Report "I have a White Heavy Duty sewing machine model # 1919 serial #19374.The problem I am having is this: While sewing the the inner part of the large knob on the side of the machine works itself loose. I realize it is suppose to looosen when you don't want the needle moving up and down but it does it on it's own and causes the machine to stop sewing. How can I stop this from happening? I purchased this machine quite a few years ago and have no place locally to take it to be serviced"