Show Me Your Typical Sections

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Show Me Your Typical Sections

2018-11-01T21:26:54+00:00By |Article, Design, Engineering|

Show Me Your Typical Sections

George Opie was my first boss.  I got lucky.  Opie was the head of our design department at an automotive supplier in the mid 90’s.  We were past the days of drafting boards, but George started his career as a draftsman.  He loved to regale us with tales of working on the Corvette program and run-ins with famous car designers and execs.

In those early days of CAD, computer horsepower was limited and expensive.  Sound fundamentals couldn’t be overcome with flashy graphics.  CAD is so fast now that it lulls you into thinking you should just jump into a design and figure things out as they come up.  I learned 3 fundamentals from George that are less obvious today so they bear repeating.  I’ll save for another article his golf tips and rule that if you drink more than 2 martinis at lunch nothing good ever comes from returning to the office that day.

  1. Stay off CAD as long as you can before jumping in
  2. Develop your typical sections
  3. Don’t paint yourself into a corner

Stay Off CAD as Long as You Can Before JumpingIin

Back when Silicon Graphics workstations cost as much as a starter home, they probably had less graphics power than my iPhone.  And while we had just started using parametric modelling, it still took time to get your ideas into CAD.  The biggest problem with getting your ideas into CAD is that for some reason you become less open to changes.  I don’t know why we are more willing to change a paper sketch.  I have a couple of theories.  When I sketch, it’s clearly not perfect so if there’s a better idea that comes along, I can’t lie to myself that the sketch was already perfect.  When I have a design in CAD, it’s rendered flawlessly.  As far as we can tell, it IS perfect.  Why change it.  Another theory is that once you’ve invested time in CAD, you don’t want to feel you wasted that time.  I’m not sure why sketches don’t create the same response.  Maybe it’s all the movie scenes of a great artist or writer crumpling sheet after sheet of paper and tossing them into a wastebasket.  The growing pile of wadded paper is a cinematic emblem of creative effort.  Those scenes give us permission – even incentive to trash our sketches over and over again until they are good enough.

So work your ideas on paper, or the whiteboard, or foam core, or even legos.  Just keep them out of CAD until you can’t progress any further without it.

Section shows detail other sketches may not

Develop Your Typical Sections

A cross section is a view on a drawing that is a two-dimensional representation of what it would look like if you literally cut through your design.  There was a pretty cool exhibit at the Museum of Science and Industry in Chicago, Body World, that had actual cross sections of a human body.  A typical section is a cross section that represents the major details of your design.  Quite often it’s a section that runs down the center of your product or cuts through major fastener details.  When I’d get stuck on a design and look to Opie for advice, he’d always start with “Show me your Typical Sections”.

It’s easier to think about a design in the simplified format of 2 dimensions before moving into 3 dimensions.  So if you take the time to sketch out your typical sections, you’ll usually identify problems before you get started in CAD.  Many times you’ll recognize all the stuff that has to fit in your product and you move features around in your sketch before you get into CAD.  You can learn a lot from a sketched section.  You can work out die-draw (the way an injection mold opens and closes).  You can calculate clearances and how much space you’ll need for wall thickness, adhesive, fasteners, gaskets, compression.  I often go over my section sketched with colored pencils or highlighter to clearly separate different parts.  In a technical drawing, that’s usually done with cross hatching, but colors are easier to read on a concept sketch.  Sometime on really complex designs it’s even useful to move from paper into a 2D sketch on the computer to get more accurate.  It’s still easier to change than 3D and you’ll learn a lot.  It’s also a good communication tool to explain your idea to collaborators or customers.  You can get away with pitching crazier ideas on paper or in section than you can in 3D.  Then if the crazy idea turns out to be garbage it’s not a big deal.

Don’t Paint Yourself into a Corner

We all know the analogy of painting yourself into a corner, and while it’s obvious when painting a floor, it’s not obvious in design.  What I call getting painted into a corner is this: You start working on certain (often easy) aspects of a design so you can feel like you’re making progress.  Once you start getting a few details nailed down, you start into the harder stuff and realize you either need more space in your design, or need a complete redo of your previous work.  The worst case scenario is that you compromise the difficult detail because you don’t want a complete redo of the earlier features.  The best way to NOT get painted into a corner on a design is:  1) Stay off CAD as long as possible, 2) develop your typical sections, 3) Start with the hard stuff first.

I have a coworker, Don, who is very experienced and I’m often perplexed by how he seems to make no progress early on in a project and then suddenly he’s half done.  Others I’ve worked with in the past would have tons of CAD done in the first few hours.  Then those guys would find (or worse ignore) problem after problem where Don had taken his time up front to figure out the hard stuff, identify risk, sketch it a bit, get organized.  Fundamentals over software.  Opie would have liked Don.  The seemingly slower and thoughtful approach reminds me of the old joke about the young bull and the old bull but that’s not appropriate here.