Chair seat adjustment assembly

A chair seat pitch adjustment assembly having first support means, a seat support member pivotally mounted with respect to said first support means at one point and adjustment means interconnecting said seat support with said first support means for adjusting the angle of said seat support member with respect to said first support means, the improvement in said assembly comprising:

• said adjustment means including a pivot bracket pivotally mounted to said first support means on one pivot axis and to said seat support member on a second pivot axis;
• said pivot bracket including a cylindrical wall extending generally laterally with respect to the sides of said seat support member, said cylindrical wall defining at least a portion of the wall of a right circular cylinder whose axis of revolution lies on said second pivot axis;
• said cylindrical wall including at least one helically oriented slot therein;
• a slide slidably mounted on said seat support member for generally lateral movement with respect to the sides of said seat support member, said slide including projection means projecting through said helical slot in said cylindrical wall whereby as said slide is moved laterally, said cylindrical wall and therefore said pivot bracket are rotated about said second pivot axis, thereby changing the relative elevation of said first pivot axis with respect thereto and thereby changing the pitch of said seat support member with respect to said first support means;
• means allowing at least one of said pivotal mountings between said seat support member and said first support means, said seat support member and said pivot bracket and said pivot bracket and said first support means to shift when said pivot bracket is rotated;
• said seat support member including a wall having a generally rectilinear slot therein extending generally laterally with respect to the sides of said seat support member;
• said projection means on said slide extending through said generally rectilinear slot;
• and an insert of semi-cylindrical configuration corresponding to the configuration of said cylindrical wall and being seated therein, said insert including a helical slot therein aligned with said helical slot in said cylindrical wall.