Its raining, a legitimate day off work (no gardening in the rain).
So, sorting out a few rusty Singer bobbins off my 221K and 201K
Why do they go rusty?
If cotton is left on them, it attracts moisture which then rusts the bobbin. I used to be a lace maker, lacemaking uses 100% cotton fine threads. They dry out on the pillow which causes them to snap (especially when you leave them on the back parcel shelf of your mini when taking your lace on holiday with you, doh), the cure was to leave a damp cloth over the pillow and threads to put moisture back into the thread to prevent snapping.
So the dilemma is to remove all the thread when you finish your project or leave it on the bobbin? Its not going to rust that quickly so no real need to remove the thread (I hate wasting thread) BUT if you buy/have old bobbins that haven't been used for donkey's years with thread on, remove it. Its surprising just how many different threads can be on one bobbin. On the really old ones, the thread is sometime rusted in, you can use a blade to cut the thread but mind your fingers.
This is what you might find.
Easy fix, I used a small file that I found in an old attachment box, its ideal to file away the rust.
Wind the wire wool around the bobbin then twist the ends tight. Twizzle the wool around the bobbin for a final polish. Then give it a good clean with a cloth, I used a bit of off-cut of wadding.
It doesn't take long to get rid of the rust, it will stay away as long as you don't leave thread on for too long. My instinct is to put a bit of oil on it like you do where you have removed rust from any other part of the machine but this will mark the thread so best not to do it.
All clean and tidy, tucked up in a modern box.