Elbow formed by cutting and method for manufacturing same

Abstract

A hole is formed in an elbow through the steps of: forming a starting hole in a material, the starting hole having an undercut remaining on a hole surface; finishing an inner diameter of the starting hole ( 11 -3 ) on one end side by revolving aside cutter (II) including an arc-shaped cutting edge and having an outer diameter smaller than a finishing hole diameter while rotating the side cutter (II) in such a posture that the side cutter (II) is inclined in a predetermined direction relative to the material ( 12 ), the revolving being carried out so that the side cutter moves along a hole surface to be finished; and finishing the inner diameter of the starting hole ( 11 -3 ) on another end side by revolving the side cutter (II) while rotating the side cutter (II).

1 . An elbow, comprising a hole having an center axis that is bent smoothly at a predetermined curvature,
 the hole having no machining remainder part inside and being a true circle, the hole having a hole surface provided in parallel to the center axis of the elbow, the elbow having a uniform wall thickness around a tube.   
     
     
         2 . An elbow, comprising a hole having an center axis bent smoothly at a predetermined curvature,
 the hole having no machining remainder part inside and being a true circle, the hole having a hole surface provided in parallel to the center axis of the elbow, the hole of the elbow having a center eccentrically located with respect to a center of an outer diameter of the elbow so that a tube wall thickness on an outer side of a bend is larger than a tube wall thickness on an inner side of the bend.   
     
     
         3 . The elbow according to  claim 2 , wherein the outer side of the bend is located at a position separated by 180° from a position of the inner side of the bend. 
     
     
         4 . The elbow according to  claim 2 , wherein the tube wall thickness is gradually increased from the inner side toward the outer side of the bend. 
     
     
         5 . The elbow according to  claim 2 , wherein the tube wall thickness on the outer side of the bend is larger than the tube wall thickness on the inner side of the bend. 
     
     
         6 . The elbow according to  claim 1 , wherein the hole has the center axis that is bent smoothly at the predetermined curvature, the hole having no machining remainder part inside and being the true circle, the hole having the hole surface provided in parallel to the center axis of the elbow,
 the elbow comprising a straight part on at least one end side of the elbow.   
     
     
         7 . The elbow according to  claim 1 , further comprising flanges at both end portions of the elbow, the flanges being integrally formed with the elbow.