are still somewhat surprising. Critics will point out that this study is equating the costs of production with the costs of retailing and may argue that it is not a fair comparison. From the teacher's perspective, however, the cost to obtain a learning aid is the full cost that matters to their supplies budget and the value is only what they acquire in the classroom. To clarify the economic position and provide some insight into why it is less costly to manufacture a learning aid in the classroom than buy a mass-manufactured product, Table 5 shows the costs and values from the teacher's perspective for (1) the typical massmanufactured proprietary product and (2) the distributed self-fabricated open-source products. Each item making up the cost will then be discussed in turn. In Table 5, the green symbols represent a benefit and the red symbols represent a disadvantage for the consumer (e.g., teacher) and the check Designs 2020, 4, x FOR PEER REVIEW 11 of 22 favorable financing in terms of interest, access to capital and a variety of financial instruments; (iv) centralized marketing and (v) increased specialization of employees and managers [79,80]. These advantages of mass-scale centralized manufacturing have created a general trend towards large-scale manufacturing in low-labor cost countries, especially for inexpensive plastic products [81,82]. As the results of this study show, the centralized paradigm is no longer economically competitive because of the advances in distributed manufacturing technology for some products (e.g., learning aids manufactured from plastic). Although this has been pointed out in the literature for other products as detailed in the introduction, the new and rigorously detailed results shown in this study are still somewhat surprising. Critics will point out that this study is equating the costs of production with the costs of retailing and may argue that it is not a fair comparison. From the teacher's perspective, however, the cost to obtain a learning aid is the full cost that matters to their supplies budget and the value is only what they acquire in the classroom. To clarify the economic position and provide some insight into why it is less costly to manufacture a learning aid in the classroom than buy a mass-manufactured product, Table 5 shows the costs and values from the teacher's perspective for (1) the typical massmanufactured proprietary product and (2) the distributed self-fabricated open-source products. Each item making up the cost will then be discussed in turn. In Table 5, the green symbols represent a benefit and the red symbols represent a disadvantage for the consumer (e.g., teacher) and the check Critics will point out that this study is equating the costs of production with the costs of retailing and may argue that it is not a fair comparison. From the teacher's perspective, however, the cost to obtain a learning aid is the full cost that matters to their supplies budget and the value is only what they acquire in the classroom. To clarify the economic position and provide some insight into why it is less costly to manufacture a learning aid in the classroom than buy a mass-manufactured product, Table 5 shows the costs and values from the teacher's perspective for (1) the typical massmanufactured proprietary product and (2) the distributed self-fabricated open-source products. Each item making up the cost will then be discussed in turn. In Table 5, the green symbols represent a benefit and the red symbols represent a disadvantage for the consumer (e.g., teacher) and the check Critics will point out that this study is equating the costs of production with the costs of retailing and may argue that it is not a fair comparison. From the teacher's perspective, however, the cost to obtain a learning aid is the full cost that matters to their supplies budget and the value is only what they acquire in the classroom. To clarify the economic position and provide some insight into why it is less costly to manufacture a learning aid in the classroom than buy a mass-manufactured product, Table 5 shows the costs and values from the teacher's perspective for (1) the typical massmanufactured proprietary product and (2) the distributed self-fabricated open-source products. Each item making up the cost will then be discussed in turn. In Table 5, the green symbols represent a benefit and the red symbols represent a disadvantage for the consumer (e.g., teacher) and the check Critics will point out that this study is equating the costs of production with the costs of retailing and may argue that it is not a fair comparison. From the teacher's perspective, however, the cost to obtain a learning aid is the full cost that matters to their supplies budget and the value is only what they acquire in the classroom. To clarify the economic position and provide some insight into why it is less costly to manufacture a learning aid in the classroom than buy a mass-manufactured product, Table 5 shows the costs and values from the teacher's perspective for (1) the typical mass-manufactured proprietary product and (2) the distributed self-fabricated open-source products. Each item making up the cost will then be discussed in turn. In Table 5, the green symbols represent a benefit and the red symbols represent a disadvantage for the consumer (e.g., teacher) and the check marks indicate that the item is present while the X indicates that it is not. Thus, the ideal system would have all green marks (X for costs and checks for values).
As can be seen in Table 5, the self-fabricated open-source approach has nearly all of the advantages seen but considerably fewer disadvantages than the mass-manufactured model. This explains in large part why the results of this study found that distributed manufacturing would result in considerable savings for teachers (consumers).
The cost of the research and development (R&D) in the standard model is borne by the company to create the design that benefits the consumer. In the open-source model, however, this same benefit is gained at no cost because the learning aid is open source and developed by someone else. In addition, considerable costs are shouldered by the traditional company for intellectual property (IP) protection, which has no direct benefit to the consumer for a given product. For example, even companies like Apple, that are known for innovation, spend more on lawyers than engineers [83]. On the other hand, there is no IP cost for the open-source self-fabrication model.
The conventional mass-manufacturing company has a substantial advantage in the cost of materials because of bulk purchasing. Assuming identical materials (i.e., plastic) the self-fabricated cost for the materials will be greater (e.g., USD 20/kg for retail 3-D printing filament vs. USD 1-5/kg for bulk plastic) and the value will be the same. Similarly, to fabricate the product, in both cases, the consumer benefits from the product produced and there is a cost associated with the making. This cost is generally divided into labor, energy and equipment costs. The labor costs for the traditional manufacturer is higher as it is essentially free to self-fabricate a pre-designed product on a 3-D printer.
On the other hand, the energy cost would be expected to be larger for the self-fabricator because of the economy of scale advantage for the mass manufacturer. Similarly, the mass manufacturer, although using larger and more expensive equipment (e.g., an injection molding machine), would produce far more copies, thus the machine cost per product would be expected to be lower for mass manufacturing. 3-D printers and the cost in electricity to operate them is so small [23] that neither of these advantages for mass-manufacturing play a major role in the cost of a product.
Next, there are several costs that must be included in a mass-manufactured product that offer the consumer no advantage, which are unnecessary with the open-source approach, including: packaging, shipping, retail (e.g., store costs, online or brick and mortar), advertising, management, financing and profit for the company. Some of these costs can be quite substantial and others represent a disadvantage for the consumer. First, not only are packaging costs eliminated for self-fabricated products, but the consumer also saves time in unpacking items. Packaging waste and difficulty in opening some products are a source of frustration for consumers [84,85]. Second, shipping costs are not only eliminated (assuming 3-D printing feed stock is on hand because it can be purchased ahead of time) but, in general, the print time for a learning aid will be less than the order/ship time for a mass-manufactured product (e.g., the print times for the products here are in the order of hours, while shipping is normally in the order of days). This, again, saves the consumer time, which is a value. The costs associated with the overhead and profit of retail establishments are also all completely eliminated. This is true of the online retailers that need to pay for servers, programmers, etc., but even more so for brick and mortar stores. It is estimated that the markups for retailers were 10% for Costco, 15% for Amazon, 32% for Walmart and 46% for Target [86]. The costs for advertising and marketing are completely eliminated for the self-fabrication model, while advertising represents a time cost and source of frustration for consumers who attempt to protect their time [87] (e.g., some of the most popular plugins for both Firefox [88] and Chrome Internet browsers [89] are for ad blocking software, which have been downloaded tens of millions of times and have saved consumers enormous amounts of time and money by conserving energy to run their computers to service ads [90]). The management costs to run large corporations have swollen [91,92] even when the company is failing [93] and, again, these are not needed in the distributed model. Similarly, financing and profit only add costs to the mass-manufactured model, while they are not needed in the distributed model.
Finally, the mass manufactured products undergo usability, durability and safety testing that enables companies to provide some form of warranty. This has value for the consumer, which is not captured in the self-fabricated approach. This is the one area that may prevent a given product from providing an equivalent value to a mass-manufactured item. This area is most important for products that are likely to fail due to complexity or have a long lifespan. For the products evaluated here made out of plastic and often lacking moving parts, this is unlikely to be a major concern (e.g., would a teacher rather pay less than one USD for a spirograph set he or she can make in class on his or her 3-D printer or pay over USD 15 to buy one from Amazon even if it comes with a warranty?). Future work is needed to determine the value for the consumer for the explicit or implicit warranties (e.g., Amazon returns) for mass-manufactured products.
Overall, it is clear that although mass manufacturing enjoys advantages in material and energy costs compared to the self-fabrication model, it is not enough to overcome all of the other cost disadvantages, which is why the cost to the consumer (e.g., teacher) was found to be so much lower than the retail cost for the teaching and learning aids investigated here.

Overall Economics and Advanced Applications
Despite both this study's limitations and those of the concept of distributed manufacturing in schools with 3-D printers in general, it is clear that fabricating learning aids in the classroom is economic. Even for the relatively expensive 3-D printer used, printing even 100 aids on average would pay for itself. This could easily be accomplished in the "first 100 days" of class. Further, with each teaching aid, on average, that is 3-D printed, the school saves the cost of an entire roll of filament. These savings are clearly substantial and, as seen from Table 4, the technique appears to be already being used throughout the world by teachers or other educators trying to help their students understand concepts. It is quite remarkable that, on average, a given open-source educational aid is saving well over ten thousand U.S. dollars per year for the educational community. This value uses the assumption that for each download, one item is printed, following [94]. It does not take, in general, USD 10,000 worth of engineering time to produce a learning aid. This thus provides a return on investment (ROI) for investors hoping to improve education, on average, of more than 100% [95]. The ROI is so high that it could be justified even in a single school that uses any substantial number of copies of a learning aid. Particularly if these are for more advanced science classes, like optomechanical systems [96], micropumping [97], bioadhesion [98] or bioreactors [99]. The savings that, on average, are 86% for learning aids would go a long way at a school that makes use of learning aids, but perhaps more importantly, with the costs being accessible, more teachers would be likely to use them and the teaching at a school would be improved. This needs further study and is left for future work.
In addition, 3-D printing enables economic access to the ability for schools to integrate special education students using advanced applications. For example, there are open-source parametric 3-D printable designs for Braille patterns developed in OpenSCAD [100]. This script-based computer-aided design is extremely effective at teaching students both to code and the value of math [48], but in this context, it can be used to have students directly help their blind peers learn. This could be a powerful learning motivation and means to better integrate blind and visually impaired students into classrooms. There are already many ways 3-D printers can be used to help blind and visually impaired students, including tactile maps, illustrations for books, learning games and artwork [101]. Fabricating learning aids and even assistive aids for blind and visually impaired students with 3-D printers can make economic learning aids for art teaching [102], but can also get quite functionally sophisticated. For example, a low-cost, open source ultrasound-based navigational support system in the form of a 3-D printable wearable bracelet has been demonstrated to allow people with vision loss to navigate, orient themselves in their surroundings and avoid obstacles when moving. Similarly, research has already shown the efficacy of 3-D printing to create orally disintegrating printlets (ODPs), suitable for patients with visual impairment, with Braille and Moon patterns on their surface, enabling patients to identify medications when taken out of their original packaging [103]. Students may start printing learning aids and Braille labels for peers, but as they become more technically sophisticated, fabricating ultrasound-based navigational aids from open-source plans or ODPs is possible and no longer economically inaccessible. Future work is needed to look closely at this area on both technical and economic grounds.
3-D printers in the classroom can have other ancillary benefits. The opportunity to print objects now can give students something to look forward to when coming to school [48]. They can become more interested in the STEM field [44,45]. Additionally, students could design their own objects that can be made for classrooms or younger children to help proactive learners. In general, students that are first exposed to 3-D printers love to watch the printer work its magic and make objects. Young students ask questions about the printer, such as "How hot does it get to melt the plastic?" and "How does it know how to print what we want?". Students are curious about the machine itself and would touch the print bed or the filament. 3-D printers (or even using them) could be used as prizes or awards for good student behavior or achievements. Finally, it could lead students who have already graduated to give back to the schools they grew up in following the open-source model [27,28]. This equipment in the classroom gives the school a higher sense of technology. This may ultimately boost educational quality (e.g., ratings), attracting more students (e.g., funding).

Conclusions
This study successfully analyzed the economics of classroom-based 3-D printing of open-source digital designs of learning aids for the classroom itself. The results show current open-source 3-D printers are more than capable of manufacturing useful learning aids. Further, this distributed manufacturing for education will save schools money. The average substitution of a purchase of a learning aid for one that is 3-D printed saves more than the cost of a 1 kg spool of commercial filament. Overall, the average learning aid would save teachers 86% by fabricating it themselves. Even for relatively expensive commercial 3-D printers, a school could save the cost of the investment in the first 100 days of class. It is clear that 3-D printing various educational aids provides high savings in the classroom and in the school in almost any context. This study also provided preliminary evidence that educators from around the world are already embracing the use of distributed manufacturing to produce learning aids. The results show that the average learning aid evaluated in this study was downloaded over 1500 times and presumably printed as many times. The average savings per year per open-source learning aid design was USD 11,822 and, overall, the 38 learning aids evaluated in this study saved about USD 450,000/year. To date, the 38 learning aids evaluated in this study have, on average, produced a saving per learning aid of over USD 45,000 and the total of all of them has saved the international educational community over USD 1.7 million to date. It is clear that investing in the development of open-source learning aids for students provides a return on investment (ROI) for investors hoping to improve education, on average, of more than 100%. Finally, future work is needed to develop libraries of open-source designs specifically for educational aids to help teachers and perhaps bundle them with commercial open-source 3-D printers when sold in the education market.

Aid
Amazon URL Table A2. Cont.