Method of cutting insulation for a pipe elbow

A method of forming an insulation piece for joining with a similar piece to surround a pipe elbow, the method comprising:

• providing an outer cylindrical blade member cut from a metal plate so as to define a cylindrical body having a depth between front and rear edges of the blade member equal to the plate thickness and a thickness between two side surfaces formed by two cut lines in the metal plate, the outer cylindrical blade member including an arcuate outer blade portion extending around an angle of greater than 180 degrees and an arcuate outer holder portion extending around an angle of less than 180 degrees;
• providing an inner cylindrical blade member cut from a metal plate so as to define a cylindrical body having a depth between front and rear edges of the blade member equal to the plate thickness and a thickness between two side surfaces formed by two cut lines in the metal plate, the inner cylindrical blade member including an arcuate inner blade portion extending around an angle of greater than 180 degrees and an arcuate inner holder portion extending around an angle of less than 180 degrees;
• the outer cylindrical blade member having a diameter greater than the inner cylindrical blade member;
• mounting the inner holder portion and the outer holder portion on a holder so as to rigidly carry the inner and outer arcuate blade members substantially concentrically with a cutting edges thereof lying in a common cutting plane;
• arranging the holder to engage the holder portions of the ring members leaving an angle of the arcuate blade portions greeter than 180 degrees exposed and open at a top portion thereof;
• arranging the holder to include a back plate and a front plate between which the front and rear edges of the inner and outer blade members are clamped;
• arranging the holder to include plate portions defining two arcuate slots within which the side edges of respective ones of the inner and outer blade members are received;
• providing a table surface in a table plane at right angles to the plane and containing the center;
• arranging the holder so as to be wholly below the table surface such that only the arcuate inner and outer blade portions are exposed above the table surface;
• providing on the front edge of each of the inner and outer blade portions a plurality of sharpened, hardened cutting teeth members;
• oscillating the holder and the arcuate inner and outer blade portions thereon about an axis at right angles to the common plane and passing through the center such that the inner and outer blade portions are exposed above the table plane and reciprocate about the axis in a cutting action;
• locating a block of insulating material on the table so that one surface of the block moves across the table plane through the common cutting plane such that the outer blade portion cuts a generally circular outer surface of the insulation piece and the inner blade portion cuts a generally circular inner surface of the insulation piece;
• and guiding the movement of the block in a part circular path about a guide axis at right angles to the table plane with the guide axis located so that the blade portions cut through the block each along a part circular line at a radius of curvature from the guide axis arranged to match a respective radius of curvature of the pipe elbow.