Week 5/6: CAD Design Challenge

What was challenging: oddly, I struggled most with TinkerCAD and OnShape.  I am definitely not proficient in Fusion 360, but I apparently have developed a little bit of intuition for it – and I had a hard time translating my thinking to the other apps.  I couldn’t find options and commands quickly enough to get anything done in the 1 hour time limit.  So I just decided to use Fusion 360. 

Overall dimensions: 1.0” x 1.0” x 0.375”

If I had more time: I would experiment with flexibility and tolerances – adjusting the size of openings and the thickness of the printed material to see if I could get it to fit multiple sizes of pencils (and maybe use less filament to save cost and time) without breaking. 

How did I use materials: I picked a particular pencil to give myself a constraint to work to.  Now that I look back at the design brief, I see that I did not make it to fit any pencil – so that doesn’t meet one of the requirements of the brief.  However, I thought the Diresta pencils I designed for were on theme, since I bought them to support a maker who is active in building the maker community.

How did I use design thinking: I didn’t have time to print and test multiple versions, but I did do quite a bit of iterating/revising in my head and in the software.  My initial ideas were something that would clip around the barrel of the pencil (like the separate, metal piece that snap onto some mechanical pencils and function as the pocket clip) and have a long skinny piece that would stick out, perpendicular to the pencil, to prevent it rolling.  That seemed cumbersome for writing and too easily broken though – and I didn’t think I would like the aesthetics.  I was stuck on ideas like that for a while until I realized I just needed a flat spot on one side to prevent rolling.  I envisioned starting with a solid cylinder a bit larger, in diameter, than the pencil. 

I planned to just cut a smaller, concentric cylinder out of it to make a tube for the pencil to slide into, and then cut a flat spot along one side.  I wasn’t sure how to quickly figure out the tolerances to get the right amount of friction, so I decided I shouldn’t have a closed tube.  It should be open along one side.  Then it would be flexible enough that I could make it slightly undersized, so it would expand slightly when I pushed the pencil in – ensuring that it would squeeze a bit and stay in place.  I realized I could accomplish that and leave myself plenty of space for the flat spot if I didn’t make the cut cylinder perfectly concentric in the main body.     

So I was several design modifications in when I started to actually model it.  In the software, I offset the cut cylinder to the side far enough that it created an opening exactly opposite where I would put the flat spot on the other side.  Then I used the software to visually decide where to cut the flat spot, so that it looked like the remaining material was a reasonable thickness.  Once that was done, there were a few other places that looked too thin, so I trimmed them a bit (which opened up a larger gap to expose one side of the pencil a little more.  And there were other spots that looked a little too thick and I worried they wouldn’t be flexible enough, which might concentrate stress on narrower spots and cause them to break, so I trimmed the ticker parts a bit as well.  At that point I was ready to print it and see if it functioned as I intended. 

However, it didn’t yet have an additional feature that would add value (I thought about customizing it with a sticker on the flat spot - or adding some text to the model).  Then I remembered that the pencil I was modeling had text on opposite sides.  I decided to modify my design by mirroring it to have 2 spaces to hold pencils.  So now it can store 2 pencils, which makes it possible to display the whole text, and I can just pop one out to write. 

 

As the prototype was printing, I had one last inspiration.  Since I had customized it for Diresta merch, I decided to make one side fit my Diresta Ice Pick (I just got it a couple weeks ago, because I wanted to be like the other cool (maker) kids.)