Denys Fisher1918–2002
The Spirograph, 1965
British engineer who in 1965 turned rolling gears into the Spirograph, the toy that put hypotrochoids into millions of hands.
Spirograph
A point rides a circle rolling around another circle. Nearby pen positions build a family of fine traces, turning the familiar rosette into an engraving.
About this pattern
Denys Fisher, 1965 · hypotrochoids & epitrochoids
The gear ratios are rational, so every trace closes exactly. Inside rolling produces hypotrochoids; outside rolling produces epitrochoids. Each extra trace changes the pen offset slightly while preserving that closure.
Behind the mathematics