Singer 404 problem
I bought a Singer 404 last year to work on some heavy duck cloth making covers for airplane. It has always jammed up in the bobbin area. I had it in for repair/check to see what was wrong with it and the repairman couldn't find anything wrong. But as soon as I got it home and tried to do piecing with it, it jammed again. I think he was putting the "pedal to the medal" and doing continuous stitching but when I start and stop stitching as one would do in piecing or attaching binding, the machine jams in the bobbin. Could I have a wrong size bobbin in the machine? How can you distinguish between the metal bobbins and does anyone know the correct bobbin for the 404? Any advice appreciated.