Practical Print: Chair Armrest - Design Edition

One of the things we love about 3D printing is its versatility and practicality, hence one of our favorite segments: Practical Print! And the print we have for you this week is truly practical indeed. In fact, in this Practical Print we’re going to be diving a little deeper into our design, designing from the ground (or arm) up, rapidly prototyping it to meet our needs, and testing it out so that it’s a perfectly snug fit, and we’re bringing you along every step of the way!


So what do you do when the armrest on your chair cracks like ours in the office has?


Well, if you’re a maker, the first thing you probably thought was “I can print a replacement!” But we’re not just going to simply print an exact replica of the armrest that was broken, we’re going to make it even better.


We’re going to be following a tried and true design-build-test methodology to create the best chair armrest for our office. If you’re unfamiliar with this process, here are the basic steps:

  1. Create the model

  2. Build a prototype (3D printing)

  3. Test the design

  4. Repeat steps 2&3 as needed


The Model

To start off our model, we wanted to get a baseline design of the current chair armrest. So, we modeled the existing one so that we could more closely take a look at what design flaws the existing design has in order to improve upon it. As we iterate we want to focus on improving its structural integrity and apply our knowledge of 3D printing best practices to ensure that it prints well and is built to last.


Our first step in digitally recreating the existing design involves taking photos of the armrest at the four key views: top, bottom, side, and back.


Using the four photos, we scaled and traced them in our modeling software of choice, Rhinoceros 3D, in order to get an accurate representation of the original armrest. Once we completed a design of the existing armrest, we could now analyze it and determine what kind of structural weaknesses it has.


Model Weaknesses

The primary weaknesses we found in the model were the unsupported overhang and the connection channel.


The key weakness we noticed in the original design is the way in which the “tongue” section overhangs past the supporting/connecting section (circled in yellow). Additional weight on this tongue section will cause the piece to bend, and overtime, the weak point will break.




The second weakness we noted was regarding the form of the channel that attaches the chair arm to the chair itself. The curvature is not conducive to a strong connection point and is a clear weak point during manufacturing as well.



Our Custom Solution

Overall we know we need to enhance the strength of the tongue section and the connection channel so that the overall arm is stronger and can withstand the regular stresses and strain on the piece.

In order to address the inherent weaknesses in the design we highlighted above, we made our own adjustments to the model. The following are our customizations:


Overhang




To solve the overhang issue we simply extended the connection channel until almost the end of the tongue section.





Connection Channel




To solve the channel geometry problem we altered the channel from the curvier original profile to a more sturdy triangular one.





This should finally offer us the necessary structure and support for a long lasting and easily printed chair arm.


Here are some side-by-side comparison views of the original chair armrest (in black) and our updated chair armrest (in Party Pink)



Now that we have our new and improved chair arm model, it’s time to start building! In our next chair armrest segment, we’ll be documenting our building process, which will involve rapid prototyping with our U-HIPS material.


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