MACHINE SHOPS — FRAMES AND CYLINDERS
— The frames come into the frame shop from the steel plate manufacturers, in whose works they are rolled in a similar manner to boiler plates. They are thicker than the latter, the usual thickness in British practice being from 1 in. to 1⅛ in. They arrive cut to a general all round size as shown by the outer rectangle in
Fig. 17, this size being the smallest possible to allow of the finished frame being cut out from it. The frame plates are first tried over for straightness, and then levelled and straightened by means of hydraulic jacks.
They are then marked off, and roughly punched out to shape by making a series of interlacing consecutive holes outside the marked lines as in Fig. 18, leaving about ¼ in to enable them to be machined to size. After being punched, the plates are heated in a furnace and annealed or cooled slowly to remove injury to the material caused by the punch. When cold they are slotted
to the exact size and shape required in a large slotting machine. All the machines in the frame shop are very large, the bed of the slotting machine being at least 50 ft. long, and the machine has three or four tools working at once. Eight or ten frames are placed one on top of the other, Fig. 18. — Punching the Outline of the Frame Plate
and all are slotted together at one operation, the top frame only having been marked off, and the proper outline drawn upon it. The next operation is to mark off and drill all the bolt and rivet holes, of which there will be from 300 to 400 according to the size and type of engine. The holes for bolts and cold rivets are drilled ¹⁄₁₆ in. less than the finished diameter, so that they can be reamered or “rose-bitted” out by the erectors when fitting up the cylinders, stays, and brackets to them. About four or five frames are drilled together in one batch, of which the top one is marked off, and this plate is afterwards used as a template or drilling “jig” when the later batches are drilled. In some railway works separate frame templates or jigs are used for standard classes of engines. These consist of plates about ¾ in. thick in which all the holes are drilled in their exact positions but larger than the holes in the frame. The holes in the template or “jig” are then bushed with steel bushes, the internal diameters of which are the exact diameters of the holes as drilled in the frame. This jig is placed on the top of the frames to be drilled, and the bushes act as guides for the drills. The drilling is done in multiple radial drilling machines, which may be either special machines or of the radial type shown in Fig. 3.
The drilling completed, the frames are placed upside down in a vertical position in screw jacks or trestles provided with arrangements for holding them in this position. All sharp edges are then removed and the corners of the recesses into which the hornblocks fit are rounded. The frames are again laid on their sides, the hornblocks are bedded down and fitted into the recesses slotted in the frames to receive them, and the various brackets are also bedded down to their proper places. The bolts which secure the hornblocks are turned to exact size, and must be driven in to be an absolutely tight fit. The main frames are then sent to the erecting shop, a pair being required for each engine. The bogie requires an additional pair of small frames. These together with the buffer beams of steel, cross-stays, etc., are dealt with in the frame shop in a similar manner to the frames themselves. The riveting together of the cross-stays and frames is always done in the erecting shop, only the plates themselves being treated in the frame shop.
Fig. 19. — Marking-Off Cylinders.
The cylinders are machined in a shop which contains a number of single and double boring machines, and also drilling and planing machines, all being tools of large size and most of them of special designs for locomotive work. The rough cylinder castings are lifted by a crane on to a large cast iron marking-off table, the surface of which is perfectly level. The casting is placed on planed blocks b
, Fig. 19, and its level is adjusted by wedges above them. Those parts on which lines are to be marked are painted with whiting to show the scriber marks,
which when made are marked with centre punch dots. Centre strips a
of thin iron are placed diametrically across the bores. The centres at both ends are found with compasses, and marked on the strips. The cylinders are then levelled by using a straight edge and spirit level across the centres, the necessary adjustments of level being
Fig. 20. — Marking-Off
Cylinder Port Faces.
made by the wedges. The centres are tested by the scribing block c
which has the underside of its foot a perfectly plane surface; the needle pointer of this is shown on the centre line, which is drawn by it all round the casting. All lines such as d
for surfaces which require planing are marked. Vertical centre and other vertical lines are drawn with the blade of a T-square having its broad edge on the table. The bore of the cylinder and all holes are drawn with compasses and centre popped. The dimensions are taken from the drawings, or in the case of standard engines will be measured from gauges specially made for the cylinders of different classes of engines. The whole work must be checked carefully to see that there is sufficient material on all surfaces for planing and boring to finished sizes.
The face into which the steam ports (s
Fig. 21. — Double Boring Machine for Cylinders.
By Craven Bros., Ltd. (Manchester).
exhaust ports (p
) Fig. 20, emerge must also be marked off, a template in which holes are cut for the ports being used for this purpose. The edges of the ports were formerly slotted out, but they are now generally milled out by a milling machine. It should be added that the cylinders shown in Fig. 19 are cast separately, the two halves being bolted together to form one pair. One of the flanges is shown at f
, Fig. 19, and in this case these flanges have also to be marked off for planing, the essential point being that the dimensions g, g
from the face of the finished flange to the centre of the cylinder on each side are exactly equal.
In many works much of the planing of the various outer surfaces is done first, using the scribed lines as a guide, and then the cylinders are set down on the bed of a boring machine on one of the planed surfaces and bored. The centre line of the bore of the cylinder is the datum line to which all other dimensions refer, and therefore some works consider it preferable to bore the cylinders before planing them. Fig. 21 shows a double boring machine for the purpose of boring two inside cylinders at once. The two heavy revolving boring bars are passed through the cylinders, the latter being bolted to the grooves in the bed of the machine. On each bar there is a disc carrying three cutting tools, and the two projecting arms carry tools for facing the ends of the cylinders, on to which the covers have to be fitted. Each cylinder is
Fig. 22 — Cylinder Boring and Drilling Machine.
By Messrs. William Asquith, Ltd. (Halifax).
bored to exact diameter, except at the two ends where the bore is slightly enlarged. These enlarged ends are termed the “counter-bores” and their object is to prevent a ridge being formed at the ends of the cylinder as the piston wears down the metal. The end flanges for the cylinder covers are also faced at the same time by the tools carried in the projecting arms. These flanged faces and the bores and counter bores can be seen in the pair of cylinders shown in Fig. 22. These cylinders have circular piston valves, and the boring of these is also done on a similar machine with smaller boring bars.
The planing of the various sides and flanges, and also of the steam chests port facings, when the latter have ordinary slide valves, may be done either on an ordinary large planing machine or on special machines made for the purpose. The cylinders have to be set on the machine by the bore to plane the top and bottom surfaces.
In those works in which the boring is done before the planing, one method is to use two standards which are splined underneath, the tongue or spline fitting into one of the grooves in the table of the planing machine. The top part of each standard is provided with a circular face plate which just fits into the counterbore of the bored cylinder. The standards are placed so that the face plates enter the counterbore at each end, and they are pulled up to grip the cylinders by means of a long central bar with nuts. The centre line of the bore is thus held perfectly parallel to the bed of the table so that all surfaces parallel to this can be planed accurately.
A large number of holes have to be drilled in the flanges for the cylinder and steam chest covers, and for uniting the cylinders to the frames. Fig. 22 illustrates a modern machine by Messrs. William Asquith, Halifax, for doing this work. It is also used for facing the front flanges to which the cylinder and steam chest covers are secured.
All joints are carefully faced, and covers fitted on to be perfectly steam-tight. The cylinders should then be tested, preferably by steam pressure, though hydraulic pressure is sometimes used.