A motor‐driven dipping mechanism is described which has been used to make built‐upYfilms of 1000 molecular layers or more of barium‐copper stearate, using the Langmuir‐Blodgett technique. A rotating cam, the surface of which is determined by the equation &rgr;=a&tgr;, imparts a reciprocating constant linear velocity to a dipping rod holding the slide on which the film is deposited. The mechanism is counterbalanced. Available adjustments are the velocity of dipping, the length of stroke and the choice of end points, the reversal of the velocity at any time, and the orientation of the slide about a vertical axis.