I have always been a bit OCD when it comes to door handles. When possible I try to avoid contacts with things that other people touch. If there is no way I can avoid it, as soon as I can, I wash my hands because I am pretty bad at not touching my face…
But now with these strange times upon us, more than ever, I try to limit these contacts. I came up with a tool design that works pretty good and I wanted to share it as my modest participation to COVID-19, and more generally non-hygienic, contacts mitigation.
There is probably a ton of similar devices here and there but this one is mine and I specifically designed it to work for my daily needs: access to my apartment complex and to my work. Maybe it will work for you as is and if it not, feel free to modify it!
But first, a short disclaimer:
I am not a medical doctor or a biologist specialized in viruses so I have no idea if this thing is protecting me or not. Using it could totally make things worst and the viruses and bacteria could strive inside it. I have no idea. Whenever you can, you should wash your hands for the duration the authorities are advising you to do so and clean the device the same way.
I designed this device with my engineering skills and it makes me feel better to use it instead of touching stuff with my bear hands.
My goal was to design something that can be 3D printed and that would fit in a pocket or a purse. I went through several iterations to improve the design.
The main objective was to have the surfaces in contact with potential contamination sources to be stowed away when not in use. This not very complicated to achieve but it would most likely require a lot of small parts and multiple motions which would defeat the second objective to have something that everyone can make as long as they have access to a 3D printer. Planning to carry it in my pocket it would also have to be something rounded to be comfortable when walking and sitting.
After these considerations, comes the function itself. The objective was to be able to handle multiple kind of handles in my building. These are the kind of door handles that the device would have to be compatible with:
- The round handle
- The flat handle
- The bent handle
The Push Bars
The device should also be able to deal with this type of doors. To actuate, it requires a stable and relatively large surface of contact so the force per square millimeters is not too high for a 3D printed device.
If you push the bar with one finger it is quite hard, but with the palm it’s a piece of cake.
The Elevator Switches
Door handles are one thing, but I also need to be able to operate the elevator. So on top of the C shape, I had to find a way to be able to push buttons:
I looked at my hand shape when I actuate these handles and it is always the same: my palm forms a “C” either to pull or twist an handle. This is how I came up with the basic “C shape” design and started to iterate around it.
That shape is round so compatible with the comfort objective. It is a simple shape than can be easily 3D printed which meets the second objective. And finally if I have two “C shapes” that slides into each other, when it forms a “O shape” the exposed surfaces are inside the device which meets the primary objective.
- The round handle was the easiest to figure out and it is the one that dictated the diameter of the “C Shape”:
I wish it was slightly smaller to make the C Handler a bit smaller, but the diameter is about 1″ in this building.
- The flat handle worked perfectly with the “C Shape”:
- The worst of all, the infamous bent handle:
The push bar forced me to iterate a bit on the design. At first the Contactor was recessed inside the Sleeve but I had to have it stick out so only the faces protected when the C Handler is closed were exposed during actuation.
Like the palm idea for the shape, I naturally came up with the Bar design to mimic the finger pushing a button.
After few iterations I added some features to further improve the design.
Instead of using a screw with a washer, I found a screw with a large knurled head to ease the manipulation. A stainless steel thumb screw and nut should be use to prevent rusting because of frequent cleaning.
The dips on the sleeve helps to reduce the necessary torque on the knob/screw to prevent sliding when pushing or inadvertent opening.
These dips also provide a tactile feedback to know that your fingers are close to the edge and might touch the Contactor.
The flats on the edge of the Sleeve reinforce this feedback and also slightly put the fingers further apart from the Contactor while not increasing to much the overall dimensions. They also helps to thicken the material on the weak points of the Sleeve.
The Bar can be pulled out without having to open the “C” to quickly push a button or actuate a toggle switch.
If you are skilled, you can also open trash cans without having the external faces of the C Handler touch the trash.
There are some weak points on the Sleeve and the Bar that don’t really matter during usage but that can break during cleaning:
- For the Sleeve, because of the slot that goes almost all around, there are only two small connections between the two sides.
- For the Bar, the wall is very thin around the Nut.
Loctite reinforcement around the Nut is a good solution to avoid breakage during cleaning but make sure no glue gets into the threads…
Loctite can also be a good repair solution if you happen to break the Sleeve in half…
The inside of the Contactor where the Bar slides is not easy to clean.
The Thumb Screw can be unscrewed too much and fall. Unfortunately, with the overall thickness, having a captive screw is not practical.
It is hard to screw/unscrew the Thumb Screw while holding the device with one hand. Unfortunately to be able to handle 1″ round handles, it makes the whole device quite big. Feel free to scale it down if you don’t have such doors.
It is not compatible with round door knobs. There are none in my building so I have not tried to design something around it but the tricky part is that there is no surface to apply the torque, you need friction.
Manufacturing and procurement
There are very few components to make a C Handler. Three components to print and two standard hardware components.
Bill Of Materials
- 1x Sleeve
- 1x Contactor
- 1x Bar
- 1x M3 Thumb Screw
- 1x M3 Nut
I used some standard black ABS with a relatively low end FDM 3D printer. I set it up to the max resolution and smallest layer thickness.
Because of the rounded shape, I printed the Contactor vertically to have the smoother surface finish and the layers in the direction of the force. Also it allows to have no support on the inside of the Bar channel which would be tricky to remove.
I printed the Sleeve at 45° to minimize the support area, the printer program determined the best orientation to achieve that. Also I believe this way the layers are bigger and thus stronger where the weak spots are located.
The Bar should be printed on the side so there is no support material in the Nut’s pocket.
The two components to purchase are the Thumb Screw and the Nut. I chose them to be Stainless Steel for corrosion resistance and metric because it is an international standard. I might be biased being an European but working in the U.S., I have to use the imperial system daily and it is definitely not as seamless as the metric system.
The Thumb Screw
The Thumb Screw can be replaced by the combination of an M3 Large Washer – ISO 7093 and an M3 X 8 Socket Head Cap Screw – ISO 4762. Depending of the manufacturer these have sometime a knurled head which would be ideal in that case.
If you want to go the Thumb Screw route, you can use McMaster 96016A552 in the color of your choice.
A standard M3 Hex Nut – ISO 4032 will do the job. If you are getting it from McMaster along with the Thumb Screw, you can use 91828A211.
The assembly is very simple. Slide the Nut inside the Bar, slide the bar into the Contactor. Then rotate the Contactor while putting it inside the Sleeve. Insert the Thumb Screw trough the Sleeve’s slot into the Bar’s Nut and tighten it.
Washing daily the C Handler with water and dish soap is probably a good start and something more aggressive from times to times. Again, I am not a biologist so I don’t know what is best to kill virus and bacteria.
Every few days washing it disassembled is probably a good idea to reach locations that are not exposed when assembled. I suggest to use a tube cleaning brush.
- First public release