Owl Design with Frustums

Thu, 3 Apr 2014

My first draft of a circular bodied owl was based on the Owl Box project. The body was a bit on the skinny side – definitely in need of fattening up!

Rather than using a cylinder for the body, I felt a frustum was more appropriate. Luckily I have just the tool for the job…

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The owl body is made from a cone shape with the top cut off. The mathematical name for this shape is a frustum.


I made up a rough version of the body shape freehand. Cutting out a curve of card, I rolled it round and trimmed it until it was the size and shape that I was looking for.


I then measured it up ready for transfer to the computer. The important measurements are the radius of the bottom circle (r1), the radius of the top circle (r2) and the height of the model (h). I measured these dimensions and noted them down.


I then downloaded the spreadsheet from an earlier blog post here and opened it in Open Office. (It should also work in excel but I no longer have a copy after Microsoft Word and I fell out.)

I typed in the three measurements into the three arrowed boxes. The circled measurements and the angle are all I need now to construct the net of the owl frustum.

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Having decided on the size that I was after, I entered the various numbers into the spread sheet. Using the dimensions given by the spread sheet I constructed the curved part used in the owl’s body.

It all fits together rather neatly. I’ll be making the finished owl available as a download on his own then as part of the rrvs type 2 mechanism.