Hi Mishap.
I know what you mean about the reel of thread jumping about because you can't put the plastic cap thingy on. When I first had my machine, I didn't even realize that you were meant to put that on (I did wonder what it was for though!), and at times the reel made a lot of noise as it jumped about. However, apart from the noise, mine didn't cause any other problems.
I hope you don't mind my asking, but have you double / triple / quadruple checked that you are threading the machine correctly? Aside from the jumpy reel, the problem sounds typical of a wrongly-threaded machine.
I'm sure you will have checked that already, but thought I'd better mention it just in case
Being moved along by someone who "wants your place".
Is there anyone who still thinks that Israel's actions in Gaza are justifiable?
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