HRP Cylinder Block
With the machining of cylinder castings extra care is essential. On studying the drawings and the casting itself, it will be seen that there is a bore, a base curve and the main and safety valve chest faces; all of which will need to be machined in the correct relative position to each other, and to lie nicely within the shape of the casting (i.e.: machined faces will be square to cast ones, and the base curve as cast will blend nicely with the machining, resulting in a flange of fairly even thickness throughout). The pattern maker takes extra care with cylinders, and knowing that machining will normally commence at the bores, will be careful to ensure that the circular flanges to the ends of the cylinder bore are truly in position; these will be used in the initial location of the cylinder for machining. Proceed as follows:-Using the lathe and a large four jaw chuck, set the casting up with the front or gland end of the cylinder outwards, so that this face can be machined true with the bore. (The back face is not so important.) A cylinder is not an easy thing to hold, and it may take half an hour before it is satisfactorily located and locked in position for machining. Aim to chuck the cylinder in such a way that the non-machined faces are square to the chuck, checking at the base, the side and top of the cylinder, where applicable. The all important point is that the outside of the cast cylinder flange must run true; by this it is meant that the average shape of the flange runs true at the front and at the back of the cylinder.
With the FOWLER compound cylinder the same conditions must be satisfied, but commence on the low pressure, or the largest bore. Now face the end of the cylinder, but do not machine the flange right away; next carry on with the bore, preferably with a carbide tipped tool. (This can be made by brazing a small piece of carbide into a filed step in the end of a piece of J" steel rod, which in turn is held in the boring tool holder.) The bore should be roughed out first with high speed steel, or very light cuts should be taken, being careful that the carbide does not meet a sudden ridge during the initial cutting; a sharp blow to the tool then, would break it. The bore will gradually be brought on size by successive cuts, and it should be completed by several passes at the same setting, since this will remove any possible taper. The only point to watch is juddering when a small cut is being carried out; it may be found necessary to run the lathe very slowly at this time. Having obtained a fine turned finish, the bore is best polished out with emery cloth soaked in paraffin. For this, use a piece of round wood with a split in the end and wrap the emery cloth around it, working backwards and forwards in the bores to eliminate machining lines. During this process keep the emery cloth liberally soaked in paraffin.
CYLINDER BORING ON THE MILL:-This can be carried out very satisfactorily. The best method is to locate the cylinder on a flat face, but this is not very practical with the Fowler cylinder. The BURRELL and SIMPLICITY however, have a flat face to the main valve chest which will be ideal for location, but this must be machined flat and in the right relation to the cylinder bore and flanges and the casting in general. Take great care with this operation, since the accuracy of the whole cylinder depends on it. After locating on this machined face, it will be a straightforward operation to machine the cylinder top face square to it. Both of these machined faces can then be used as a location while machining of the bore and base curve is carried out, the cylinder being clamped aga'inst an angle plate while the top face is pulled downwards onto the milling table itself. (Or onto parallels.) A horizontal arbor is used, supported at both ends, while a fly-cutting tool is employed to carry out the machining, using a fine feed. It is best to use a tool holder, with some sort of screw adjustment behind the tool, so that there will be no problem with bringing the bore to final size. The base curve can be machined next in the same manner, but for this it will be necessary to use a fly-cutting tool supported in a large circular disc holder. (See drawing No. 10.)
Before commencing on cylinder base curves in general, let us take a look at the Simplicity cylinder, since the cylinder bore and the base curve are not parallel to each other; in fact they are out of parallel by 1£ degrees. This angle no doubt, was to give more room for the working parts on this rather unusual design of engine.
In the following paragraphs, machining of the base curve utilising a jig plate is well described. For the Simplicity cylinder the only necessary addition to the set-ups described will be a thin piece of plate, clamped between the spigot and the faceplate. This additional plate will need to be machined to the 1£ degrees angle, and could best be produced by a vertical milling machine using the adjustable top slide, or by careful setting up in the four jaw chuck and using a protractor. All other machining operations will be carried out on the spigot, with the angle spacer removed.
The steam feeds of the SIMPLICITY cylinder from the ports are at an angle, this makes for difficult drilling. However, these feed holes can be drilled straight down parallel with the bore, and the ports themselves connected by a slot drill, in the same manner as described in length for the Burrell engine. At the cover end, a small milled recess will pick up with these feed holes and connect with the cylinder bore itself.
If the base curve is to be finished on a lathe, it can be carried out in one of two ways. The first applies only to a large lathe, where the cylinder can be located on the faceplate on a spigot. (See drawing 20); this will have a step in order to hold the cylinder so that the base flange will clear the faceplate, and at the outer end, it will carry a stud and locking plate to clamp the cylinder in place. During the machining of the base curve, the cylinder will be prevented from turning by a steel clamping bar locked to the faceplate against the side of the cylinder; this taking the thrust. A suitable casting or block of metal of equivalent weight to that of the cylinder should be mounted on the faceplate, in order to achieve balance during machining; this diametrically opposite to the cylinder. A stiff boring tool will then be used for machining the base curve to size.
Single bore cylinders. The spigot is best located on the lathe faceplate by a simple jig-plate (as the drawing 20). This method can be used to locate cylinders while machining the base curve, and is quick and accurate. You will see that it incorporates a bore for the spigot and one for the plug of the lathe spindle; it has two square faces in order to check the position of the top and side cylinder faces relative to the base; also there is an accurately positioned, machined hole which is used to locate a shouldered bolt for positioning the way-shaft bracket, during machining.
A jig plate of this nature is not at all difficult to make, nor is it a lengthy process. Mark it out from your drawing, using very thin sheet metal, thus guaranteeing the accuracy of the job. After mounting up the cylinder on the spigot, it will only be necessary to carry on machining the base curve, until a point is reached when there is an equivalent dimension to the boiler diameter between the boring tool and the machined cylinder base curve. At this point there will be the correct curvature of the base and at the right relative position to the cylinder bore.
FOWLER COMPOUND CYLINDERS. A slightly more complicated jig-plate is used with the Fowler cylinder. This plate incorporates a bore for the nose plug of the lathe, plus a second bore, which takes a spigot bolted to the lathe face-plate. (See drawing 21.) The spigot, in this case, is used to locate the low pressure cylinder bore (already machined), while the smaller high pressure cylinder bore is faced and bored; thus the jig plate gives accurate centre distances between the two bores. A third bore is present in the jig plate, which is used to locate the spigot; once again the low pressure bore slides over this, while the base curve is being machined. The edge of the jig plate is used for squaring up of the cylinder. Providing the jig plate is accurate, all that will be needed is to bore the base curve until a point is reached when the distance between the machined base curve and the boring tool is exactly equivalent to the boiler diameter. Check carefully with the cast base curve. The Fowler cylinder has a base of relatively thin section; it must be borne in mind that when castings of this nature are made they are bound to -distort a certain amount on cooling. This is inevitable, and therefore, when setting up the cylinder, any small discrepancy must be averaged out to blend as best possible with the finished cut.
The cylinder can be machined on a small lathe, but it will be rattier heavy going. However, if the builder is determined at least one flat face will be needed on which to clamp the work (this is already described above). The procedure will be to remove the top slide and to clamp the cylinder down on the saddle, being careful to pack it up to the correct height, before boring with a fly-cutting tool working between centres. The base curve could be machined in the «ame manner, but using a boring bar with a large diameter disc tool holder, working between the three jaw chuck and the tailstock centre.
The next stage with the BURRELL and SIMPLICITY cylinders, using the milling machine, is to mount the cylinder on the spigot on an angle plate and carry out the machining of the safety valve, regulator and governor cavities, and finally the main steam valve recess and ports.
On the single cylinder engines, the face on which the main steam valve slides will need to be end-milled into the casting, so that the steam valve works between two parallel steps. On the original engines, it was generally arranged so that the working parts travelled over the edge of the mating face of the component on which they bore, the idea being that no ridge or step would be produced as the faces became worn. An example of this is the face onto which the main steam ports are milled. We generally find that the ends of the port face are recessed away. Therefore after machining the main port-face to the drawings, mill these recesses. After this chalk the port face, prior to machining the port slots; it will then be possible to lightly mark lines to determine the length of the port slots, also a line can show the commencement of the first port. It will now be possible to bring the side of a slot drill against this mark. When carrying out the milling of the ports, it is best to use the calibrated dial of the milling machine to divide the ports. So, when carrying out the milling of the first steam feed port, make sure the slack of the lead screw has been taken up in the correct direction; lock the slide, and machine the first port. It is essential, when using relatively small slot drills, to run them at correct speeds to keep them true during the cut, and also to take light cuts throughout the machining of the ports.
The following tips should help achieve success:-
(1) Run the slot drill at as near the correct speed as possible (too fast will overheat the cutter, but too slow will allow it to dance off sideways, and widen the slot). See chart.
(2) Cut in one direction only, since this will keep the slot on size better.
(3) When raising the table or lowering the spindle to enable the slot drill to cut, it is best to move the casting past the cutter at the same time. In this way, as the work rises to the cutter, the cut will be progressive over the total length of the port, and thus the slot drill is less likely to kick sideways. Even with this procedure the initial cuts on the valve face should be in the order of a few thous, achieved over the whole length of the port. For less fussy milling, it is usual practice to enter the slot drill fully into the work before each successive cut, but this will produce much more side kick on a small slot drill than the sensitive method described.
During milling of the ports, the milling table will be wound backwards and forwards many times for each port; a great time saver is to chalk-mark the feed dial in order to indicate for both ends of the port. Chalk-mark a line, and put a small arrow head by it; this indicates the direction of the dial when a particular chalk-mark applies, thus there is no confusion. Then unlock the slide controlling the port spacing, and advance it an amount equivalent to the centres of the steam and exhaust ports, and once again lock it. Now change the slot drill and carry out machining in the same manner to produce the exhaust port. It will be necessary to rub off the chalk marks and use fresh ones for this different size cutter. After this move on again, and finish the second steam port with the original cutter. The depth of these ports need be no more than |", and at this stage the cylinder can be removed, and the feed holes drilled from the ends of the cylinder, so that they will end up directly beneath the ports.
The exhaust passage drilling should also be carried out now, being careful to position this so that the outer wall of the drilled hole will blend, or nearly blend, with the bottom of the exhaust port slot. Care should be taken with positioning this hole; a method of checking is shown on drawing No. 22.
Having carried out the drilling, the cylinder may be put back onto the spigot on the milling machine and a slot drill, slightly smaller than the ports' diameter, should be used to drill down centrally from the milled port slots, this should break into the holes of the steam feeds commencing at the ends of the ports; lift the table (or bring the spindle down) until the slot drill has broken into the drilled holes. Then withdraw the cutter, move on slightly more than the diameter of the slot drill in use, and repeat the procedure until a connection has been made across the total width of the drilled holes in the port itself.
In the BURRELL cylinder, no slot drilling will be necessary at the centre of the steam ports. Always use a smaller slot drill, so that there is no danger of widening and spoiling the port slots during this operation. The connection to the exhaust drilling can be cleaned up with the slot drill to be just short of the width of the exhaust port itself, rather than to cut it.
The Single bore cylinders of the Wallis & Steevens 'Simplicity' and the Burrell both have a small milled recess half way up the curved side of the casting; this is to make the drilling of the main steam feed to the safety valve cavity a practical matter. The recess should be milled just slightly deeper than the diameter of the drill to be used. All the main feed drillings on the SIMPLICITY are square to the bore, so these can be carried out on an angle plate, by turning the cylinder at the necessary angle on a spigot. However, before drilling, do carry out a very thorough check to make sure that the holes will come in the correct position relative to the outer wall of the cylinder and the bore itself. An easy method of checking is by putting the work up on a drill press and positioning the drill at the point at which you expect to commence drilling. Next, take a square, and with this resting down on the base and as close up to the side of the cylinder as possible, take a measurement with a slide gauge from the inner edge of the drill to that of the square; now by using the depth gauge of the slide gauge and resting this against the side of the casting, it will be possible to see how much wall thickness will be left between the drilled hole in any particular position (this wall thickness will be equivalent to the amount the slide gauge protrudes beyond the inner edge of the square at any point). Having carried out the final checking, drill the holes; these should now be central in the thickness of the casting.
Two of the feed holes in the BURRELL cylinder i.e.: from the cavity to the safety valve chest, are more difficult, in that they are drilled at a compound, or a double angle. To drill these it will be necessary to have the use of a compound angle plate, or else a small and a large angle plate. The procedure is to mount the cylinder on a spigot on the smaller angle plate, which in turn is mounted on the larger one; this bolts to the base of your drilling machine. The cylinder can now be turned to the required angle, in two directions. Be sure to check with a square, so that there will be no danger of the drill breaking into the cylinder bore or out of the side wall. It will also be necessary to check that the drilled holes will not break into the face on which the regulator valve slides, but will come either side of it. On the BURRELL it is possible to drill the hole to connect the regulator valve to the base of the governor cylinder from the same side as the milled recess for the feed holes. This will then make the job simpler by making it possible to drill two holes side by side from the governor cavity, down into the main valve chest, instead of them being at an angle, to miss this feed when drilled from the other side. One very important point with the single cylinder engines, is that the drilling of the main valve spindle bore should always be left until the cylinder and the wayshaft bracket are initially mounted up on the boiler. The wayshaft will be machined completely, other than the locations for the guide bars, and with this and the cylinder in place and temporarily located, it will be possible to put a special long drill through the wayshaft bore and to make a location in the cylinder to drill and ream for the valve spindle bore; this in exact alignment. For this job a long drill can be made from a piece of silver steel, machining or filing the end as a flat drill, leaving a central web and grinding this up as a drill, afterwards hardening and tempering. Or you may prefer to make a long centrepunch, and follow this up by drilling in the normal way with the cylinder mounted on a drill press.
BURRELL WAYSHAFT BRACKET. The main shank of this, i.e.: to take the way-bar, should be held in a three jaw chuck and the end very carefully centralised and locked. After this, drill right through, being careful to keep central (see drilling of 'Simplicity' front rolls) and follow up by a ream. Now put a piece of rod through this bore and rest each side of the rod on parallels on the drill base; carefully prop the bracket up square, and then clamp it and drill and ream for the main valve spindle. By this method, both bores will then be square to each other. The ends of the bosses will now need facing true, and this may be done by turning a spigot in the lathe. This can either be slightly tapered over the length, or, as my own preference, a parallel fit to the bore, with just the last part of the spigot having a slight taper to lock. The four boss ends can now be faced off to the required dimensions. It will be remembered that the jig plate which was used for locating the cylinder during machining of the base also carried a hole used for machining the wayshaft. With the stepped bolt for this purpose, the wayshaft can now be located, using the valve spindle bore. The two arms to support the guide bars can be squared through the centre of the cylinder bore, and the base brought into position. By again using a steel rod through the way-bar boring, it will be possible to lock the assembly down square using parallels and clamps, or whatever is convenient on your machine. Then machine the base of the wayshaft until the equivalent of the boiler diameter is reached between the machined surface and the boring tool. The same basic set-up can be used if the milling machine is employed. The location for the guide bars is always best left until a check can be made on assembly; it will then be possible to accurately check and mark for machining.
The Wallis & Steevens SIMPLICITY TRUNK GUIDE is the equivalent of the wayshaft bracket, but fortunately it is a straightforward item to machine, since it bolts direct onto the end cover of the cylinder itself, and has no location to the boiler at the front end. There is, however, a separate valve shaft boss; and this should be machined, as should the valve shaft boring to the cylinder. Then with the trunk guide bolted to the cylinder, it will be possible to put a locating shaft through the valve shaft boss and into the valve spindle bore of the cylinder for alignment, while the boss is silver soldered onto the trunk guide.
COMPONENTS WHICH WEAR ON A MODEL TRACTION ENGINE
A model traction engine, if properly made, will last for a very long time. However, there are certain parts which are more prone to wear than others. The eccentric straps, especially of the pump and of the forward eccentric, wear considerably over a period, and in fact take quite a load. Therefore, although less easy to machine, cast iron eccentrics are definitely preferable; since they tend to work-harden on the surface and resist wear for a very long period. Do not be tempted to fit roller bearings to replace the plain ones of the engine; after all, they cannot be authentic and something must be lost in appearance, so be guided by the original makers.
The little end pin and bush of the connecting rod are the only other components which appear to wear noticeably. It is a matter of personal choice whether you make your little end exactly as the original, where a split adjustable bush was normally employed. You may prefer to fit a dummy adjusting bolt and use a straightforward circular press fitted bush; since, on a model this is very easily replaceable, and the hardened pin likewise.
The BIG END, if made properly, seems to be everlasting. In fact, after seven seasons of running, my own model 'BILL' required no adjustment whatsoever to the big end and had no play.
The LINK AND DIE BLOCK should be made carefully, and the slot of the link should, wherever possible, be end milled on a rotary table. It is often possible to make an extension plate so as to obtain the correct radius for machining. (On a small rotary table.) Two simple plates swivelling together, with one able to be clamped down on the mill will do this job. Bolt a long handle to the top plate, so as to maintain sensitive control, and arrange two stops to coincide with each end of the slot; in this way, not only is it possible to mill the working slot, but also the outside contours and the die-block to the correct radius, inside and out. After this very carefully draw-file the inside of the slot and polish with emery cloth; do the same with the die-block until it just fits in the slot. A tightish fit is desirable, since by the time any high spots have worn off, the resultant fit will be just right. Link, die-block and pins should all be hardened for long life, and they are best professionally heat treated in temperature controlled ovens. Whether you use silver steel or tool steel for these components, work to the maker's recommended hardening and tempering temperatures. This way there will be no undue distortion, and the fit of the link and die-block is unlikely to be different after hardening. All other components of the model . . . 'working components' . . . seem to have extremely long life, and therefore the only attention they will require for a long time will be from the oil can.
FOWLER COMPOUND CYLINDER (Refer to 'Princess' drawings). The machining of the low pressure bore and the high pressure bore, also the machining of the base curve, has already been discussed. Therefore, proceed by machining the angle on the top face of the casting; to do this it will be necessary to locate the cylinder on a compound angle plate, or with two angle plates bolted together, to achieve the same set-up. The front edge of the cylinder should be chalk-marked, and a line scribed along, so that it is exactly parallel to a line taken through the cylinder bore centres. Next, bolt the cylinder up on one of the angle plates, using two bolts, one through each bore, with a clamping strip of such a width that it will be possible to take a measurement from the inside of the cylinder bore to the top of the machined face, as the milling progresses. Square the bores up, and adjust the angle plates until they lie at the correct angle for machining, and then mill right across the face until it is completely cleaned up. At this stage it will be necessary to check that the cylinder is correctly aligned, so take a measurement at the inside of the high pressure bore, at the top edge of the face just machined, and then check at the low pressure bore. If the cylinder is correctly positioned, there should be a difference in the two measurements of L.P. bore diameter minus HJ*. bore diameter (divided by 2). If this is not the case, then the cylinder clamping bolts can be slightly loosened, and the casting can be tapped into position, when a further cut can be taken and checked again. The final dimensions will be 3 /16" for the L.P. bore and £" for the H.P. bore from inside the bore to the top face, taken at front wall. It should be noted that the separate valve plate fitted to this face has an extension which completes the flange to the L.P. bore. Once this face has been machined flat, it can be chalked or blued, and the steam feed cavities marked out; there is one for transferring the exhaust from the high pressure to the low pressure valve chest, and another for connecting up with the final low pressure exhaust to the atmosphere. The four cavities which are milled across the face pick up with the valve ports in the separate plate at the centre of the cylinder, and connect with simple drilled holes from the cavity down into the ends of the cylinder.
flBE SEPARATE VALVE PLATE makes the machining of the ports very straightforward, and the general design makes the feeding of steam from the ports to the cylinder ends an easy matter, in what would otherwise be a rather complicated cylinder. This separate valve plate can be fitted by soldering, in which case the two components must be brought up to soldering temperature using a flame. The best method is to use FRYOLUX solder paint, obtainable at most tool shops; this is solder powder, mixed with a very effective flux, in a paste form, and is used a lot in industry. Make sure the two feoes are perfectly clean and then apply solder paint with a rag, and rub this well into the surface. Next put the two components together, and play the flame gently over the cylinder ttniil the solder melts, after which it will be possible to float Ac valve plate on the molten solder, moving this around to achieve perfect coverage. Then finally locate the plate in position and weight it down during cooling. Cast iron is extremely easy to solder, but attempts to achieve this on a large casting by the application of a soldering iron will be completely abortive; always warm the complete casting well up to soldering temperature. A further method of fixing the valve plate is with Araldite; this is very effective and cleaner to use than solder. After lightly coating, the two faces should be clamped together so as to squeeze out any surplus adhesive. During this operation, a piece of flat material must be used to bear against the separate valve plate, then leave in a warm place for 24 hours.
There is a simple steam feed, drilled from a milled cavity under the base of the Fowler cylinder, this passes between the cylinder walls and up through the centre, picking up with an angled hole in the cylinder head. This feed is shown 'X' on the drawings. The angle hole 'X' in the cylinder head is best started with a slot drill, so that the hole will not run out of position.
The exhaust drilling, from the exhaust cavity of the low pressure cylinder, can be drilled directly down between the cylinders, centrally along the length of the cylinder; this drilled hole picks up with one from the rear cylinder wall which completes the passage. However, my long experience of cylinders, together with the difficulty I have sometimes encountered with porosity, has convinced me that it is a better policy to drill across to the exhaust port from the rear cylinder wall and down, just inside the rear wall of the cylinder to meet the final drilling to the atmosphere. This method will then avoid any wasted machining, .since porosity, if it occurs, is nearly always located halfway along a cylinder. However, instances of serious porosity are comparatively rare.
The Fowler cylinder centre casting is a straightforward machining job. Commence with the top flanged face, and machine in such a manner in the four jaw chuck so that the flanges will be of approximately equal thickness all round the casting, since the underside is not machined. Once the top face is completed it will serve as a location while the angle is machined on the underside face; at the same setting, the locations can be milled for the high and low pressure steam valves to slide between. The castings may need some slight clearing above the slideways of the valves, but it is only necessary to just clear the walls away in order to be able to remove and replace the valves.
FOWLER 'PRINCESS'. Now clamp the cylinder middle casting against the angled face, carefully machine the bores for the main valve spindles, and face the stuffing boxes. At this stage, leave the bores undersize e.g: 11164" diameter. These valve shaft bores must be exactly in line with those of the wayshaft bracket in the final assembly and therefore, after the wayshaft bracket base curve has been machined, it will be best to carefully centre the valve shaft bosses on this casting and drill them undersize e.g: 17/64" and at the correct angle. When the preliminary assembly takes place, it will be possible to make up a pilot cutting tool to finally bring the bores exactly in line with each other. This final reaming tool could take the form of a carefully made 'D' bit, on which there would be two steps to cut 3/16" and 9/32", there could be a pilot lead of 11/64" to enter the first hole (See drg. 23).
Returning to the cylinder centre casting, the transfer exhaust port from the H.P. cylinder to the L.P. valve chest is achieved through a hole machined at an angle through the centre wall of this casting. Carefully mark this out, remembering that there must be sufficient thickness on either side of the hole to effect a seal with the separate valve plate, and therefore it is much safer to use an end-mill for this operation, with the casting clamped down.
FOWLER 'PRINCESS'. The machining of the cylinder head casting will not present any difficulty, other than in the angle drilling 'Y', which passes across to the governor feed after connecting with the regulator face. The best method for starting this hole is by use of a slot drill; other than this a block can be soldered onto the step of the casting, or can be clamped against it while the initial drilling of the casting is achieved. There is a thin gasket fitted between the cylinder head and middle castings on final assembly. FOWLER 'PRINCESS'-CYLINDER BOLTING TOGETHER
There are five countersunk bolts which go through the middle casting only, and these are screwed tightly down into the cylinder base; however, the holes should be drilled as close in to the inner wall of the middle casting as is possible, in order for them not to foul with the drilled feed holes in the ends of the cylinder (underneath the valve plate). The cylinder head is held on by 27 studs and nuts, there being 5 each side of the cylinder, passing right down from the head to the base, 3 likewise passing through the centre wall into the base, and then a further 14, which are short studs, passing only into the flange of the cylinder middle casting.
PISTONS AND RINGS. The turning of the pistons needs little description other than that the grooves should be on size, and that the bore must be concentric. If using a gun-metal piston in a cast-iron bore, allow sufficient working clearance (.002" would be satisfactory); otherwise with the larger expansion of the gun-metal the piston could well seize up. PISTON RINGS In a steam model I firmly believe that bronze piston rings are ideal. It is true they are not powerful rings, but they do not need to be; they have the added advantage of not being able to rust in the grooves of the piston if the engine is mis-used. Sometimes one sees model pistons fitted with commercially made iron rings; these are often extremely powerful causing a stiff engine and unnecessary wear. The bronze rings can be made by machining a bronze bush in the lathe, turning the inside diameter and the outside diameter so as to give the finished thickness of the ring, and for the O.D. to be 1/16" oversize to the size of the cylinder bore (this is ideal for a cylinder of 2" bore). Next, using a parting tool of a known width, face off the edge of this bush; advance the parting tool along the bush an amount equivalent to the width of the finished ring plus that of the parting tool, and part off carefully. Do this again for as many rings as you require. After this, rub them on a piece of fine emery cloth resting down on a flat surface to remove the burrs, and at this stage, rofl the rings in the grooves of the piston until they just fit nicely. After this it will be necessary to cut the rings through, and then work them backwards and forwards with a fine ;iat file between the ends, until a gap of approximately .004" to ,005" is achieved between the ends of the ring when it is placed in the cylinder. This method of making rings is quite effective; a very slight amount of distortion takes place when the ring is closed, and therefore at the initial stage the ends of the ring may not lie truly against the cylinder wall; this is a small point, since the bronze quickly beds in giving long service and an efficient seal. A more elaborate method is to machine the bush to finished size on the inside, and then to finally gap this bush as a whole, after which clamp it down onto a spigot of the correct diameter, using a large jubilee clip and then carefully skimming the O.D. on size. Parting off can then be carried out in the same way as described above, but it would be unwise to part right through, in view of the split rings; they are best finished off by hand. In theory the latter method is far superior, but in practice, after bedding in has taken place, there is little difference.
WATER PUMP AND CHECK VALVES
There seems at times to be a reluctance on the part of model builders to trust themselves to make water pumps, generally because the pump is regarded as an important component of the engine, working against boiler pressure. As it happens, the machining is mostly straightforward drilling and reaming; the main points to watch are-the seating of the ball valves, and the fit of the ram and gland. The ideal way to produce a good valve seating is to use a flat bottomed drill so that, at the point of contact, the balls will rest on a 90 degree corner. To make the seating, use one ball, rest this down on the seating and give the ball a sharp blow, using a piece of rod and a hammer. This procedure should produce a perfect seating; a narrow ring should be evident on inspection. A narrow seating is much the best, since the contact pressure will be very much higher when working; now throw away the ball which has been used to produce the seats, and use a new pair for the ball valves themselves. The same procedure is carried out when making the valves of the clack or check valves; the only additional points to watch are firstly, that there is sufficient room all round the ball to pass water, and secondly is to be sure that the ball cannot lift straight up and plug the delivery hole, which will be almost directly above it; to prevent this, there is usually a stop rod, if there is excess clearance above the ball. For details of machining the check valve shut off cocks, proceed as at drawing 13 and text.
The Burrell model check valves are flange fitted to the boiler; the face which fits against the boiler can be ground into the necessary curve (by hand) on a standard 6" diameter grinding wheel. After this put a piece of medium emery cloth round the boiler and work the valve over this so as to produce a final mating face. When the two fixing holes have been drilled in the flange a Woodruff type cutter or small milling cutter should be used to machine a curved cut on each side of the back of the fixing flange, this curved cut should be taken far enough into the valve centre, so as to allow the nuts sufficient clearance. (This is exactly as the original Burrell check valves.)
The Fowler and Wallis 'Simplicity' check valves are easier since they have flat flanges; the boiler having flat bosses ready brazed on.
GOVERNOR:-The governor is a very precise piece of model making, and rather time consuming. However, it will be well worth the time involved; models pull very nicely when coupled to the governor, and they look most attractive to the crowds. The governor piston itself should be a nice sliding fit in the cylinder, but do not attempt to make the piston so good a fit that it is liable to stick. Remember that at no time does it need to completely shut off the steam, but only needs to control it, and working clearance is very definitely necessary if a governor is to operate properly, as its return mechanism is not very positive. Sometimes modellers are puzzled by the
The governor and safety valves on the original Burrell T.E. 'Bill'.
working of the governor. Basically there is a main spindle passing down through a gland and this is joined to the governor piston by a simple form of universal joint, allowing the piston to align with the cylinder so as not to stick; yet at the same time allowing steam to pass through it, so that the pressure is equal above and below the piston. There must be no upward thrust imparted to the piston by steam pressure. The top end of the main spindle is connected to the three balls, which operate as the governor revolves. The piston should be so set, that when the balls are fully out, the piston will have just completely covered the feed holes of the governor cylinder. The spring steel strip on which the balls are mounted acts to some extent as a return for the mechanism, as well as supporting the balls. In addition to this there is a coiled spring which is housed in a tube; this spring has a peg at each end of it, one end being located in a small worm gear, and the other end in a return fork. When the small worm gear is turned by hand, the worm wheel will wind up the spring, and this in turn will transmit torsion to the fork and produce an upward thrust on the main spindle of the governor, lifting the piston. In the original governors, the purpose of this screw adjustment was to vary the speed of governing, to some extent, for various jobs. However, whereas a model governor will work extremely well, this mechanism can only really be regarded as a return mechanism, and will have little control over the working speed of the governor. The governor is one of those components which do not scale terribly well, and although they work extremely effectively, they generally seem to work ideally at about 400 R.P.M., whereas the original engines were governed to approximately 250RP.M.
GOVERNOR BELTS. Thin skiver leather makes a good driving belt, this can be cut to twice the width and be folded and glued with contact adhesive, or used singly according to the required thickness. Clips should not be used on small belts, otherwise slip occurs as the clip passes over the small pulleys, with the result that the speed is not constant. To join, simply overlap the belt and sew together along each edge; when the belt stretches, adjustment by the same method is easy to achieve. (Skiver leather can be obtained from handicraft shops; it is used for making wallets, handbags etc.) DYNAMO BELTS. These can be made as above, but it is possible to obtain (from belt manufacturers) small fiat canvas belts as they are used in industry, although they are generally not made small enough for the governor drive.
The balls of the governor can be produced by using 6 balls and machining half of them away, ultimately slotting and screwing back together, or by using 3 balls and sawing a fine slot part way through them; either method is satisfactory.
The former method may well be the most popular, and this is generally carried out by machining a location into the end of a piece of rod, and then soldering a ball into it, while half of the ball is turned away in the lathe.
CROSS HEAD. The fixing of the cross head to the piston rod by wedge, in the traditional manner, takes a lot of beating. It should be understood that the wedge should bear on the front edge of the piston rod, clearing the back edge of the piston rod slot, while the back edge of the wedge should bear on the rear of the slot in the crosshead and clear the front end of this slot. In this way a perfect locking is achieved.
The same principle of locking with a wedge is applied to the BIG-ENDS. A description on making these is unnecessary, since they are very similar in general design to the crankshaft bearing.
MAIN STEAM VALVE. The main steam valve should be carefully machined to the dimensions on the drawing, the working face having a fine machined finish. After this, polish it smooth on a piece of fine emery cloth resting down on a flat surface; the cloth can be damped in paraffin. Now it will be necessary to finally grind the valve into the port face, but this is only carried out when the port face is as smooth as possible. A new end-mill will produce a very smooth finish, after which a small piece of fine flat file (broken off for the purpose) can be worked backwards and forwards over the port face, using a piece of wood to push it with; wood grips nicely in th£ teeth of the file. The piece of file should have flat faces ground on both its sides so that it will not cut the slideways. After producing a good surface with no depressions, use emery cloth underneath the file, this being wrapped around the piece of file lengthwise so as not to touch the side walls. Final grinding of the valve to the port face is carried out, using a very fine abrasive paste such as that used by coach painters for removing the egg-shell finish from sprayed surfaces. Try and keep the paste off the side walls, and work the valve backwards and forwards, constantly lifting to spread the paste, so as to avoid lining. A final finish can then be obtained by the use of metal polish; after this both the port and the valve surface should be thoroughly washed in paraffin to remove any grinding particles.
Machine the VALVE CARRIERS so that they fit nicely on the valves with the light springs fitted into their grooves (these are only to keep the valve against the port face until there is steam pressure). Do not drill and tap the valve carriers for the valve rods; this is best carried out on assembly. Then, with the valve carrier pressed in but not quite home against the back of the valve, it will be possible to spot through the cylinder, marking and then drilling and tapping for the valve rod. The valve rods themselves are generally adjustable in some manner, even if only initially to centralise the valves. When the engine is in full forward or reverse gear, the valve or valves should travel so as to uncover an equal width of port for each end of the cylinder. When set for forward gear if all components have been made correctly, the valve should also be central in reverse gear. Thus in the finished engine it will be possible, when the engine is just ticking over (almost stopping) to move the reversing lever from forward into reverse gear, and the engine should continue at the same speed exactly, in forward as in reverse. If, however, it is impossible to carry out this adjustment correctly, then the fault must lie somewhere in the linkage i.e: from the eccentric and rod through the link to the valve shaft. In this instance it should be possible, on checking, to decide whether lengthening or shortening an eccentric rod will cure the trouble.
EXHAUST TUNING. A traction engine, just like a car, does not necessarily run to perfection the moment it is assembled, but needs trials and observations; all engines vary and each builder's interpretations of the drawings will vary too. However, the only component that may need attention is the exhaust. So observe the manner in which the engine steams, whether too great or too little (the latter in fact is a rarity), and tune the exhaust pipe by opening or closing the bore. A smaller bore will produce exhaust gases at a higher speed, since the same volume must escape; a larger bore will produce gases at a lower speed. In theory the smaller bore will give greater suction on the fire, but hi fact this is not necessarily so, as the steam may not spread sideways; it should strike the side walls of the chimney at a point 2" to 3" above the exhaust nozzle. Generally speaking, a small bore of any length will produce a fine jet of steam; this is unsuitable. Therefore it is often best to insert a thin end plate into the exhaust pipe nozzle and drill through this; it will then be found that the steam will spread sideways rapidly. These remarks are really addressed more for the perfectionist, since a model made exactly as drawn should perform more than satisfactorily.
Speaking about models in general, if it is found that an exhaust on a traction engine does not seem to achieve its object, carry out the preceding suggestions and check the spread produced by the exhaust nozzle by forcing water through this from the tap, using a rubber tube. In railway engines a device, known I believe as a 'Jenny', was sometimes fitted across the exhaust pipe when a driver had a particularly bad steaming engine. This quite unofficial addition was a piece of wire wound round the exhaust nozzle, with a single strand passing centrally across the blast; this had the effect of splitting the exhaust steam and diverting it more sideways, creating greater suction on the fire. When these wires were used, they were generally removed before the engine was returned to the sheds at night.
SAFETY VALVES:-The BURRELL and the SIMPLICITY single cylinder engines have a flat seating, whereas the FOWLER has a seat at 45 degrees. This type of valve is of a very simple design which indeed it needs to be, safety valves must be fool-proof. The general principle of the design, is that of two identical valves kept in position by an arm with a fixed, and a swivelling centre to locate in the recesses of the valves. A single tension spring in the case of the BURRELL and the TRACTOR, and a compression spring in the case of the FOWLER and the SIMPLICITY controls the valves. The shanks of the valves are generally triangular, so that they pass steam by them, and yet at the same time loosely locate the yalve in the safety valve chimneys. If the valves are well ground in, finishing off with a very fine paste, they will be extremely trouble free.
One sometimes sees traction engine models fitted with 'pop' type safety valves and a dummy lever and spring arrangement, but do not commit this crime; it looks wrong, and it is wrong. From a safety point of view, two valves linked together have twice the chance of releasing that single valves have so why alter them. Be sure to make them correctly. Springs supplied for the safety valves of the BURRELL and TRACTOR are pre-loaded to commence movement at a definite pull; this, in conjunction with the valve inner surface area in contact with the steam, determines that the safety valves will release at the correct pressure. When fitting safety valve springs of this nature, it is only necessary to just take up the slack when assembling the valve. The design of this type of safety valve always incorporates some form of link, whether it be inside the springs as in the BURRELL and TRACTOR or achieved above the spring. The idea is to limit the amount the valves can open in order that they cannot blow clear of the safety valve chimneys should the spring break.