Spring(s)!

Spring is in the air!  The fruit trees are blooming in the back yard and the fresh breeze is coming in gently from the newly opened windows.  With all that going on it’s hard for an engineer to keep his mind off of spring… or springs, for that matter.  Flowers and fresh air are certainly nice, but coil springs have got to be one of the most useful inventions ever conceived by the mind of man.  They store potential energy, smooth out your drive home, and even make passable works of art.

Despite their ubiquity, some people are tempted to model their springs as simple cylindrical blocks.  Ugh!  Any self-respecting engineer today should be ashamed of themselves for taking such an easy out.  Most of the time my springs look something like this.

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These are easy enough to model using a simple helix and a circular profile.

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If you’re feeling sporty, with a few more features you can even model the spring end conditions.  (Note: I realize that the spring I modeled here is pretty useless- extension on one side and compression on the other- but it does serve to illustrate the concept.)

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But what do you do when you have to model a spring that isn’t well described by a helix?  I recently had to model a spring with a non-circular cross section for a customer.  After stumbling around for a few minutes trying to ‘squash’ the helical profile I had on the screen using an old Vulcan mind trick, I found a much easier solution.

Start by extruding or revolving a surface with your desired spring profile.  In my case a simple linear extrusion fit the bill, but you could go crazy here.

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Next, and here’s the important part, create a Surface Sweep using a single line as the profile and a perpendicular line as the path. (I’ve got the first surface hidden here for clarity.)  In the Options group of the property manager select “Twist Along Path” as the Orientation type and input whatever number of turns you want to model in your spring.

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Now create an “Intersection Curve” (Tools — > Sketch Tools — > Intersection Curve) and select both of the surfaces that you just made.

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The result will be a 3D sketch with a combination of analytic and spline geometry that follows the intersection of the two surfaces.

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From here, simply create a circular (or non-circular!) profile and sweep it along the 3DSketch.  And, voila!  Now you’ve got a spring, with a non-circular profile!

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Also, lest you think that this is just another example of being able to model something in CAD that you could never manufacture anyway, there are suppliers for rectangular, oval, triangular, or custom springs (R.C. Springs is one of them).

This technique can also be used to create some really wild shapes which,  though  not very useful to engineers, might fit in quite well at your local art gallery.  Given the low cost and availability of 3D printing these days (Check out Shapeways.com) you might as well give it a shot. Who knows? Maybe there’s a flower-loving, fresh-air-breathing artist inside of you after all!

Download the CurvySpring model here.

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