Adjustable mold for casting a concrete stairway

An adjustable mold for casting concrete stairways of selected different dimensions, said mold comprising:

• a longitudinal, substantially horizontal supporting frame;
• a pair of identical link arm systems defined by respective pluralities of link arms of equal length and supported on said supporting frame for displacement longitudinally thereof;
• each said link arm of each said link arm system being linked at a mid-length position thereof by a respective center pivot to a respective said link arm of the other said link arm system, such that said link arms of said pair of link arm systems are coupled successively in pairs of arms with the respective said center pivot of each said pair of arms being positioned along a longitudinal center line of said pair of link arm systems;
• said arms of said pairs of arms having opposite ends linked by respective end pivots to respective ends of arms of successive adjacent pairs of arms, such that said end pivots are located in pairs on opposite sides of said longitudinal center line with said end pivots of each pair of end pivots being positioned along a line extending transverse to said longitudinal center line;
• a plurality of step units, each said step unit including an instep and an upstep, each said instep having a transverse edge resting against an upstep of an adjacent step unit;
• means, mounted on said end pivots of each said pair of end pivots, for supporting each respective said step unit for vertical pivotal movement about a respective axis extending along a lower end of the respective said upstep;
• means for moving at least one of said center pivots longitudinally of said supporting frame, thereby effecting simultaneous extension or retraction of said pair of link arm systems, and thus adjusting the spacing between steps to be formed by adjacent said step units;
• and
• means for adjusting the relative angular position of said step units about said axes thereof.