Hello, Group!    I have read several massages that the bobbin winding on some machines is less than satisfactory. I have found that my bobbins were winding unevenly on my MC500 machine. After eliminating some obvious things, like tension, bad thread, etc, it dawned on me that I was storing the "hump jumper" tool that comes with the machine, in a place just to the left of the bobbin winding post. The contour of the hump jumper tool fits perfectly in that space, but the tool interferes with the thread coming from the guide to the far left of the machine and going onto the bobbin.  It does not allow the thread to wind properly onto the lower area around the bobbin's core.   SO, if you also store your hump jumper there--remove it while winding a bobbin.  It makes a great storage space fior the tool, but not so great when  you are trying to wind a bobbin.
Take care, be safe and healthy
Kathy Strabel   Camas WA