Open source

Michigan Tech researchers invent open-source grinding machine for compression screw 3D printing

Perennial 3D printing innovator and Professor at Michigan Technological University (MTU) Joshua Pearce, has teamed up with MTU colleague Jacob Franz, to create an open-source grinding machine for compression screw manufacturing. 

Dr Pearce, who has consistently championed the advancement of open-source 3D printing, led the project, which yielded a low-cost, easily replicable open-source machine. Reportedly costing less than $155 to build, the device proved capable of replicating commercial screws, while providing greater flexibility for users to make their own. The grinder could enable the manufacturing toolchain to become more self-sufficient, while reducing the costs and waste currently associated with prosumer 3D printing. 

“The grinding device was able to successfully manufacture custom extrusion screws, which radically reduced the cost of one of the core components of desktop-sized open-source FPF 3D printers,” stated the researchers. “This ability will provide the maker community with access to low-cost screws, thereby benefiting the circular economy based on distributed recycling and additive manufacturing.” 

Franz and Pearce's invention, the open-source grinding machine (pictured). Image via MDPI.
Franz and Pearce’s invention, the open-source grinding machine (pictured). Photo via MDPI.

The open-source inspiration for the grinding machine 

Inspired by innovations in the open-source software movement, the research duo claim that something similar is happening within the hardware community, albeit 15 years behind. This “open-hardware” movement continues to be driven forwards by platform technologies such as the Arduino electronics platform and the RepRap projectDesigned to create 3D printers that are able to print their own components, the RepRap project radically reduced the cost of entry to 3D printing. Not only did this create millions of free and open-source 3D-printable designs, but arguably the prosumer manufacturer as well. 

RepRap printers are now used in all kinds of applications ranging from toys to end-use scientific tools, and 3D printing companies understand the challenges posed by this form of distributive manufacturing. Users are now able to cut out the need for distribution altogether and produce parts at a reduced price. Nonetheless, these savings are based upon Fused Filament Fabrication (FFF) 3D printing, and commercial filament is generally sold for around $20 per kg. Virgin plastic pellets, meanwhile, only cost around $1–5  per kg, and the researchers began to consider how they could reduce prosumer printing’s reliance on filaments, in order to lower its costs. 

Previous research has shown that it’s both technically viable and less expensive to use distributed manufacturing in order to fabricate, by using an open-source waste plastic extruder or “recyclebot.” Moreover, because the energy and pollution caused by transportation between processing steps would be eliminated, the environmental benefits of both distributed recycling and manufacturing are clear. Unfortunately, while many widely-used plastics can be recycled for use with FFF, the recyclebot’s melt solidification stage degrades the properties of the resultant object, and limits its recyclability. 

Grinding post-consumer waste with an open-source waste plastic granulator, on the other hand, would remove the need to extrude filament entirely, by making flakes or particles and directly printing from these. After the initial product has been created, Fused Particle fabrication (FPF) systems are able to regrind or reuse shreds of recycled plastic, thus reducing waste. Many FPF 3D printers are currently in development such as the Gigabot X open-source industrial system, but these are often more expensive than their FFF counterparts. 

This is largely due to the expense of the precision-machined compression screw, a part that is also used within commercial recyclebots. In addition, while early testing of desktop FPF printers has been promising, their ability to handle larger pellets is restricted because of the commercially-available small-scale compression screw designs in use. As a result, the researchers have developed an open-source alternative grinding machine, which they hope will allow FPF 3D printing to reach its full potential.

The researchers' screw manufacturing device has been built on a plywood base for cost and functionality purposes. Photo via MDPI.
The researchers’ screw manufacturing device has been built on a plywood base for cost and functionality purposes. Photo via MDPI.

Creating the open-source grinder

In the spirit of the RepRap methodology, many of the components used to create the grinding machine, can be fabricated using FPF. Inspired by lathe machines currently used in wood and metalworking applications, the system’s components were chosen for both their functionality and cost efficiency value. 

While the frame of the machine is currently manufactured out of plywood for its low cost and ability and conformability, all of its 3D-printed components can be printed using polylactic acids (PLA) and thermoplastic elastomers (TPE). In order to produce their prototype, the MTU team 3D printed its components using a Lulzbot Taz 6 system. While a CNC wood router was used to produce the plywood parts, the team acknowledged that a wood working saw or drill press could also be used as makeshift alternatives in the absence of a CNC router. 

Once the device had been assembled, and its 3D printed parts installed, the researchers carried out machine characterization and demonstration tests on their invention. The total cost of the machine was less than $155 excluding the cutting tool used for machining the compression screws, and it testing showed it was capable of cutting a screw section up to 110 mm in length. Several example screws were manufactured to showcase the system’s adjustable parameters. Not only did these match the diameter of the purchased screw, but they also featured improved channel depths to allow larger plastic pellets to enter the extruder. 

Ultimately, while the researchers’ grinding machine proved capable of machining compression screws in a way that lent itself more readily to FPF printing; it did exhibit some flaws. For example, the machine currently relies on mechanical gearing to determine the screw parameters, which can be time-consuming. Nonetheless, the system was presented as fully-functional, and given the open-source nature of the machine’s design, the MTU team is confident that makers and prosumers will improve upon the grinder’s capabilities in the future.

“The device is more than capable of replicating commercial screws as well as providing makers with a much greater flexibility to make custom screws,” stated the researchers. “This ability has added to the DRAM toolchain by enabling makerspaces, fab labs, companies and universities to fabricate compression screws rapidly for approximately the cost of the bar stock, which assists the goals of the circular economy based on distributed recycling and additive manufacturing,” 

For prosumers and makers wanting to recreate the researchers’ 3D printed design, the open-source paper titled “Open-Source Grinding Machine for Compression Screw Manufacturing” and assembly instructions are available here.

The screw purchased by the researchers (pictured), featured a channel depth that was significantly smaller than the diameter of the pellets. Photo via MDPI.
The screw purchased by the researchers (pictured), featured a channel depth that was significantly smaller than the diameter of the pellets. Photo via MDPI.

Joshua Pearce’s additive inventions

Professor Pearce has been an advocate of the benefits of open-source 3D printing for some time, and reportedly even gets his classes to create RepRap 3D printers. As a result, his work has often led to the invention of products that enhance upon or create new open-source applications within AM. 

For example, in July 2017, Pearce led a study that aimed to assess the potential savings of 3D printing toys and games at home. Using an FDM 3D printer with a number of different filaments, the researchers found that costs could be reduced by more than 75 percent. In another study, Pearce identified Casio watch straps, ice cube trays, and phone cases as products that could potentially be 3D printed cheaper than those commercially available. Cost savings achieved by the project ranged from 75 to 92 percent. 

Similarly, Pearce worked on a study in January 2018, which invented a method of 3D printing slot die components, which could only previously be machined from stainless steel. The new methodology reduced the price of an average slot die cast part from nearly $4,000 to 25 cents. 

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Featured image shows Franz and Pearce’s invention, the open-source grinding machine. Photo via MDPI.