Abstract: An apparatus for cutting spirally formed pipe is disclosed. This apparatus has two knives mounted on a boom to be positioned inside of the pipe. The inner knives have cutting edges that are adjacent the inner pipe surface and point in opposite directions. Two knives are also positioned outside of the pipe. Each outer knife is positioned opposite of one of the inner knives. The outer knives are continuously reciprocated toward and away from their respective opposed inner knife. The reciprocating outer knives are maintained in a position clear of the pipe while the spiral pipe is formed. The reciprocating outer knives are moved to a cutting position where their cutting edges move into and out of an overlapping relationship with the cutting edges of their respective inner knives to cut the pipe.