Turn the vertical driving cam to the position where throat plate surface 3 and needle tip 4 align with each other , and the first or the second tooth of the top end of feed dog 5 descends from the throat plate surface 让针尖4与针板上面3对齐，在送布牙5的前端1 2齿从针板上面下沉的位置，转动上下传送凸轮，进行固定。
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