Retractable rule

In a retractable rule assembly including a housing and reel rotatably mounted in the housing and having an elongated blade formed from ribbons of metal having one end connected to said reel and extending from a position tangential to said reel outwardly through an opening in said housing assembly and when retracted within said housing assembly being in the form of an abutting volute coil, wherein when coiled, said ribbons are in substantial contact with one another and when extended from said housing assembly, said ribbons assume a tube-like structure, the improvement comprising said elongated metal blades being in the form of first and second ribbons of elongated metal, each of which having a length along its longitudinal axis, a width and a thickness, said ribbons of elongated metal being joined to one another along their lengths wherein at least the first of said ribbons is characterized as having a thickness which is variable in providing thinned regions created therein along the center of the ribbon's width wherein upon forming said abutting volute coil, said first ribbon is coiled inside of said second ribbon.

In a retractable rule assembly including a housing and reel of radius R rotatably mounted in the housing and having an elongated blade formed from first and second ribbons of metal, said first ribbon of metal being welded to said second ribbon of metal along their edges thus creating a width W between said welded edges and having one end connected to said reel and extending from a position tangential to said reel outwardly through an opening in said housing assembly and when retracted within said housing assembly being in the form of an abutting volute coil, the improvement comprising selecting the ribbon width between welded edges W and thickness of said first metal ribbon T and reel radius R such that (WT/R) is just less than the critical buckling ratio (WT/R)CR which is approximately 0.0015 to 0.0020″.

In a retractable rule assembly including a housing and reel of radius R rotatably mounted in the housing and having an elongated blade formed from first and second ribbons of metal having one end connected to said reel and extending from a position tangential to said reel outwardly through an opening in said housing assembly, said first ribbon of metal being welded to said second ribbon of metal along their edges thus creating a width W between said welded edges and when retracted within said housing assembly being in the form of an abutting volute coil, the improvement comprising providing said first ribbon having a thickness T which is greater than the thickness of said second ribbon, and wherein upon forming said abutting volute coil, said first ribbon is coiled inside of said second ribbon and further wherein said width W, first ribbon thickness T and reel radius R are selected such that (WT/R) is just less than the critical buckling ration (WT/R) which is approximately 0.002 to 0.004″.

In a retractable rule assembly including a housing and reel of radius R rotatably mounted in the housing and having an elongated blade formed of first and second ribbons of metal having one end connected to said reel and extending from a position tangential to said reel outwardly from a position tangential to said reel outwardly through an opening in said housing assembly, said first ribbon of metal being welded to said second ribbon of metal along their edges thus creating a width W between said welded edges and when retracted within said housing assembly being in the form of an abutting volute coil, the improvement comprising providing at least first of said metal ribbons having a thickness which is variable in providing thinned regions created therein along the center of the first ribbon's width whereupon forming said abutting volute coil, said first ribbon is coiled inside of said second ribbon and further wherein said width W, thickness of said first metal ribbon T and reel radius (WT/R)CR is just less than the critical buckling ratio (WT/R)CR which is approximately 0.002 to 0.004″.

In a retractable rule assembly including a housing and reel of radius R rotatably mounted in the housing and having an elongated blade formed from first and second ribbons of metal said first ribbon of metal being welded to said second ribbon of metal along their edges thus creating a width W between said welded edges and having one end connected to said reel and extending from a position tangential to said reel outwardly through an opening in said housing assembly and when retracted within said housing assembly being in the form of an abutting volute coil, the improvement comprising providing at least first of said metal ribbons having a thickness which is greater than the thickness of said second metal ribbon and which is variable in providing thinned regions created therein along the center of the first ribbon's width wherein upon forming said abutting volute coil, said first ribbon is coiled inside of said second ribbon and further wherein said width W, thickness of first metal ribbon T and reel radius R, (WT/R) is just less than the critical buckling ration (WT/R)CR which is approximately 0.003 to 0.005″.