How Not to Cad (i.e. My First Cad Project)

I thought a nice next post would be to go into one of my first experiences with 3d modeling, both because it was an incredible learning experience and because it was just hillariously awful!  I 3d modeled (and subsequently 3d printed) this contact lens case with working screw tops:


it worked very well, but here’s how I 3d modeled it:

  1. Cadded a cylinder
  2. Imported a model of an M4 machine screw
  3. Cut enough threads off the machine screw to match the height of the cylinder.  Then, I copied and pasted the resulting threaded cylinder
  4. I moved the threaded cylinder into the center of the cylinder cadded in step 1
  5. Then, I did a boolean subtract so I was left with the imprint of the threads in the walls of a shelled cylinder.
  6. I then took the other copy of the altered machine screw in step 3 (since the first copy disappeared when I subtracted), and used that as part of the screw top for the lens case.
  7. I then repeated steps 1-6 again for the other cylinder to make the full lens case

Now that I think back on it, instead of forcing my chosen cad software at the time to do things it wasn’t actually capable of doing easily, I should have just bit the bullet and learned a better cad software haha.  Even though this was an absolutely horrible way to make this thing (that has made every mechanical engineer friend I told the story to cringe and die a little inside), I learned a number of things from the experience that apply to design for 3d printing in general, namely:

  1. Tolerance: make sure that if you are subtracting from a shape or shelling it, make sure you are left with walls that are 3d printable (my general rule of thumb is 3mm or more for wall thickness)
  2. orientation: be careful how you construct the male and female threads because if you orient them wrong, they will come out reverse threaded (lefty tight, righty loose) (and that totally didn’t happen to me with that contact lens case, I don’t know what you’re talking about :D)….
  3. all cad softwares aren’t appropriate for all things.  It’s the same with programming languages funny enough… you can do anything in a programming language, but there will always be programming languages that make certain tasks easier.

On this vein, the next post will talk about things that I’ve cadded and printed that turned out well!  Until next time.

John (aka The Mad Printer)

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