This invention relates to the pipe lathe art, and more particularly to a pipe lathe which mounts on the pipe for conducting work on the pipe.
Pipes are fabricated of numerous different materials including metal, cement, and plastic. The present invention primarily concerns portable pipe lathes for fiber glass reinforced plastic pipe ranging in diameter from approximately 50 mm. in diameter to 1500 mm. in diameter.
The installation and laying of pipe may require the cutting of pipe lengths and preparation of the pipe ends prior to the fitting of the pipes together. The pipe is prepared in the factory with standard lengths cut or molded and the ends threaded, tapered, shaved, or ground as needed. However, the same procedures need to be available in the field to fit standard lengths of pipe into special situations, to remove oxidation and other impurities prior to assembly, to salvage partially damaged lengths, and to prepare non-standard lengths when required.
The plastic in the fiber glass reinforced plastic pipe reacts with the atmosphere and is changed by exposure to sunlight after fabrication. In order to assure satisfactory bonding between adjacent lengths of pipe or between a length of pipe and a coupling, the outer surface of the pipe near the end must be prepared prior to assembly. Several methods of surface preparation are available including the use of solvents, sanding, grinding, and scraping.
One joint is called the butt and wrap. The ends of the two pipes to be joined are ground or scraped to taper the ends and prepare the outer surface for bonding. The ends are then butted against each other and resin saturated glass reinforced cloth is wrapped around the joint.
Another joint is the bell and spigot. The end of one pipe is flared into a slight bell during fabrication. The end of the pipe to be joined to the bell is prepared in the manner described for the preparation of the ends for the butt and wrap joint. The taper of the spigot end must be the same as the taper inside the bell in order to achieve a satisfactory joint. The spigot may be tapered at the factory during fabrication or made to fit in the field. Prior to assembly, the ends are cleaned with a solvent or by light sanding. Bonding material is then applied to both ends and the spigot is inserted into the bell.
Molded couplings and fittings are also available for assembly and come in a variety of shapes and sizes. Many have bell shaped tapered openings. The preparation of the pipe end to be inserted into a bell shaped opening is identical to the preparation of any tapered spigot.
Threads may also be used for assembly. For example, the inside of a bell coupling on the end of a pipe may be threaded to match a threaded spigot on the end of another pipe.
Tapering tools have been developed for use in the field. One type is the scraper. A mandrel is inserted into the end of the pipe after it is cut to length. Each size of pipe has a different mandrel. A frame having an arm with a tool holder is fitted onto the mandrel. The tool holder is set at the desired taper angle. A scraping blade, similar to a large razor blade, is fitted into the tool holder with the blade in a plane perpendicular to the outside of the pipe in the longitudinal direction and with the blade cutting edge at the desired taper angle. The frame is then rotated either by hand or with the aid of an electric or pneumatic motor. The taper produced is determined by the set of the blade in the tool holder.
Another method of making the taper is by grinding. A grinding wheel set at the desired taper angle and powered by an electric or pneumatic motor is substituted for the tapering blade. The grinder tends to be faster than the blade but is costly, ackward, and introduces the problem of dust. The large size of the grinder may also be a problem when pipe end preparation is required in close quarters. The most basic grinding method omits the mandrel and requires the operator to manually and visually judge a proper grind depth and angle as the grinder is moved about the outside of the end of the pipe.
Single point contact cutters, similar to tools found on bench lathes, have been successfully utilized in field pipe lathes which provide for automatic longitudinal progression of the cutters along the pipe as the cutters are rotated around the pipe. Most have been developed for work on asbestos-cement pipe. Pilot Manufacturing Company in Torrance, Calif. makes several sizes of longitudinally feeding field pipe lathes utilizing single point contact cutters. The automatic longitudinal feed is achieved by providing spiral threads coupled to an arbor shaft positioned inside the pipe and engaging spiral threads on a hub carrying the cutter. As the hub rotates, the hub is screwed along the arbor shaft by the threads causing the automatic longitudinal progression of the cutter down the outer surface of the pipe. The depth of cut is not varied during the progression. If a shallow cut is needed, a single machining pass may be sufficient. If a deeper cut is desired, additional machining passes may be required. The advantage of the single point cutter is that all of the cutting force is concentrated on a narrow point requiring less power to turn the cutter than the wide scraping blades discussed above. Also, a point support may be used inside the pipe rather than the larger area mandrel support required with scraping blades.
The present invention combines an automatically progressing longitudinal feed with an automatically progressing radial feed allowing a single point contact cutter to be utilized to automatically produce a tapered end. Disengagement of the radial feed allows the lathe to produce a straight tenon cut. Disengagement of the longitudinal feed allows the lathe to make a groove or cut off the end entirely depending upon the depth of the cut.
The longitudinal feed is achieved as described above by spiral threads coupled to an arbor shaft engaging spiral threads on the hub. The radial feed is achieved by providing two sprockets, a chain between the sprockets, shafting, and gearing on the cutter holder. One sprocket is located on the arbor shaft and does not rotate in relation to the arbor shaft. The other sprocket is located on the frame. As the hub and frame rotate, the non-rotating sprocket induces rotation in the frame sprocket directly related to the rotation of the hub on the arbor. The rotation of the frame sprocket is transmitted to the cutter holder through suitable gearing to automatically move the cutter radially. The combination of the automatic radial and longitudinal progressions of the cutter produces a taper on the end of the pipe.
As the advantages of fiber glass reinforced pipe have become increasingly recognized, the potential demand for an automatically tapering field pipe lathe has grown. The present invention makes possible the automatic cutting of precision tapers at any desired angle by changing one or two sprockets. The present invention is also adjustable to fit any diameter pipe and to make straight tenon cuts, grooves, and cut offs. The lathe is able to operate on pipes having walls with variable initial thicknesses and ones that are flexed out of round, since the cutting is between the cutter on the outside of the pipe and a wheel or roller riding on the inside of the wall, instead of the distance between the cutter and the arbor or mandrel as found in other lathes.
Other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.