The invention provides an externally-square and internally-
circular coil pipe and a
machining device thereof, and relates to the technical field of externally-square and internally-circular devices, the
machining device is mainly composed of a
machining table, a
cutting machine, a coil
pipe body and a fixing device, the
cutting machine is arranged at the upper end of the machining table, the coil
pipe body is placed at the end, close to the
cutting machine, of the machining table, and the fixing device is arranged at the end, opposite to the cutting machine, of the machining table; and the fixing device comprises a sliding rail, the bottom end of the sliding rail is welded to the machining table, the sliding rail is in an I shape, the end, away from the machining table, of the sliding rail is slidably connected with two connecting plates, the ends, away from the sliding rail, of the connecting plates are slidably connected with two clamping plates, and the ends, close to each other, of the two clamping plates are fixedly connected with first springs. According to the externally-square and internally-
circular coil pipe and the machining device thereof, the fixing device is arranged, and the problems that in the existing cutting process, a pipe is manually held by hand, one end of the pipe is placed into a cutting machine to be
cut, due to
instability of manual holding, pipe cutting deviates, and the end opening of the
cut pipe is not smooth enough are solved.