Hello Mowerfreak
Fully enclosed cabins have been used on ride-on mowers since the 1960s.
Roll-over bars and canopies are more common, of course.
Yes, there were concept mowers (first image c1950s), but Horwool was certainly using
an enclosed cabin in the late 1960s or early 1970s.
As lawnmowers became larger they seemed to follow the trend for
the ergonomics enjoyed in agriculture.
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Jack