Fig. 2454.
Joints for Boiler Fittings.—Let it be assumed that the casting shown in [Figs. 2453] and [2454] requires to be fitted to a boiler, both being new. In this case, the holes for the studs or bolts should first be drilled in the flange of the casting, which will reduce its weight and render it easier to handle. The casting should then be held against the boiler in its proper position and location; and, with a fork scriber whose width of points is equal to the widest space between the face of the casting flange and the boiler, pass the fork scriber around the fitting or casting with one point against the boiler shell and the other pressed against the edge of the casting, the result being to mark around the flange of the latter a line exactly following the surface or contour of the boiler, and at a distance from the boiler the nearest that will suffice to properly bed the casting to the boiler surface, or, in other words, the line that will exactly mark the amount of metal requiring to be cut off the flange face to make it bed all over; and that face may, therefore, be cut down to the line. In chipping and filing it, however, the straight-edge may be used to advantage as follows:—
Fig. 2455.
Suppose the casting flange to be gripped in the vice facing the operator, as in [Fig. 2455], and that l l represents the scribed line: then the cape chisel cuts may be carried clear across the flange, coming exactly down to the line on each side of the flange, while a straight-edge s may be used as shown to show when the cut is carried across level. Then, when the intermediate spaces are cut out with the flat chisel the surface will be of correct shape, and the surface may be rough filed. The casting should be cut clear down to the lines, and if the job has been properly set, marked and faced, no further trying will be necessary previous to marking the bolt or stud holes in the boiler. It is well, however, if the operator is inexperienced in this kind of work, to again set the casting in its proper position to correct the fit. But, with proper care, all the holes in the boiler may be marked without any second fitting of the flange, since the operation properly performed is bound to give correct results. In doing a job of this kind it must be borne in mind that it is very easy to consume more time in trying and altering the job than is required under proper conditions to do the entire job; hence, in setting the casting, preparatory to marking it with the fork scriber, nothing is near enough that does not carry with it a conviction of perfect reliability; and if any doubt exists it is better to go through the process again. If the casting flange varies much in shape from its seat, and rocks or is unsteady, wooden wedges may be placed beneath it, or a few pellets of stiffly mixed red lead may be placed on the boiler where there is most room between it and the casting, the boiler surface being coated or painted with red marking, so that the pellets shall adhere to it and not to the flange face. If the casting is too heavy to be steadied by hand, one hole may be drilled in the boiler and a temporary bolt inserted to hold the casting while setting it in position, and marking with the fork scriber.
When the flange is approaching a fit, it must be placed in position on the boiler and the stud holes marked on the boiler with an ordinary scriber, its point being pressed against the boiler while it is pressed against the side of the hole in the casting flange and traversed around it, so as to scribe on the boiler surface circles corresponding to the holes in the flange. From the centres of these circles others of the proper size of the tapping holes may be struck and the tapping holes may then be drilled, and the studs put in. The remainder of the fitting operation consists in applying red marking on the boiler surface, bolting the casting to its place and filing the high spots. The marking is made to show plainly upon the flange by light hammer blows with a piece of wood interposed between the hammer and the flange face to prevent piercing the latter. These blows, however, should be lightly delivered, or they will cause the marking to be deceptive.
