Abstract: A chainstitch machine has an edge trimmer knife driven in vertical chopping motion adjacent the needle by a linkage actuated by an oscillating shaft that operates synchronously relative to stitch-forming components. The linkage includes a bracket oscillated by the shaft and a joint movable along the bracket between a first position, in which the axis of the joint is offset from the axis of the shaft to communicate oscillating movement to the knife, and a second position, in which the axis of the joint is concentric with the shaft and transmits no oscillatory movement. In the second position, the knife is retracted by the linkage to a location above the region through which work pieces move, but in the first position, the linkage moves the knife down so that part of the knife extends through the plane of the throat plate and is pressed against an edge of a throat plate insert by a small pressure slide entirely within a notch in the insert and guided by juxtaposed edges of the notch.