Main cam for a buttonhole sewing machine

Abstract

A main cam of a buttonhole sewing machine has four cams connected together in an assembly which includes a drive disk switch spring. A worm hub and a drive disk are connected together. A shifter mechanism has right and left shifter arms and springs which periodically capture and release the drive disk switch spring. The drive disk and worm hub are driven by a worm gear on the main drive shaft. One of the shifter arms holds the switch spring in a detent, disengaging the switch spring from the drive disk while the buttonhole sewing machine sews bight stitches along a first side of the buttonhole site in a workpiece. The workpiece is clamped between a clamping plate and a clamp. The clamping plate moves in steps while the needle is up. When the clamping plate reaches the end of the intended buttonhole a shift plate is moved, moving the shift arms, releasing the switch spring from the first switch arm and positioning the second switch arm for capturing the switch spring. The switch spring engages the drive disk and drives the cam until the switch spring is captured in the second arm. While the switch spring is moving the multiple cams, the feed cam disengages the feed and a barring cam and follower move the clamp plate laterally to form large barring stitches at the end of the buttonhole site.