The lengths of the links comply with the conditions: A͞B=D͞C=A͞F=D͞E and B͞C=E͞F. Cranks 1 and 1' are keyed on shaft A and cranks 2 and 2' on shaft D at arbitrary but equal angles, not equal to 0° or 180°. As a result, there will be no uncertainty of motion at the extreme positions (dead points) of the mechanism.
$629$LW,PC$