For people with limited hand strength due to injury or arthritis, turning a door knob can be a challenge. Long term solutions include replacing door knobs with door levers or purchasing assistive door levers that can be attached to existing door knobs. However, both options can get expensive if there are many doors that need to be modified.
These options also do not address a temporary situation where a person with limited hand strength is visiting a relative or if someone is hosting a relative with limited hand strength.
This concept utilizes 3D printing to create an inexpensive, portable assistive door handle. Print as many as you need or modify the design for a custom fit (or a custom look).
Step 1: Materials and Equipment
- 3D printer (alternatively, a version could be made on a CNC or ShopBot)
- Pivot Pin (Nut and Bolt, Dowel, etc.)
- Elastic Band (Optional)
Step 2: How It Works
The CAD model shows how the lever acts like a cam to squeeze the door knob (similar to how some oil filter wrenches operate).
- Slide the BLUE Main Body over the door knob. The elastic band keeps it from rotating and falling off (when not being held).
- Rotate the WHITE Handle to create friction to turn the door knob. Since it was designed for this door knob, I was even able to operate it with just one finger.
- Note: The design is symmetric and can be used with the handle facing either right or left.
Step 3: Handle Optimization and 3D Printing
The Handle can be designed and 3D printed as a solid, but in the example shown I printed a version where I added reinforcing ribs. I have attached STL files for both a solid and a ribbed version.
Step 4: Main Body Optimiztion and 3D Printing
The Main Body was designed to be 3D printed vertically with no support material, but I realized that this would result in a potentially weak cross section (due to the way 3D printing creates layers of material), so I chose to print the part flat. This resulted in support material filling in the slot, but as you can see it was easily pulled out.
Step 5: Future Improvements
This design was optimized for a disc-shaped door knob. While it fit other door knob shapes (round, tapered), it did not feel as secure. Can the Main Body be modified to be more universal? Can the clamping action of the cam be improved? Should the Handle be made stronger or more ergonomic?
This might be a good STEM project for students (mechanical design, 3D printing, making devices for people that need them)...