Modern Machine-Shop Practice Part 206

Now, when the staves are cut out it is necessary to have some kind of a frame or support to hold them while jointing them; hence, draw also from the points of division, as D, E, F, the lines _a_, _b_, _c_, _d_, _e_, _f_, and these will form the sides of a half-disk polygon, whose diameter is from D to F. A sufficient number of these polygonal half-disks are cut out to stand about two feet apart along the whole length of the pipe, as in Fig. 2794, and on these, temporarily fastened to the board B, the staves are jointed and fastened together by glue while each stave is held to its place on each half-disk by a screw. The top stave may be put on first, as it will act as a stay to the half-disks. If the pipe is so long that it is composed of more than two pieces, the end pieces should be put on first, and the intervening s.p.a.ce filled up last, which enables the ends to abut firmly. The second half may be added to the first one, putting a piece of paper between the edges of the two to prevent their sticking together.

If the pipe has a bend, it is built up separately, instead of being formed of staves, the process being as follows:--

[Ill.u.s.tration: Fig. 2795.]

[Ill.u.s.tration: Fig. 2796.]

In Fig. 2795 let B represent the centre of the bend curve, the line C representing one end, G the other end, H the inner and J the outer arc of the bend. Let it be determined to build up the bend in five pieces, as shown at 1, 2, 3, 4, 5, which represents an end view of the half pattern. Templates are then made for each of the pieces 1, 2, &c., being formed as denoted by the oblique lines, whose dimensions slightly exceed the half circle E of the pattern, to allow wood for dressing up. To find the curve for these pieces, set the compa.s.ses to a radius from B to the outer corner of piece 1, and draw the arc K. Set the compa.s.ses to the radius from B to the inner corner of piece 1, and draw the arc L, and the s.p.a.ce between these two arcs, which s.p.a.ce is marked 1 T, is a template for the curve of piece 1. By a similar process applied to pieces 2, 3, 4 and 5 similar templates for their respective curves are obtained; and selecting timber of a proper thickness, we mark out the respective curves from these templates, which may be of thin board or of stiff paper. In putting these pieces together the lower ones are set to lines forming a plan of the bend, being set a little outside the lines to allow wood for truing the pieces to shape after they are put together. The lower pieces are temporarily fixed to the board on which the plan is marked, and the upper ones fastened to the lower by glue, the joint surfaces of each line being planed true previous to being glued. It is a great a.s.sistance, however, to cut out two half circles, representing the ends of the pipe, and to place them on the board to build upon. When a bend of this kind occurs in a covering for a pipe that is exposed to view, it is necessary, for the sake of appearance, to have the pieces composing the bend to correspond with those on the straight part of the pipe, as shown in Fig. 2796. The part A would be got out in staves, as described for the pattern of a pipe. The bend B would be also got out as described for that figure for a bend, save that the number of staves for the bend would equal the number on the pipe.

But in this case each stave should be fitted to its fellow by pins, or its edge fitting into dowels on the edge of its fellow; thus one edge of a stave would have the dowels and the other the pins; the whole, when finished, being bound together by metal bands, as shown in the figure.

[Ill.u.s.tration: Fig. 2797.]

The patterns for a globe valve, such as shown in section in Fig. 2797, would be made as follows (which is taken from "The Pattern Makers'

a.s.sistant"):--

[Ill.u.s.tration: Fig. 2798.]

[Ill.u.s.tration: Fig. 2799.]

"The f.l.a.n.g.es vary in shape; but as a rule small valves are provided with hexagons and large ones with round f.l.a.n.g.es suitable for bolting to similar f.l.a.n.g.es to make joints. For small valves, say up to 2 inches, the pattern is usually made with the hexagons cut out of the solid, but for sizes above that, they should be made in separate pieces, as shown in Fig. 2798, and screwed to the pattern, so that in case of necessity they may be removed, and f.l.a.n.g.es subst.i.tuted in their stead. In Fig.

2799, we have a perspective view of the finished pattern; and Fig. 2800 represents the pattern as prepared, ready to receive a f.l.a.n.g.e or hexagon as may be required. A globe valve pattern should be made in halves, as shown in Fig. 2801, the parting line of the two halves being denoted by A B. To make this pattern, we first prepare two pieces of wood so large that, when pegged together, the ball or body of the pattern can be turned out of them, and long enough not only to reach from P to P, in Fig. 2799, but also to allow an excess by means of which the two pieces may be glued or otherwise fixed together. These two pieces we plane to an equal thickness, and then peg them to retain them in a fixed position, taking care, however, that the pegs do not occur where the screws to hold the f.l.a.n.g.es will require to be. We also place two pegs within a short distance of what will be the ends of the pattern when the excess in length referred to is turned off. We next prepare, in the same way, two more pieces, to form the two halves of the branch, shown at B, in Fig. 2801, for which, however, one peg only will be necessary. These pieces must be somewhat wider than the size of the required hexagon across the corners, that is, supposing the hexagon is to be solid with the branch; otherwise we must make them a little wider than the diameter of the hub of the f.l.a.n.g.e, or of the round part of the hexagonal pieces.

Their lengths must be such as to afford a good portion to be let into the ball or body of the pattern (as shown by the dotted lines in Fig.

2800), which is necessary to give sufficient strength. The two pieces must be firmly fixed together, and then turned in the lathe.

[Ill.u.s.tration: Fig. 2800.]

[Ill.u.s.tration: Fig. 2801.]

[Ill.u.s.tration: Fig. 2802.]

"During the early stages of the turning, or, in other words, during the roughing out, we must occasionally stop the lathe and examine the flat places on the body; for unless these places disappear evenly, the work is not true, and one half will be thicker than the other, so that the joint of the pattern will not be in the middle. It was to insure this that the pieces were directed to be planed of equal thickness, since, if such is the case, and the flat sides disappear equally and simultaneously during the turning, the joint or parting of the pattern is sure to be central. If the lathe centres are not exactly true in the joint of the two pieces, they may be made so by tapping the work on the side having the narrowest flat place, the process being continued and the work being trued with the turning tool at each trial until the flat places become equal. By this means, we insure, without much trouble, two exact halves in the pattern, which is very important in a globe valve pattern on account of the branch and other parts, not to mention the moulding. Having turned the body of the pattern to the requisite outline, and made, while in the lathe, a fine line around the centre of the ball where the centre of the branch is to come, as shown in Fig.

2800 by the line A, we make a p.r.i.c.k point (with a scriber) at each crossing of the line A and the joint or parting of the pattern. We then mount the body upon a lathe chuck, in the manner shown in Fig. 2802. A point centre should be placed in the lathe and should come exactly even with the line A. In Fig. 2802, V V are two [V]-blocks made to receive the core prints. These [V]s are screwed to the lathe chuck, and the pattern is held to them by two thin straps of iron, placed over the core prints and fastened to the [V]s by screws. If the chuck and centre point run true, the [V]-blocks are of equal height, and the core prints are equal in diameter, the p.r.i.c.k point opposite to the one placed to the centre point will run quite true; and we may face off the ball or body to the required diameter of branch, and bore the recess to receive the same. We make the holes in the f.l.a.n.g.es of the same size as the core prints; but we should not check in the print, because, if a f.l.a.n.g.e with a different length of hub were subst.i.tuted, it would be a disadvantage.

To obtain the half f.l.a.n.g.es, we take a chuck and face it off true in the lathe; then, with a fine scriber point, we mark the centre while the chuck is revolving. We then stop the lathe, and, placing a straight-edge to intersect the chuck centre, we draw a straight line across the chuck face. We then take two pieces suitable for the half f.l.a.n.g.es, and plane up one flat side and one edge of each piece. If the f.l.a.n.g.es are not large ones, they may be planed all at once in a long strip. We place the pieces in pairs, and mark on each pair a circle a little larger than the required finished size of f.l.a.n.g.e. We then fix each pair to the chuck, with the planed faces against the chuck, and the planed edges placed in contact, their joint coming exactly even with the straight line marked on the chuck face, and we may then turn them as though they were made in one piece and to the requisite size.

[Ill.u.s.tration: Fig. 2803.]

"In Fig. 2803 we have a representation of one half of a suitable core box, the other half being exactly the same, with the exception that the position of the internal part.i.tion is reversed. To get out this core box, we plane up two pieces of exactly the same size and length as the pattern, and of such width and thickness as will give sufficient strength around the sphere, allowing s.p.a.ce for the third opening. After pegging these two pieces together, we gauge, on the joint face of each, lines representing the centres of the openings and the centre of the sphere. We then chuck them (separately) in the lathe, and turn out the half sphere. We next place the two halves together, and chuck the block so formed in the three positions necessary to bore out the openings; or if preferred, we may pare them out. The part.i.tion (A, in Fig. 2803) follows the roundness of the centre hole, and is on that account more difficult to extract from the core than if it were straight and vertical. When, however, the part.i.tions are of this curved form, the pieces of which they are formed are composed of metal, bra.s.s being generally preferred. Patterns have in this case to be made wherefrom to cast these pieces, and they may be made as follows: First, two half pieces are turned; each is then cut away so as to leave the shape as shown at A in the same figure, and is then fitted into the spherical recess in the core box, letting each down until both are nearly but not quite level. The two wing pieces are then fastened on, and this pattern is complete. When the pieces are cast, they must be filed to fit the core box, and finished off level with its joint face, a small hole being drilled in the centre, and a pin being driven through the piece and into the box to steady the corners. We then saw the pieces in halves with a very fine saw.

[Ill.u.s.tration: Fig. 2804.]

"If the part.i.tion, instead of following the roundness of the valve seat, is made straight, the construction of the core box is much more simple.

In this case, a zigzag mortice is made clear through each half of the box, its size and shape being that of the required part.i.tion. Fig. 2804 represents a half-core box of this kind. A piece of wood A is fixed, as shown, to the part.i.tion, to enable the core maker to draw it out before removing the core from the box. The mortice for the part.i.tion should be turned out before the half-spherical recess, the mortice being temporarily plugged with wood to render easy the operation of turning.

[Ill.u.s.tration: Fig. 2805.]

"In very large valves (say 10 or 12 inches) a half-core box is generally made to serve by fitting the two half part.i.tions, shown at A, in Fig.

2803, to a half-core box, and keeping them in position by means of pegs, a half-core being made first with one and then one with the other in the core box. It is often necessary to form a raised seat in the body of an angle valve, such as shown in Fig. 2805, which represents a section of such a body. It is shown with f.l.a.n.g.ed openings, though in small valves hexagons to receive a wrench would be subst.i.tuted.

[Ill.u.s.tration: Fig. 2806.]

[Ill.u.s.tration: Fig. 2807.]

"Fig. 2806 is a plan of half the core box necessary for forming the raised seat. From this construction, it will be seen that the large core, though solid with the branch core, is not solid with that forming the hole in the seat and the part below it; therefore the core prints on the body pattern must be left extra long to give sufficient support in the mould for the overhanging cores. The loose round plug P, is made of the size of the outside of the seat and fitted to the box. The part outside the box is a roughly shaped handle to draw it out by. The diminished part D is a print, and into the impression left by it is inserted the core made in box shown in Fig. 2807. The print D is of the same diameter as the hole in the seat; and the print on the pattern is of the size of the increased diameter below the seat. Large angle valves are made with half a core box by making a branch opening in the box right and left, a semicircular plug being provided. Two half-cores are made with the plug, first in one and then in the other branch opening.

The plug P should be in this case only half round."

[Ill.u.s.tration: Fig. 2808.]

For finding the lengths of the sides of regular polygons, scales, such as shown in Figs. 2808 and 2809, may be used, the construction being as follows:--

[Ill.u.s.tration: Fig. 2809.]

Draw a horizontal line O P, Fig. 2809, and at a right angle to it the line O B. Divide these two into inches and eighths of an inch, and draw lines meeting the corresponding divisions on O P, O B. From the point O draw the following lines: A line at 55-1/2 degrees from line O P, which is to serve for polygons having 9 sides; a line at 52-1/2 degrees to serve for polygons having 8 sides; a line at 49 degrees for polygons having 7 sides; a line at 45 degrees for 6 sides; a line at 40 degrees for polygons having 5 sides. It may be added, however, that additional lines may be drawn at the requisite angle for any other number of sides.

The application of the scale is as follows:--

The point O represents the centre of the polygon; hence from O to the requisite line of division on O B represents the radius of the work.

From the line O B to the diagonal line (measured along the necessary horizontal line of division) is shown the length of a side of the polygon. From the point O, measured along the line having the requisite degrees of angle, to the horizontal line denoting the radius of the work, gives the diameter across corners of the polygon. The diameter across the flats of a square being given, its diameter across corners will be represented by the length of a line drawn from the necessary line of division on O B to the corresponding line of division on O P. A cylindrical body is to have six sides, its diameter being 2 inches, what will be the length of each side? Now, the radius of the 2-inch circle of the body is 1 inch; hence, find the figure 1 on line O B and measure along the corresponding horizontal line the distance from the 1 to the line of 45 degrees, as denoted by the thickened line.

A body has six sides, each side measuring an inch in length, what is its diameter across corners? Find a horizontal line that measures an inch from its intersection of the line O B to the line of 45 degrees, and along this latter to the point O is one-half the diameter across corners.

_Example 3._--It is desired to find the diameter across corners of a square whose side is to measure 3 inches. Measure the distance from the 3 on line O P to the 3 on line O B, which will give the required diameter across corners.

This scale lacks, however, one element, in that the diameter across the flats of a regular polygon being given, it will not give the diameter across the corners. This, however, we may obtain by a somewhat similar construction. Thus, in Fig. 2808, draw the line O B, and divide it into inches and parts of an inch. From these points of division draw horizontal lines; from the point O draw the following lines and at the following angles from the horizontal line O P:--

A line at 75 for polygons having 12 sides.

" 72 " 10 "

" 67-1/2 " 8 "

" 60 " 6 "

From the point O to the numerals denoting the radius of the polygon is the radius across the flats, while from point O to the horizontal line drawn from those numerals is the radius across corners of the polygon.

A hexagon measures 2 inches across the flats, what is its diameter measured across the corners? Now, from point O to the horizontal line marked 1 inch, measured along the line of 60 degrees, is 1-5/32 inches; hence the hexagon measures twice that, or 2-5/16 inches across corners.

The proof of the construction is shown in the figure, the hexagon and other polygons being marked for clearness of ill.u.s.tration.

[Ill.u.s.tration: Fig. 2810.]

[Ill.u.s.tration: Fig. 2811.]

Let it be required to make a pattern for a section of pipe such as shown in section and in plan in Fig. 2810, which is from "The Pattern Maker's a.s.sistant." This pattern would be made to mould, as shown in the section, lying horizontally, and must therefore be made in two halves, the line of joint for the two halves being along A B in Fig. 2811.

"The body A and the branch B would be made separate from the f.l.a.n.g.es, and would be reduced in diameter at the ends to receive them. To form A, take two pieces of timber, say three inches longer than the length of A, including the core prints, and measuring a little more than half the diameter of the pipe one way, and a little larger than the full diameter of the pipe the other way, and glue them together at the ends for a distance of 1-1/2 inches, which will serve to hold them while turning them in the lathe.

"The pieces may then be turned in the lathe to the required diameter.

During this turning, however, it is essential to insure that the joint of the two pieces be exactly in the centre, otherwise one half of the pattern will be (when the halves are separated) thicker than the other.

"The ends are then turned down to receive the f.l.a.n.g.es, the reduced diameter being necessary so as to leave a shoulder for the f.l.a.n.g.es to abut against to keep them true, or at a right angle to the axial line of the body. The branch is turned up in the same way, and the f.l.a.n.g.es are then turned and put on.

"The end of the branch may be cut to fit the circ.u.mference of the body as follows:--