Refilling thread on an antique Singer sewing machine bobbin spindle is a straightforward process once you understand the differences between the old treadle machines and the modern. The shape of the bobbin is one change. Rather than a round metal or plastic wheel, the bobbin is a long metal shaft with two round plates on the end. Also, the bobbin fits into its own casing, a narrow tube, before you place it in the machine.
Remove the empty bobbin spindle from the metal casing. Locate the bobbin winder, usually on the right front of the machine. It will be a holder the bobbin spindle snaps into.
Turn the knob in the centre of the balance wheel, disengaging the wheel and preventing it from running the needle. You also need to pull the bobbin winder forward so that it engages the belt.
Pull the thread from the spool at the top of the machine, drawing it down to the bobbin winder. Snap the bobbin into the winder, then tie the thread securely to the bobbin. Be sure to loop the thread over the small feed lever that will move back and forth, loading the bobbin evenly.
Start the machine by giving the balance wheel a turn and working the treadle. The balance wheel will turn, feeding thread onto the bobbin. Once the bobbin is full, remove it from the winder, cut the thread and tighten the knob on the flywheel to return the machine to sewing mode.
Slide the wound bobbin into the metal casing, making sure to leave a length of thread outside.
Pull the thread through the V-shaped groove along one side of the case. Catch the thread under the little metal tab.
Slide the casing and bobbin into the slot beneath the needle assembly, the thread lying loose. Slide the face plate closed, then turn the balance wheel bringing the threaded needle down to catch the bobbin thread. You are ready to sew.
Adjust the tension on the bobbin using a little screw near one end of the casing.