Double cylinder assembly machines automatically insert all bottom pins, top pins, springs, and closing pins into both sides of the double cylinder. Bottom pins and top (dumbbell) pins are loaded by auto feeders and springs by one spring box. An operator manually loads a cylinder inserted with cut key, a LVDT pins on next station will measure correct key numbers and later pin station will automatically load in corresponding bottom pins and top pins. Springs will be loaded on another station and checked whether they stay inside the pin holes. Alternately, the key codes may be obtained from a file. Customer can choose whether to use brass strip or brass pins to close the pin holes by hydraulic punching mechanism. Complete assembled cylinder can be checked if closed correctly and unload to the chute or to the operator when NG.