Category: Do It Yourself

Prototyping Toolkit for Prosthetic Arm Extensions

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Prototyping Toolkit for Prosthetic Arm Extensions is designed for individuals with upper extremity amputations. The goal is to give users the ability to test and prototype prosthetic arm extensions and search for the right dimensions and positioning. All of the toolkit's components were designed to be 3D printed, laser cut or are off-the-shelf available.

The Toolkit is can be used in a rehabilitation environment, as it allows the occupational therapists, patients, and others to co-create custom-made DIY assistive technology, perfectly fitting the needs of one patient. Once the person knows which position, dimensioning, and adjustability is comfortable, the tool can be reproduced in steel or other more durable materials. The Toolkit mainly functions as a prototyping and testing step before an assistive tool is immediately made.

Technical Specifications: 

Step 1: Collecting the needed off-the-shelf available components. To assemble the toolkit, these components will be needed:

  • M5x30 millimeter bolts
  • M5 wing nuts
  • 4 millimeters diameter axis with a length of 13 millimeter (you can use a nail, etc.)
  • Eventually zip ties, ropes or other connection tool

Step 2: 3D printing the different components. The 3D printed components was designed to be printed on every machine, even the cheaper desktop machinery. If you don't have your own 3D printer, you can take advantage of the growing number of fabrication laboratories, 3D hubs and 3D printing services. The author used 'Polymax PLA' ( on an Ultimaker 2.0 to print the parts. If you decide to print your own version at home or produce your toolkit in a fabrication laboratory, I would recommend this filament. Also, I would recommend a minimum infill percentage of 50% and a layer thickness of 1,2 millimeters. If you let the parts be printed by a hub or service, ask them for a durable and tough material that fits your budget. All files can be downloaded on Thingiverse:

Step 3: Laser cutting the extension pieces and rings. To adjust the length of the Prosthetic Arm Extensions, is a laser cut cross designed to be used as an extension piece. Also, a set of rings can be laser cut to let the joints move freely instead of being fixed in one position. For the sheet material to be laser cut, the author recommends ABS or PA with a thickness of 3 millimeters. The strength is mainly in the structure so it should work with other materials too. Though, plexi-glass for instance will be too brittle and wood won't be durable when used in water. If no laser cutter is available, the laser cut crosses can be replaced by off-the-shelf available, square profiles of 15 x 15 millimeters. These files were also added on Thingiverse:

Step 4: Assemble the toolkit and attach tools. The modular toolkit allows you to assemble the components in many ways. Please reference the picture for guidance on how to assemble the kit. 

Step 5: Connect the toolkit with the prosthetic work-arm. The toolkit can be attached to a prosthetic work-arm or a myo-electric prosthetic arm, using the pin connection shown above. For strength reasons, the author recommends to use an off-the-shelf available axis with a diameter of 4 millimeters and cut it to a length of 13 millimeters instead of 3D printing this axis. The files on Thingiverse were designed this way.

Step 6: Test, learn, or make your own tool connections. In a rehabilitation context, many useful tests can be done with this Toolkit. Patients, occupational therapists and other thirds can explore and test very quickly what is useful and good for one specific case. Feel free to test your own applications and make your own tool connections if needed. On Thingiverse, different connections are already shared, as a connection for zip ties and a screw clamp.

Step 7: Optional: Reproduction of the outcome out of steel. Once a comfortable and functional outcome is found with this toolkit, the assistive tool can be reproduced in steel or in another durable material if necessary. Of course, for some applications the 3D printed model will suffice. It can be useful to use these off-the-shelf available serrated rings:



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Prototyping Toolkit for Prosthetic Arm Extensions