Method of making a composite metal and plastic level

Claim 1

A method of making a spirit level having an elongated level body of generally rectangular cross section with a pair of relatively parallel edge faces and a pair of relatively parallel side faces comprising: forming an elongated metal frame having four relatively parallel rails arranged in a transversely rectangular array to extend along the four lengthwise extending corners of the level body and internal web portions rigidly interconnecting the rail portions and spaced inwardly of the rectangular array to define a longitudinal channel at each of the four sides of the array, providing a first pair of mold members having opposed edge face forming surfaces and relatively moving the first pair of mold members in a direction laterally of one pair of relatively parallel sides of the array until the edge face forming surfaces are firmly pressed against the rails at said one pair of relatively parallel sides of the rectangular array and close the outer side of channels thereat, providing a second pair of mold members having opposed side face forming surfaces and relatively moving said second pair of mold members in a direction laterally of the other pair of relatively parallel sides of the rectangular array until the side face forming surfaces are firmly pressed against the rails at said other pair of relatively parallel sides of the rectangular array and close the outer sides of channels thereat and form a mold cavity around the frame, introducing a flowable plastic material into the channels of the type hardenable to form a rigid plastic body, allowing the plastic material to harden in the channels to form a rigid plastic body on the metal frame, and separating the mold members from the composite metal frame and rigid plastic body to provide an elongated level body with the outer faces of the four rails exposed at its four lengthwise corners to provide accurate level surfaces, and mounting level vials on said level body.

Claim 2

A method of making a spirit level having an elongated level body of generally rectangular cross section with a pair of relatively parallel edge faces and a pair of relatively parallel side faces comprising: forming an elongated metal frame having four relatively parallel rails arranged in a transversely rectangular array to extend along the four lengthwise extending corners of the level body and internal web portions rigidly interconnecting the rail portions and spaced inwardly of the rectangular array to define a longitudinal channel at each of the four sides of the array, providing a first pair of mold members having opposed edge face forming surfaces and relatively moving the first pair of mold members in a direction laterally of one pair of relatively parallel sides of the array until the edge face forming surfaces are firmly pressed against the rails at said one pair of relatively parallel sides of the rectangular array and close the outer side of channels thereat, providing a second pair of mold members having opposed side face forming surfaces and relatively moving said second pair of mold members in a direction laterally of the other pair of relatively parallel sides of the rectangular array until the side face forming surfaces are firmly pressed against the rails at said other pair of relatively parallel sides of the rectangular array and close the outer sides of channels thereat and form a mold cavity around the frame, introducing a flowable plastic material into the channels of the type hardenable to form a rigid plastic body, allowing the plastic material to harden in the channels to form a rigid plastic body on the metal frame, and separating the mold members from the composite metal frame and rigid plastic body to provide an elongated level body with the outer faces of the four rails exposed at its four lengthwise corners to provide accurate level surfaces, and mounting level vials on said level body.

Claim 16

A method of making a spirit level having an elongated metal body of generally rectangular cross section with a pair of relatively parallel edge faces and a pair of relatively parallel side faces comprising: forming an elongated metal frame having four relatively parallel rails arranged in a transversely rectangular array and web structure rigidly interconnecting the rails and defining channels at least at opposite sides of the array, forming openings in the web structure between said channels, providing a pair of mold members having opposed side face forming surfaces of a resilient mold making material, and pressing said side face forming surfaces against the rails at relatively opposite sides of said rectangular array with sufficient pressure to compress the portions of the side face forming surfaces that engage the rails and offset the portion of the side face forming surfaces intermediate the rails slightly inwardly of the outer faces of the rails, introducing a quantity of rigid urethane foam reaction mixture into the channels having a free rise volume greater than the volume of the channels and a density in a range of about 20 to 30 pounds per cubic foot, allowing the reaction mixture to expand and set in the channel to form a rigid foamed plastic body on the metal frame, separating the mold members from the composite metal frame and rigid plastic body to provide an elongated level body with the outer faces of the rails exposed and with the outer faces of plastic in the channels offset slightly inwardly from the outer faces of the rails, and mounting level vials in said level body.

Claim 17

A method of making a spirit level having an elongated metal body of generally rectangular cross section with a pair of relatively parallel edge faces and a pair of relatively parallel side faces comprising: forming an elongated metal frame having four relatively parallel rails arranged in a transversely rectangular array and web structure rigidly interconnecting the rails and defining channels at least at opposite sides of the array, forming openings in the web structure between said channels, providing a pair of mold members having opposed side face forming surfaces of a resilient mold making material, and pressing said side face forming surfaces against the rails at relatively opposite sides of said rectangular array with sufficient pressure to compress the portions of the side face forming surfaces that engage the rails and offset the portion of the side face forming surfaces intermediate the rails slightly inwardly of the outer faces of the rails, introducing a quantity of rigid urethane foam reaction mixture into the channels having a free rise volume greater than the volume of the channels and a density in a range of about 20 to 30 pounds per cubic foot, allowing the reaction mixture to expand and set in the channel to form a rigid foamed plastic body on the metal frame, separating the mold members from the composite metal frame and rigid plastic body to provide an elongated level body with the outer faces of the rails exposed and with the outer faces of plastic in the channels offset slightly inwardly from the outer faces of the rails, and mounting level vials in said level body.