Ring 144/96, wheel 72

A reader asked whether the hole numbers on the Spirograph wheels correspond to the distance from the edge in millimeters. The answer is “not quite”. They are very regular, however, which is one of the reasons that the designs are so interesting and appealing to the eye.

So how to measure how far apart the holes are from each other in terms of the radius of the wheel?

It’s hard to tell by looking at the wheels, because the holes are laid out in a spiral. That’s because the diameter of the holes is bigger than the radial distance between them. If the holes were laid out in a line, they would overlap. The integrity of the round holes would be gone. You wouldn’t be able to draw patterns, and the wheel wouldn’t hold together.

However, when you draw a design like this one, you line up each hole at the same spot on the ring before you draw its individual pattern. Let’s look at the lines drawn by the holes in this pattern and measure the distance between them.

This pattern is drawn using holes 1, 3, 5, 7, 9, 11, 13, 15 and 17. It was drawn with my old Spirograph.

Since the distances are small and hard to measure individually, let’s measure a number of them together and divide.

From hole 1 to hole 17, with the best accuracy and precision as I can manage with my little vernier caliper, is 10.4 mm (0.409 in).

Divide 10.4 mm by 16, because there are 16 spaces between holes 1 and 17, and you get 0.650 mm (0.0256 in).

My result: 0.650 mm (0.0256 in).

This result should be independent of the size of the holes and the size of the pen used, as long as the holes are the same size and you use the same pen throughout.

I also think it’s the same with all the wheels, because that’s how the designers of the set made it. To my eye, all the patterns produced have a similar distance between the lines, but I haven’t measured this yet. I hadn’t actually asked myself the question until doing this, but I’ll experiment and report in a future post.

I used the wheel and ring from my old Super Spirograph set for this particular drawing. Comparing designs made with the old set and the new set shows that the old set is more precise. I’ll make more posts about that in the future. Quality really shows when you’re drawing fine lines close together.

Like any good scientific experiment involving measurements, others should try it themselves and see if they can replicate my results. Let me know how you do in the comments below.

(Hmmm…. my inner science teacher is showing!)

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