I frequently fill from a thread cone so don't always get the thread through the path the same way as I would from a spool. I found that putting a little tension on the thread coming from the cone by holding it between my thumb and forefinger and guiding the thread up and down on the bobbin helps avoid wonky bobbins. Also, don't forget to clip off the little thread tail on the top of the bobbin where you start the thread. It will cause a problem in the bobbin case.