Patent ID: 8506006

Claim:
A truck frame for a construction machine, said truck frame including left and right side frames and a center frame disposed between said side frames, comprising: said center frame being constituted by a top plate and a bottom plate which are connected to said left and right side frames at an interval in a vertical direction, a connecting tubular body provided between intermediate portions in left and right directions of said top plate and said bottom plate to connect said top plate and said bottom plate, and a cylindrical circle member which is secured to an upper surface side of said top plate and on an upper end side of which a swing circle is mounted, said circle member is formed such that its upper end side is formed as an upper thick-walled portion, its lower end side is formed as a lower thick-walled portion, each of said upper and lower thick-walled portions having a same plate thickness, an outer curved portion is provided in an outer peripheral surface of said circle member, said outer curved portion being located between said upper thick-walled portion and said lower thick-walled portion and formed by cutting out a recessed groove shape over an entire circumference, an inner curved portion is provided in an inner peripheral surface of said circle member, said inner curved portion being located between said upper thick-walled portion and said lower thick-walled portion and is formed by cutting out a recessed groove shape over an entire circumference, and a portion between said upper thick-walled portion and said lower thick-walled portion is formed as an hourglass-shaped thin-walled portion having a smaller plate thickness than the plate thickness of said upper and lower thick-walled portions and enclosed by said outer curved portion and said inner curved portion.