Defining some complex shapes: Think simple contruction geometry

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I was working with a customer a few weeks ago who wanted to define a 'Pringles' shape on the end of a shaft. We got into discussing Lofts, Sweeps, Surfacing, etc. After looking at the problem, I had a flashback to high school geometry class...and a mini flashback of Mr. Kauffman's drafting class. When it comes down to it, all geometry can be broken down to some pretty simple shapes. Rather than dig my old drafting board out of the garage attic, I decided to fire up Inventor.

I have always been a fan of using construction geometry in my Inventor sketching environment to lay out complex problems. So, why should this be any different? I broke it down to what I knew:

The shaft diameter was 3 in.
The 'saddle' shape needed to have a depth of 1 in from the peak vertices to the depth vertices (at the major and minor axis, respectively).

Ok, so not a ton of info...but, all I should need.

My initial sketch would define the diameter and peak axis vertices locations. I laid this out with a circle, vertical construction line, and two points. I have all contraints visible for clarity (F8).

Next, I needed to define the 1 in depth of the shape (or the peak to valley distance; for lack of a better description). I just picked offsetting a plane 1 in from one of the origin planes as the most straight forward way to do that.

To define the minor (or horizontal) vertices, I simply sketched another circle with a horizontal construction line on the newly created work plane. I did link the diameter of this sketch to the 3 in diameter dimension parameter from Sketch1...just for added flare.

Now all my layout work appears to be done. Now time to define this shape.

I fired up a new 3D Sketch and broke out the spline tool. Using the major and minor axis vertices (or horizontal and vertical if you fancy) I defined my shape. That was a little too easy.

After turning off the visibility of all that precious layout geometry, I can isolate the shape sketch to create my 'Pringles' chip (or crisp is you prefer). Then, using the Boundary Patch tool, I can create a surface based off of the shape I have just defined.

Now that this surface is created, I could use it to Sculpt the shape off the end of the shaft, Extrude a shaft up to it, etc. Or...I could just thicken it, pattern solid bodies, and get really hungry wishing I had an actual stack of Pringles in front of me (I don't know about you, but I can kill and entire tube of Sour Cream & Onion in a single sitting).

You can use this same approach to make a variety of other shapes by adding more control points, such as: wave springs, barrel cams, etc.

No matter how complex the shape (yeah, this wasn't overly complex), I would always argue some layout/construction geometry up front will really help you out. Don't just take it from me, go out there and bisect some arcs for yourself.

...now I am off to the grocery store.

-lw