Sometimes, even with the greatest care, a cap-screw or stud will break off in the hole. To remove the broken piece is often very difficult and sometimes it is absolutely necessary to rebore and thread the hole. Many times, however, the stub may be unscrewed by boring a hole in it and tapping with a left-handed thread of smaller size. By screwing a left-handed screw into this and setting up tight the tendency will be to unscrew the right-hand thread on the broken stub. Many times a bolt or screw thread becomes badly worn or rusted and the bolt or nut will not hold. Usually it is always best

Fig. 139. Tightening Old Bolt

to retap the hole and use a new bolt, but in many cases such methods are impossible. At such times the thread may be made to hold like new by slitting the end of the bolt or screw and spreading the sides slightly, or in the case of large bolts by driving in a small wedge (Fig. 139). If the nut is worn and the bolt is all right, the former may be made tight by heating to red heat and then sprinkling cold water around the outer side. This will shrink the nut considerably and result in a snug fit. The application of heat for expanding metal is often very useful, and many joints can be taken apart or put together when hot that cannot be started when cold.

Loose sprockets, cams, wheels, etc., can all be made very tight by expanding the pieces with heat and while still hot putting them together and allowing them to shrink to a close fit. Sometimes a nut which is not held by a lock washer or cotter pin may become loose and give considerable trouble. This may be easily overcome by sawing a little less than half-way through the nut and then springing the two parts close together. A nut treated in this way will hold like a lock nut and will

Fig. 140.-Slit Locknut

never loosen (Fig. 140). Care should be taken, however, not to cut the slit too deep or too wide, or the threads will be stripped in screwing it on.

Very often one requires a pipe-fitting of a smaller or larger size and has no reducer or bushing at hand. At such times the man provided with pipe taps and dies may make excellent reducers by using short pieces of standard brass pipe. In brass pipe each size will thread inside for the next smaller size: thus 4-inch pipe may be threaded for 1/8; 3/8 for 1/4; 1/2 for 3/8; 3/4 for 1/2; 1-inch for 3/4, etc. Iron pipe will not thread so accurately, but in many cases a thread can be cut in iron pipe that will answer for an emergency. Pipecouplings may also be used as reducers by threading the outside for the next larger sized fitting, but they are harder to handle and do not make as good reducers as the pieces of brass pipe.

In threading brass rods it will often be found that the same sized die as the nut used will not allow the nut to be screwed on. In such cases the rod should be slightly filed down or rubbed with emery before threading. Brass has a tendency to bind when it fits tightly, and threads on brass can always be made with more play than on iron. In using 1/4-inch machine thread nuts it is often advisable to use a No. 14 thread with the same pitch in threading bars for the nut.

If you should require a pipe wrench and have none at

hand you can often handle a pipe successfully by placing a three-cornered file in a monkey wrench and using this on the pipe (see Fig. 141). Old files that are clogged and dull may be readily cleaned and made as good as new by soaking for a short time in sulphuric acid and water. The solution should be weak-about 1 ounce of acid to 2 quarts of water-and after soaking a few hours the

files should be washed thoroughly in a strong soda solution, brushed off clean, and dried by heat and then oiled.

In plugging old holes with bolts or pipe plugs there is often great difficulty in getting them to hold tightly and not leak. This is often the case in holes tapped in water jackets where the metal around the hole has rusted away until so thin that it will not hold the thread. Such holes may be covered by brazing on a piece of metal or by fastening a patch of metal over the hole by means of several small screws and a packing between the jacket and the patch. The former requires a professional brazer, while the latter takes considerable time, and if the jacket is rusted badly you may find several holes to plug instead of one covered up. A very good method under such conditions is to file the hole oblong or oval, as shown in Fig. 142, A. Then cut a piece of stiff brass or soft steel or iron just large enough to slip into the hole (Fig. 142, B). Bore a hole through the centre of this piece and fasten it on the end of a short bolt or screw by threading and rivetting (Fig. 142, C). Thread the bolt or screw on the other end almost to the piece of metal. Slip the metal piece into the hole and turn around so that the long ends are across the short diameter of the hole. Put a piece of packing over the projecting bolt (Fig. 142, D), place an iron or brass patch over the packing (Fig. 142, E), and screw the whole down firmly against the outside of the jacket by a nut on the threaded bolt as illustrated in Fig. 142, and it will be found a most satisfactory way to stop up old holes or leaks in many places. If the cylinder is a small

one the inner piece of metal, or yoke, as well as the outer patch, must be bent or filed to a curve to fit the jacket; but in large cylinders the curve is so slight that only the outer patch need be curved. The only danger in using this method lies in setting up the nut too tight and thus cracking or breaking the metal around the hole.

Small cracks or leaks in cylinders or jackets may often be stopped by filling with a strong solution of

sal ammoniac and water until well rusted up. In large holes or leaks a better method is to fill the opening with a cement of some sort. Various cements are made to withstand heat, water, and oil in iron or metal, but either of the following will prove excellent and may also be used to advantage in fitting pipe-joints where a permanent connection is desired or in placing under