A speed change auxiliary device of a lathe, comprising a base, the base having a side chamber, a side plate of the side chamber having a through groove at a central portion thereof, the side plate of the side chamber further having a side shaft hole close to one side of the through groove, and a curved slot close to another side of the through groove;
- one side of the side plate, opposite to the side chamber, being provided with a connecting plate, the connecting plate having a plate shaft hole at one side thereof and a polygonal hole at another side thereof, the plate shaft hole being pivotally connected with the side shaft hole, a screw being inserted in the polygonal hole and the curved slot, an end of the screw having a polygonal portion fitting in the polygonal hole while another end of the screw extending into the side chamber, the connecting plate being connected with a motor, a rotary shaft of the motor, which passes through the through groove, being inserted into the side chamber and connected with a driving wheel set;
- a top of the side chamber being provided with a shaft seat, a bottom of the side chamber being provided with a bottom shaft seat, an auxiliary device being provided between the shaft seat and the bottom shaft seat, the auxiliary device including a shaft, a spring, a block, an engaging member, a positioning nut, a rotary sleeve and a fixing block being fitted on the shaft in sequence;
- the shaft having a threaded section, the shaft being inserted into the shaft seat, a top end of the shaft forming an annular groove which is provided with a C-shaped snap ring enabling the top end of the shaft to be retained above the shaft seat;
- one end of the spring abutting against a bottom of the shaft seat, another end of the spring abutting against the block;
- the block and the shaft being assembled and connected together, a distal end of the block being able to lean against the side plate to have a contact with the side plate;
- the engaging member having a shaft portion and an extension plate, the shaft portion having a shaft portion through hole for insertion of the shaft, the shaft portion being connected with the extension plate, a distal end of the extension plate having an engaging groove, the engaging groove being engaged with the screw, the screw being locked by a nut to secure the connecting plate and the extension plate;
- the positioning nut being screwedly connected to the threaded section of the shaft so that the engaging member is positioned on the shaft;
- the rotary sleeve being pivotally connected to the shaft, a handle being provided at one side of an outer circumferential surface of the rotary sleeve;
- two sides of an inner circumferential surface of the rotary sleeve being provided with protrusions respectively, the protrusions each having an upright surface at one side thereof, an upper guide bevel at another side thereof, and a bottom flat surface, the upper guide bevel having a lowermost point adjacent to the bottom flat surface;
- the fixing block being disposed on the bottom shaft seat, two sides of a circumferential surface of the fixing block being provided with recesses respectively, the recesses each having a stop surface at one side thereof and a lower guide bevel at another side thereof, the lower guide bevel having an uppermost point adjacent to a top flat surface of the fixing block;
- the rotary sleeve being rotatably fitted on the fixing block so that the protrusions and the recesses are fitted to each other, the upright surface being in contact with the stop surface, the upper guide bevel being engageable with the lower guide bevel, a bottom end of the shaft passing through the fixing block and the bottom shaft seat.