Here's worldwidewords.com (Quinion) on "fettle""
The word was most typically used as a verb meaning to put things in order,
tidy up, arrange, or prepare. Here's an example, from Anne Brontė's
Agnes Grey of 1847, in the Yorkshire dialect speech of a servant: "But
next day, afore I'd gotten fettled up - for indeed, Miss, I'd no heart to
sweeping an' fettling, an' washing pots; so I sat me down i' th' muck - who
should come in but Maister Weston!". In northern English it can still have
the sense of making or repairing something. In Australia, a fettler is a
railway maintenance worker, responsible for keeping the line in good
shape. It's also used in some manufacturing trades - in metal casting and
pottery it describes the process of knocking the rough edges off a piece.
But all of these are variants of the basic sense. So the noun refers to
condition, order or shape, and fine fettle means to be in good order or
condition.