Overlocker

Also called a serger. I messed about with mine for hours. I changed the thread colour and retreading is, shall we say, a challenge.  I'm not sure how anyone non-technically minded would get on. Eventually I got it working. My sewing machine started to clunk a bit so I decided to take out the shuttle race and clean and oil it. It didn't go back easily- but I persevered and got it sorted Eventually.