Paint shakers can be used to combine two or more colours of paint evenly, to mix thinner into paint and to homogenise paints that have been left standing. Using spare parts you can build a homemade paint shaker.
Larger Paint Shakers
Large paint shakers are good for gallon-sized cans of house paint. You can make such a mixer out of an old air compressor. Remove the piston from the air compressor and replace it with a wooden rod attached to a platform to which the cans are clamped. When the compressor is turned on, the platform moves rapidly up and down, mixing the paint.
You can make smaller paint shakers using an electric motor. A container is secured to an elliptical cam (a special oval-shaped gear or connector) which in turn is attached to the motor's driveshaft. As the motor turns, the elliptical cam moves the container rapidly up and down. The bottle or pint-sized can of paint is placed inside the container and the vibrations from the motor shake the paint to mix it.
Tips on Finding Electric Motors
Many household devices have electric motors that can be removed and reused in paint shakers. Examples include hair clippers, small fans and some motorised toys. A discarded toy car, for example, could have its wheels removed and an elliptical cam attached to the motor's driveshaft which could then agitate a container.