When clock hands come loose on your cuckoo clock, it's almost always the result of improper winding of the hands. Clock hands are very light, fragile and bend easily. When setting the clock sometimes you bend the hands imperceptibly. When the hands make the next revolution, they contact each other. The clock gears keep turning and it spins off the splines on the hands where they fit over the shaft. This results in stripped-out clock hands that need replacing. You can buy new clock hands at a hobby shop or order them online.
Tighten the small knob on the front of the cuckoo clock hands with your fingers. It's the knob in the exact centre that holds both hands to the shaft. If the hands seem tight, wait 24 hours, check the clock occasionally to see if the hands have contacted each other.
Check the time. Check the clock hands by moving them slightly with your fingers. If the clock has lost time, or the hands are still loose, remove the knob in the centre of the hands by twisting it counterclockwise until the knob comes off.
Write down the time. Grasp the first hand, the minute hand, and lift it off the shaft. Underneath that, there is a small nut, unscrew the nut, slide it off the shaft and then lift the hour hand off the shaft.
Drop the new hour hand back on the shaft of your cuckoo clock. It may have a square hole in the hand that fits over a square fitting on the shaft. Make sure that you install it the same way the old one came off. Screw the nut back on.
Place the minute hand back on, on top of the nut. It might have small serrated splines that hold it in place, make sure the splines align with each other and slip it on the shaft referring to the time that you wrote down. Screw the retaining nut back on.
Take precautions with the hands. They do bend easily. Make sure they are perfectly straight. If you feel like you may have bent them, watch them very closely when they pass each other. If they are bent, bend them out of the way of each other.