Cutting and replacing assembly for book glue binding machine

The cutting and replacing assembly for the book glue binding machine comprises a positioning shell, a cutting piece is movably connected to an inner cavity of the positioning shell, positioning blocks are fixedly connected to the two sides of the top of the cutting piece, positioning holes are formed in the front side and the rear side of an inner cavity of each positioning block, an I-shaped hole is formed in the bottom of the positioning shell, and the positioning blocks are fixedly connected to the positioning holes. The right side of the positioning shell is fixedly connected with a positioning mechanism, the positioning mechanism comprises a motor and a connecting block, the left side of the motor is fixedly connected with the positioning shell, the output end of the motor penetrates through an inner cavity of the positioning shell and is fixedly connected with a right-hand and left-hand threaded rod, and the two sides of the surface of the right-hand and left-hand threaded rod are both sleeved with thre