Dear Anne, the song is called "Shift and Spin". It was written by Ewan MacVicar who is an occasional contiributor here, I'm not sure if he's a member or not, but you could try sending him a PM. I'd provide the words but I'm not near any of my books or other resources just now.
The Chorus you refer to is
Shift and spin, warp and twine, Makin' threads coorse and fine Dreamin' o your valentine Working in the mill.
Sorry I can't help more, I'm sure someone else here can help out if Ewan's not around. In fact I've just remembered that I have a friend who sings it. I'll mail her for the words and post them.