My own fault, because I left it overnight without a cover on intending to go back to a job next day, then was stuck indoors with flu. Rusty rainwater has dripped from the asbestos roof support angle iron which runs at right angles above the lathe bed. There is an inch wide band of raised rust across the (Myford) bed. What's the best way to remove it?
Your probably going to be stuck with mechanical cleaning.
Soak in WD40, while it's soaking make yourself a scraper out of a piece of aluminium bar or flat just file the end to a flattened chisel shape then remove the loose rust. Clean off as much as you can. A small brass brush works well too. Scotchbrite pad clean, then rub vigorously with the aluminium again, it works well, it fills the pores with aluminium which supposedly reacts with the rust to form aluminium oxide and iron. (technique used by car restorers on chrome bumpers etc)
If there's bad pitting, your stuck with it, what's gone is gone.
For small parts very strong tea works well, albeit slowly. The best way is electrolysis using washing soda, but it could be impractical for a large object or a small area on a large object.
Finally, fix the roof - even if you only fix a sheet of polythene under it for now, get it done ;)