Modern Machine-Shop Practice Part 165

[Ill.u.s.tration: Fig. 2465.]

Fig. 2465 represents a pipe cutter in which are a pair of anti-friction rollers and a severing tool bevelled on one edge only so as to leave the end of the pipe face cut square, and the piece cut off bevelled on its face; or by turning the cutter round the reverse will be the case, the piece cut off being flat on its end.

The action of this cutter is, as in the case of the wheel cutter, simply that of a wedge, hence no cuttings are formed.

[Ill.u.s.tration: Fig. 2466.]

Fig. 2466 represents a pipe cutter in which a cutting tool is employed, being fed to its cut by the handle which is threaded similar to the handle shown in Fig. 2464. The end jaw is operated to suit different diameters of pipe by means of the milled nut shown, which receives a threaded stem on the adjustable jaw.

[Ill.u.s.tration: Fig. 2467.]

PIPE VICE.--The ordinary bench vice is sometimes provided with an attachment to enable it to grip pipe at three points, and, therefore, hold it sufficiently firmly without squeezing it oval, but it is preferable to use a proper pipe vice, such as shown in Fig. 2467, which consists of a base frame bolted to the work bench and receiving a serrated die to grip the pipe. The upper die is carried to a frame pivoted on both sides to the base, and is operated to grip or release the pipes by means of the handled screw shown.

[Ill.u.s.tration: Fig. 2468.]

To change the dies one pivot is removed and the upper frame swung open, as in Fig. 2468.

[Ill.u.s.tration: Fig. 2469.]

The proper shape for pipe tongs depends upon the number of sizes of pipe the tongs are intended for, but in all cases the point at which the gripping point should be is about as shown in Fig. 2469. This enables the edge at A to enter the work and grip it. If this point of contact were nearer to C it would be apt to slip upon the pipe, whereas, were it farther towards B, it would present a less acute angle to the pipe, which would be apt to jam in the tongs.

It is obvious that, if the tongs be moved in the direction of H, the whole power applied to F acts to cause the edge at A to grip the pipe, and that the length from A to G has an important bearing on the grip of A to the pipe; because the nearer A is to G not only the greater the leverage of the leg F, but also the less A, with a given amount of movement of F on its pivot, endeavors to enter the pipe; hence the movement of A in a direction to grip the pipe is less in proportion to the movement of F, and has a corresponding increase of force. It follows then that the nearer the grip of A is to C, the less, and the nearer the grip to B the greater, its grip upon the pipe. But, by making the length of A such as to grip the pipe in about the position shown in the cut, there is lat.i.tude enough in the location at which it will grip the pipe to permit of the tongs being used upon pipe of a somewhat greater or less external diameter, increasing the availability of the tongs.

Furthermore, if A gripped the pipe at or too near to B, it would be apt to indent it. The crown of the jaw D may be made to fit to the pipe or to be clear of it; for thin pipe, as solid drawn bra.s.s pipe, it should fit so that the pressure will not indent the pipe, but for strong iron pipe it is better to let it clear, which will not only afford a firmer grip, but will also better fit the tongs to take in different diameters of pipe. In some cases, as in adjustable pipe tongs, the jaw surface D is, for this purpose, considerably [V]-shaped, as will be seen presently.

It is obvious that as A grips the pipe automatically, the tongs may be moved through any portion of a rotation that the location may render most desirable. Pipe tongs are designated for size by the diameter of the pipe they are intended for; thus, a pair of inch tongs are suitable for pipe an inch in diameter of bore, the handles or legs of the tongs coming so close together that both can be readily grasped in one hand applied at their extreme ends. If, however, the tongs be applied to pipe of a larger diameter the legs will be wider apart, and one hand will be required to be applied to each leg to force them together. A complete set of pipe tongs, therefore, includes as many pairs as there are diameters of pipe, unless adjustable tongs be used.

[Ill.u.s.tration: Fig. 2470.]

[Ill.u.s.tration: Fig. 2471.]

[Ill.u.s.tration: Fig. 2472.]

Adjustable tongs are made of various forms; thus a simple plan is shown in Fig. 2470. The gripping surface of the jaw is shaped as at V, so as to admit varying diameters of pipe, the smaller diameters pa.s.sing farther up the V, the distance of the end A of jaw, or leg F, being regulated to grip the pipe in the proper place by operating the screw S, which is tapped into the jaw F and pivoted in B, the slot C enabling F to move along B. The capacity of tongs of this design is about three diameters of pipe, as 1, 1-1/4, and 1-1/2 inches. There are various other forms of adjustable pipe tongs, but most of them possess the disadvantage that the adjustable jaw hangs loosely, involving some extra trouble in placing them upon the pipe, because one hand must be employed to guide the loose jaw and adjust its position on the pipe. Fig. 2471 represents tongs of this cla.s.s, the gripping size being varied by moving the jaw A upon B at the various notches. The end of B is serrated to afford a firmer grip upon the pipe. Fig. 2472 represents another adjustable pipe tongs, which is made in two parts, a straight lever A and hooked lever B, the former pa.s.sing through a slot in the latter. The back of the straight lever is notched and a serrated fulcrum piece C is pivoted in the slotted lever by a pin upon which the lever B receives its support when the tongs are in operation. The fulcrum piece is provided with a spring which retains the serrated edge in proper position to engage the notches in the lever A. By means of the thumb piece D, the piece C can be moved in either direction to increase or diminish the gripping size of the tongs. When the tongs are open the lever A can be moved within the slot and adjusted so that the tongs will fit the pipe. The fulcrum piece C, being pivoted, allows the full length of its serrated edge to come into contact with the corresponding portion of the lever A, so that the parts always have a firm bearing and are subjected to an equal wear.

A common form of pipe tongs of this cla.s.s is shown in Fig. 2473, B being pivoted to A by a pin, and changing to various holes in A to suit different diameters of pipe.

ERECTING PIPE WORK.--In erecting pipe work care must be taken to have it align as true as possible, as well as to have the joints tight enough to stand the required pressure without leakage. If the elbows, tees, or other fittings are not threaded true, a pipe whose thread is not true with its axis may be selected or cut purposely to suit the error in the fitting, so as not to leave an unsightly finish to the job.

[Ill.u.s.tration: Fig. 2471.]

[Ill.u.s.tration: Fig. 2474.]

Suppose, for example, that in Fig. 2474, _e_ is a pipe erected parallel to the wall, but that the holes in its elbows are tapped at an acute instead of at a right angle, then by cutting the thread on the end of pipe _d_ untrue with its axis, its far end will rotate out of true as denoted by the shaded and by the plain lines, and all that will be necessary is to screw up the pipe sufficiently firm to make the joint, but to leave it in the position shown in the plain lines.

If the pipe tightens sufficiently before it has reached that position it may generally be eased by rotating it back and forth in the elbow with the pipe tongs. If this does not suffice, the pipe must of course be threaded sufficiently further along. To cut a pipe out of true to suit an untrue elbow, a very good plan is to cut the end of the pipe at an angle to its axis, which will cause the dies to cant over when starting the thread, but little practice being required to educate the judgment as to how much to do this to suit any given degree of error.

In erecting pipe it is best to begin at one end and screw each successive piece firmly home to its place before attaching another, so that the lengths of the pieces may be accurate and not vitiated by s.c.r.e.w.i.n.g them up and causing them to enter farther into the fittings. If it is probable that the piping may have to be taken down after erection, it should be put up at first screwed together rather tighter than will be necessary, as the thread fits become eased by being moved one within the other. This is especially the case with bra.s.s fittings, upon which it is best in cutting the lengths of pipe to have it of full length, as the threads will conform to each other sufficiently to cause the pipe to enter a thread or so farther if the pipe be rotated back and forth a few times in the fitting.

The fit should in all cases be made by tightness of thread fit, and not by the union or elbow face jambing against the end of the thread or the pipe, as joints in which this is the case will usually leak if used under pressure.

The thread of both the pipe and the fitting should be smeared with a thick lead paint. If the pipe is to be used as soon as erected, plain red lead and boiled oil should be used for the paint; but if it may stand a few days it is better to mix white and red lead in about equal quant.i.ties, as this, if given time to dry, makes a tighter job. The quant.i.ty of this paint should not be more than will thinly cover the threads, otherwise it will squeeze out when the pipes are screwed home, and falling from the end of the pipe within the fitting be apt to be carried by the steam or water to the valves, and getting between them and their seats cause them to leak. The iron cuttings should be carefully cleaned both from the pipe and the fitting for the same reason.

In cases where the piping may require to be used under heavy pressure as soon as erected, it is a good plan to use dry red lead in varnish, thoroughly hammering it to mix it well, and thinning it after it has been so hammered.

In case of emergency a loose pipe may be somewhat improved by wrapping around its thread a piece of lamp wick saturated with this varnish lead, beginning at the end of the pipe and wrapping the thread from end to end.

It is preferable that the stem of the valve stand nearly horizontal, so that any water of condensation may pa.s.s freely away with the steam and not collect and lie in the pipe as it does when vertical. If it be quite horizontal the water of condensation will drip through the stuffing box; hence it is better that it stand 10 or 12 degrees from the horizontal.

It is better in all cases to purchase nipples than to make them by hand, because when made in a machine the threads are more true to the axis than those made by hand; especially is this the case in short nipples in which there is not sufficient length to use the guide socket when engaged in threading the nipple with the hand dies.

It is a very good plan in making such short nipples to cut them off the end of a length of pipe that has been threaded by machine, and to screw on the threaded end a coupling. Into this coupling a piece of pipe may be threaded to afford a hold in the vice. If then the nipple is long enough, a guide to suit the size of the nipple may be used in the threading dies, or a guide socket to fit the diameter of the coupling may be used.

A globe valve should be so placed on the pipe that the pressure will, when the valve is closed, fall on the bottom face of the valve, so that the steam may be shut off while the valve stem is being packed.

Cotton lamp wick plaited to fit the packing s.p.a.ce, and well oiled, is as good as anything to pack the stem with.

In taking old pipe down a refractory joint may be sometimes loosened by striking it with a hammer while it is under full pipe tongs pressure; or these means failing, the elbow or tee may be heated, which should be done as quickly as possible, so that the fitting may be hotter than the pipe. A very good method of doing this, where it is desired to save the fitting, is to pour red-hot lead over the fitting.

If it is not important to save the fitting, it may be split by a flat chisel, or by cutting a groove along it with a narrow cape chisel; or if the pipe is free the elbow may be rested on an anvil and hammered around its circ.u.mference, which will either free it or break it, if of cast iron.

When pipes are to be taken down and re-erected elsewhere they should all be marked to their fittings and places before being taken down, as this will preserve their lengths as near as possible for re-erection. Black j.a.pan is an excellent marking for this purpose because it dries quickly.

RE-FITTING THE LEAKY PLUGS AND BARRELS OF c.o.c.kS.--When a c.o.c.k leaks, be it large or small, it should be refitted as follows, which will take less time than it would to ream or bore out the c.o.c.k or to turn the plug, unless the latter be very much worn indeed, while in either case the plug will last much longer if refitted, as hereinafter directed, because less metal will be taken off it in the re-fitting.

After removing the plug from the c.o.c.k, remove the scale or dirt which will sometimes be found on the larger end, and lightly draw-file, with a smooth file, the plug all over from end to end. If there is a shoulder worn by the c.o.c.k at the large end of the plug, file the shoulder off even and level. Then carefully clean out the inside of the c.o.c.k, and apply a very light coat of red marking to the plug, and putting it into the c.o.c.k press it firmly to its seat, moving it back and forth part of a revolution; then, while it is firmly home to its seat, take hold of the handle end of the plug, and pressing it back and forth at a right angle to its length note if the front or back end moves in the c.o.c.k; if it moves at the front or large end, it shows that the plug is binding at the small end, while if it moves at the back or small end, it demonstrates that it binds at the front or large end. In either case the amount of movement is a guide as to the quant.i.ty of metal to be taken off the plug at the requisite end to make it fit the c.o.c.k along the whole length of its taper bore.

If the plug shows a good deal of movement when tested as above, it will be economical to take it to a lathe, and, being careful to set the taper as required, take a light cut over it. Supposing, however, there is no lathe at hand, or that it is required to do the job by hand, which is, in a majority of cases, the best method, the end of the c.o.c.k bearing against the plug must be smooth-filed, first moving the file round the circ.u.mference, and then draw-filing; taking care to take most off at that end of the plug, and less and less as the other end of the plug is approached. The plug should then be tried in the c.o.c.k again, according to the instructions already given, and the filing and testing process continued until the plug fits perfectly in the c.o.c.k. In trying the plug to the c.o.c.k, it will not do to revolve the plug continuously in one direction, for that would cut rings in both the c.o.c.k and the plug, and spoil the job; the proper plan is to move the plug back and forth at the same time that it is being slowly revolved. As soon as the plug fits the c.o.c.k from end to end, we may test the c.o.c.k to see if it is oval or out of round. The manner of testing the c.o.c.k is as follows:--

First give it a very light coat of red marking, just sufficient, in fact, to well dull the surface, and then insert the plug, press it firmly home, and revolve it as above directed, then remove the plug, and where the plug has been bearing against the surface of the c.o.c.k the latter will appear bright. If, then, the bore of the c.o.c.k appears to be much oval, which will be the case if the amount of surface appearing bright is small, and on opposite sides of the diameter of the bore, those bright spots may be removed with a half-round sc.r.a.per.

Having eased off the high spots as much as deemed sufficient, the c.o.c.k should be carefully cleaned out (for if any metal sc.r.a.pings remain they will cut grooves in the plug), and the red marking re-applied, after which the plug may be again applied. If the plug has required much sc.r.a.ping, it will pay to take a half-round smooth file that is well rounding lengthwise of its half-round side, so that it will only bear upon the particular teeth required to cut, and selecting the highest spot on the file, by looking down its length, apply that spot to the part of the bore of the c.o.c.k that has been sc.r.a.ped, draw-filing it sufficient to nearly efface the sc.r.a.per marks. The process of sc.r.a.ping and draw-filing should be continued until the c.o.c.k shows that it bears about evenly all over its bore, when both the plug and the c.o.c.k will be ready for grinding.

Here, however, it may be as well to remark that in the case of large c.o.c.ks we may save a little time and insure a good fit by pursuing the following course, and for the given reasons. If a barrel bears all around its water-way only for a distance equal to about 1/16th of the circ.u.mference of the bore, and the plug is true, the c.o.c.k will be tight, the objection being that it has an insufficiency of wearing surface. It will, however, in such case wear better as the wearing proceeds. Plug and barrel being fitted as directed, we may take a smooth file and ease away very lightly all parts of the barrel save and except to within, say, 3/8 inch around the water or steam-way. The amount taken off must be very small indeed, just sufficient, in fact to ease it from bearing hard against the plug, and the result will be that the grinding will bed the barrel all over to the plug, and insure that the metal around the water or steam-way on the barrel shall be a good fit, and hence that the c.o.c.k be tight.

The best material to use for the grinding apparatus is the red burnt sand from the core of a bra.s.s casting, which should be sifted through fine gauze and riddled on the work from a box made of, say, a piece of 1-1/2 pipe 4 inches long, closed at one end and having fine gauze instead of a lid.

A very good material, however, is Bath brick rubbed to a powder on a piece of clean board. Neither emery nor ground gla.s.s is a good material, because they cut too freely and coa.r.s.ely, which is unnecessary if the plug has been well fitted.

Both the barrel and the plug should be wiped clean and free from filings, &c., before the sand is applied; the inside of the barrel should be wetted in and the plug dipped in water, the sand being sifted a light coat evenly over the barrel and the plug. The plug must then be inserted in the barrel without being revolved at all till it is home to its seat, when it should be pressed firmly home, and operated back and forth while being slowly revolved. It should also be occasionally taken a little way out from the barrel and immediately pressed back to its seat and revolved as before, which will spread the sand evenly over the surfaces and prevent it from cutting rings in either the barrel or the plug. This process of grinding may be repeated, with fresh applications of sand, several times, when the sand may be washed clean from the barrel and the plug, both of them wiped comparatively dry and clean, and the plug be re-inserted in the barrel, and revolved, as before, a few revolutions; then take it out, wipe it dry, re-insert and revolve it again, after which an examination of the barrel and plug will disclose how closely they fit together, the parts that bind the hardest being of the deepest colour. If, after the test made subsequent to the first grinding operation, the plug does not show to be a good even fit, it will pay to ease away the high parts with a smooth file, and repeat afterwards the grinding and testing operation.

To finish the grinding, we proceed as follows: Give the plug a light coat of sand and water, press it firmly to its seat and move it back and forth while revolving it, lift it out a little to its seat at about every fourth movement, and when the sand has ground down and worked out, remove the plug, and smear over it evenly with the fingers, the ground sand that has acc.u.mulated on the ends of the plug and barrel, then replace it in the barrel and revolve as before until the plug moves smoothly in the barrel, bearing in mind that if at any time the plug, while being revolved in the barrel, makes a jarring or grating sound, it is cutting or abrading from being too dry. Finally, wipe both the barrel and the plug clean and dry, and revolve as before until the surfaces a.s.sume a rich brown, smooth and glossy, showing very plainly the exact nature of the fit. Then apply a little tallow, and the job is complete and perfect.

In place of the tallow a soft paste of good beeswax and castor oil is an excellent application, the two being heated in order to thoroughly mix them.

The grinding material must be frequently changed to produce smooth work, because if the grinding cuttings acc.u.mulate in it, they will scratch and score the work. Indeed, it is a good plan when convenient, to hold the c.o.c.k and plug under water while grinding them, and to occasionally lift the plug out, so as to wash out the cuttings.

The surface of a well-ground plug will be in all cases polished, and not have that frosted appearance which exists so long as active grinding is proceeding, and all that is necessary to produce this polish is to well work the plug in its barrel while keeping it quite clean.