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Adjustments in the Singer double pile “button” speed controller. Note: It is the adjustor’s obligation to determine if they un- derstand these adjustments and are qualified to make them. The variable speed of the controller is adjusted with the screw that is shown below. Inside the porcelain block are two rows of carbon disks. As the button is pushed, the disks are squeezed tighter together, and more current flows to the motor. During less than full speed, the excess current is turned into heat. The controller depends on moments between depressions, when it should be completely released, for the controller and motor to cool down. If the screw is too loose, the speed will be too slow until the full speed contacts come together. If the screw is too tight, the control will not stop the current flow when the button is released, and both the controller and the sewing machine motor can seriously overheat. These controllers have no “positive shut- off,” so it is very important that they be set in such a manner that the controller can cool off between times that the button is de- pressed. In the picture to the right, is the lock nut that must be re- leased before adjusting the speed adjustment screw. Above the lock nut, is the plate that completes one side of the contacts for the full speed. The plate can be moved on the screw if necessary, but in most cases, the full speed setting can be set by bending the two copper contacts far- ther or closer from/to the contact plate. Ideally, the speed adjustment screw should be set so that current does not flow until the button makes a significant move, and the full speed contacts should take over when the speed control has reached its maximum speed.
