Pixie's background and build
I am fairly proud of the model that I built from a survey and from raw materials and castings. I learned a lot about the loco, its builders and the folk who maintain and run it.
In this page I include background on the loco, a description of the parts and comment on the build. The work involved is similar to that in producing other locomotives to any scale and hopefully will help other modellers, as well as interesting those who just enjoy railways and all that.
Copyright of G.A.Cryer
Near Twins, Pixie (Foreground ) and Peter Pan
The writer's decision to model PIXIE the Kerr Stuart ' Wren' Class locomotive KS4260 / 1922 was based upon several factors. First and foremost was the impression I had on sighting the little locomotive as it coasted into Pages Park Station on the Leighton Buzzard Narrow Gauge Railway one spring afternoon. It seemed incredible that a locomotive, produced initially for work on the installation of a sewer in 1922, should 60 years later be found running like a Rolls-Royce and doing useful work in a domestic setting.
Enquiries revealed a little of the history of the locomotive, the fact that after the completion of the Barkingside sewer contract it had for some years worked in the Wilmington Road Quarry of Devon County Council, eventually being purchased by the Industrial Locomotive Society and brought to Leighton Buzzard in the late 1960's. The locomotive has an overall length of something over 10 feet, it weighs 3 Tons 7 cwt empty, and 4 tons 3 cwt in working order. The inside framed locomotive has Hackworth valve gear and is resplendent in attractive livery of black, green and gold.
My thanks go to The Directors, Managers and Staff of the Leighton Buzzard Narrow Guage Railway for the access allowed me to their site and the unstinting provision of know-how and information during my many visits to the railway.
The finished model on narrow Gauge track is a ' Two man lift '. 29" ( 74cm ) in length, 12" ( 31 cm ) and stands 21" ( 53 cm ) High
of the model commenced with the frames, axle boxes and
wheels, here the motion work has been added and the
weighshaft and its bearings installed.
Further illustrations follow:-
Here was a locomotive that was mechanically quite simple for a relative beginner to construct, It would be accessible for survey and was in the hands of friendly folk prepared to assist with provision of information. The railway was within 25 miles of home base, so that the survey could be staged over a series of visits. Above all, the locomotive had an atmosphere and charm which appeared to the writer to convey the very essence of narrow gauge railways. The decision has never been regretted and has, over the past twenty years, opened up a whole new interest in the mechanical engineering of railways and of narrow gauge railways in particular.
At this stage the modeller intending to work in narrow gauge has to come to terms with the fact that just as much work will be involved in producing his chosen model as in producing one to run on standard gauge. Pixie was ten years in the building, through choice. Some things are too good to hurry and although one is always keen to get one's locomotive onto the track, later efforts can be savoured, and perhaps greater attention paid to detail.
With the exception of the boiler, lubricator and gauges everything including patterns for the castings was produced from scratch.. Occasionally where there was only a small difference from the scale dimension it was possible to use off- the-shelf materials for platework, shafts etc., otherwise sawing, milling, turning, filing and polishing were the ' Order of the day '
further additions the locomotive begins to take shape.
On the right is the jig for the blower ' Plumbing ' Jig and template construction is a time consuming but essential part of the assembly process.
At this stage the engines on each side can be tested using compressed air.
At this stage in the build, not having a compressor I took the loco to the local garage. Imagine the mechanics surprise when the 'Mechanism ' shot across the garage on the end of the air line !
Although construction of a sizeable standard gauge model locomotive may make excessive demands on the capacity of one's workshop and equipment, narrow gauge locomotives are generally simpler in design and, at the same scale, work up smaller in model form. ( This fact can be used to advantage by the modeller 'moving-up' to a larger scale). The flavour of work and operations on a narrow gauge line can be replicated within a small workshop and in ones own backyard.
Model engineering activities ' along narrow gauge lines' provide every opportunity for the incorporation into models of the very things that attract us to the prototype, to make and handle the artifacts that would otherwise, unless one works as a volunteer on a preserved line, be literally beyond reach. It should be remembered however that modelled on 5" Gauge quite a small locomotive such as PIXIE, at some 10 feet overall, will be more than 25" long in model form and of such dry weight that it is beyond one (normal) man's lifting ability! Quite apart from the weight of the model the physical size, 25" long x 11.5" wide by 20" high are dimensions to be reckoned with when it comes to handling in the workshop and between shop and track!
The survey and construction process
During a preliminary visit to the Leighton Buzzard Narrow Gauge Railway at Pages Park, Leighton Buzzard ground rules regarding my access to the prototype were outlined by the professionals and amateurs who operate the line. I was permitted to commence my survey. Many hours were spent in the engine shed and along the line sketching, measuring and photographing the locomotive.
From the dimensional drawings made at Pages Park, sketches were made of the key compnents, these would provide an overall picture of the parts to be made and prove useful in esatablishing the sequence of fabrication and machining operations
Materials were ordered, patterns made and construction commenced with...the Chimney ! This being to our mind one of the defining features of the locomotive as are the engine, motion and the saddle tank. Work on such a model is mainly in mild steel, phosphor bronze, cast iron and in my case stainless steel, all requiring differing machining techniques.
Castings were produced by a friendly building fixings firm specializing in bronzes and alloys.
With the valve gear installed and the smokebox and chimney mounted, we awaited the boiler.
There was plenty of work to do however, fabricating the saddle tank, and completing the cab, plumbing, brakes etc.
The sheets alongside Pixie area few of the many ( 150 ) dimensioned sketches prepared at site
Now the locomotive is really taking shape. The major components are assembled, mainly constructed using stainless steel. The saddle tank is of mild steel for flanging purposes, lined with fibreglass.
Cast items, cylinder blocks and valvechest combines, als wheels were cast from phosphor bronze using hardwood patterns prepared from site sketches.
Coupling blocks are fabricated from 12 pieces of mild steel, welded and shaped by grinding.
Among the more difficult items of construction for the ' Tyro ' was the weighshaft and dieblocks which provide the means of reversing and adjusting the valving, being rotated by a lever on the footplate.
The accuracy of the work in dieblock illustrated is critical to the performance of the locomotive.
Due to the considerable heat requirements in boiler manufacture, unlike in the case of Tich which boasts a home built boiler, Pixie's boiler was purchased from Cheddar Models who manufactured to the survey sizes, with due adjustments to ensure free steaming.
With the boiler and all plumbing installed A start could be made on painting. This necessitated complete dismantling, degreasing and removal to a dust free environment ( The greenhouse )
Bondaglass primer was applied followed by many coats of spray applied cellulose and acrylic paint'
The smokebox and chimney received motorcycle exhaust enamel
Of course a driving trolley is an essential in the case of models of this size and a prototype was selected such that coal and water could be carried if required. To reduce drag the wheels, turned from a billet that I found on the road in my travels ( It had literally fallen off of a lorry ! ) were fitted with ball bearings. Snatch on startup is reduced by a heavy spring around the drawbar.
Pixie and driving trolley, note the well upholstered seat !
P.S. The sleeper spacing is typical of certain Narrow Gauge. Railways ! No names no packdrill.
The end result
The completed model was tested on compressed air at the local garage to the amazement of two motor mechanics it shot across their workshop, nearly destroying some of their equipment. The model was steamed several times on a test track in the garden. As is my practice I cleaned all preparatory to priming and painting in generic colours (Unlined) and added it to my collection.
Years on, I still have the pleasure of owning and viewing the model. Memories of the building process which involved a whole new learning process for a concrete engineer are ' Worth their weight in gold ! '
|Pixie completed, gleaming in a generic paint job. It has been steamed and then cleaned-up. Here the loco has the ' Show ' cab installed. The alternative is a ' Driving ' cab which has openings for access when firing and to enable a view of the gauges.*|
*There are two roofs and two rear spectacle plates, one is complete for exhibition, the other is a skeleton to enable access to the controls and for firing. That in the image above is the exhibition set-up.
A look back at the construction
As a response to visitors to the site who have mailed requesting more information on the model this section has been inserted as a supplement to the page on Pixie, The illustrations are described for the enjoyment of the narrow gauge locomotive enthusiast. Construction techniques are described and will hopefully assist in the construction of models of a similar nature.
A look around the loco
This general view of the completed model which is 25" long x 11 1/2" wide x 20" high overall conveys the basically simple design of the locomotive. Set on 5" Gauge track it is stable and powerful. In this image the exhibition ( scale ) roof and spectacle plate are installed in place of the model's driving roof which has apertures for viewing gauges and handling controls)
This view of the locomotive under construction shows the frames with the riveted angle steel stiffeners, Rigidity is ensured by transverse frames and the smokebox saddle, substantial angles also contribute at the joint between buffer and drag beam and main frames.
Overhead view .The leaf springs are ' dummies' although correct in detail. Actual suspension is catered for by rubber blocks inserted between the upper horn member and the axle boxes of the front axle. In practice this proves adequate to provide equalisation. Further detail in the above illustration will be described later
The smokebox saddle is evident in this view it was cast in phosphor bronze at the same time as the cylinder blocks. Not being an expert pattern maker, rudimentary oversize patterns were produced, allowing the required shapes to be 'excavated' by milling, drilling and boring.
The coupling blocks were fabricated from a number of TIG welded pieces of mild steel. This avoided the task of making a pattern with cores to form the slots. These assemblies were subsequently milled and ground to shape.
This illustration shows the loco with some of the major features installed, notably the cylinders, motionwork, smokebox, spectacle plate and bunkers. Although the frames etc. are bright mild steel,the platework is mainly of stainless steel, quite tricky for the amateur to work, drill bitts are easily burned out unless kept cutting, but it is guaranteed to ensure longevity ( Of the model ! )
Here is a last shot of the main components, in the raw. I like to see the model parts in the bare metal stage the Stainless and Mild steel gleam although the Phosphor bronse is beginning to oxydise and will need a clean up prior to painting. Details
The wheels being solid(spokeless ) were cast from a simple pattern of turned hardwood produced by a woodturner friend. The balance weights were carved and planted onto the pattern prior to despatch to the foundry where they were cast in grey iron. The crossheads were fabricated from m.s. and fitted with slippers milled from phosphor bronze
The cylinder and motion plate provide fixings for the slide bar. This image shows the marine type bearing to the coupling rod also the valve rod cylinder and valve chest glands and the lubricator. The drain valves are steam operated. On top of this RH valve chest is a take-off connection for the valve chest pressure gauge
The slide bar is cut from bright m.s. The section is reduced at fixing points by milling. There are 3 recessed, through holes in the slide to allow oil from the oilboxes to get to the lower of four slippers. The glands are from phosphor bronze turned to profile then hand filed to final shape.
The Weighshaft sits in bearings bolted to the frame angle. Phosphor bronze die blocks with the spindle for the vibrating lever slide within the steel slides, The inclination of the slides determines the valve sequence.Brass oil boxes with knurled filler caps replicate those on the prototype
' Full frontal ' view of Pixie shows the sandboxes, actuated by the push rod passing over the saddle tank. The chimney was turned (with difficulty ) from a length of high tensile reinforcing steel from a construction site. The profiled buffer beam permits withdrawal of the pistons, the backend of the cylinder block being solid. Immediately behind the buffer beam is an axle-driven pump for topping up the boiler, this is of course not required on the prototype with its injectors.The chimney was tapered between centres The saddle was produced intially by turning and subsequently by filing.
The twin pipes over the safety valves are a nice feature of Pixie, these sit on bushes on the steam dome and are positioned by a bracket attached to the cab roof.
We like to see the bare metal................it gives us something to polish !
The safety valves. One brass steam pipe has been removed to show the spring and adjuster nut on the front valve spindle.
Under the dome is a bush with scewed plug, used when testing the loco on air.
The filler cap on the fully rivetted and soft soldered saddle tank. The front and back plates of the tank were hot formed over a 1/4" thick mild steel. former.
A departure from scale here, the aperture in the tank top gave access for installation of the g.r.p. lining selected to protect the m.s. tank plating.
The lamp is a faithful copy of one that was purchased at a car boot sale. The lenses are of perspexx which can be simply turned and polished when attached to a wooden block on the faceplate .
The footplate and boiler backhead
Much of the fun in building Pixie came from the detailing, some might call this ' Rivet counting ' Pixie is not a super scale model and where stock materials were close in scale size to those of the prototype, stock materials were used. Details such as the number of rivets in the platework have however been adhered to also bolt and rivet sizes are to scale to the extent that the main angle to frame rivets have been turned from stock.
The regulator valve is sited in the steam dome and actuated by the regulator lever. The cleading to the boiler is trimmed by an angle steel conforming to the outline of the backhead. The shelf copied from the prototype must provide an excellent storage place for the driver's tea can.
The boiler for Pixie was built by Cheddar Models as at the time of constructing the model we had insufficient means of heating such a large mass of copper !
The Firebox door ( here lacking a chain ) can be operated by the crew's shovel. The valve on the left is a bye-pass valve for the non-scale axle driven pump. at the bottom of the image the red bar is the handle to the damper, most important in controlling the air to the firebox I am sure that the visitor can sense the thrill experience when firing up the loco for the first time after some years of anticipation! Paraffin soaked sticks and some crushed steam coal soon generated enough steam to permit the blower to be employed in building the 'incandescence' necessary tp power up the works. We tried a gas burner earlier but it was unsuccessful, Coal is the thing . The bunkers are from stainless steel, bent round a slightly tapered hardwood jig, allowed for the spring properties of the sheet Makers plates were photo enlaged, and the black and white negative sent away for etching onto brass, on receipt they were flooded with enamel and polished back to expose the cast lettering. This image is from the prototype.
Here are the footplates (stainless steel plate) and the brake standard, both with a coating of ash and needing cleaning up. The brake blocks bear on the tread of the rear wheels and even in the model are quite powerful.
There are two gauges on the back of the spectacle plate ( Purchased items, more of a watchmaking job that we could face !) The upper gauge is the boiler pressure, the lower is the steam chest gauge for the right hand cylinder block. We are inclined to think that the steam actuation cylinder for the drain valves was not part of the original locomotive.
This is a drivers eye view of the backhead taken through the drivibg back. With this back replacing the scale back the loco can be fired and the gauges eaily seen. In the LH bunker is a hand pump. Coal is stored in the driving trolley.
The prototype has one water gauge, and two bibcocks for determining the boiler water level at present the model has just the gauge.
This Is the scale back. The polished spectacles were trepanned from brass plate bonded to a wooden disc screwed to the lathe faceplate. The platework is attached by scale numbers of soft iron rivets to m. s. angle steel which will take the gentle bend of the roof without heat. Joints are silver soldered throughout.
On the track at last
An exciting time ! First run on the temporary track, No 2 son at the regulator. The driving trolley replicates a wagon on the Talyllyn N.G. Railway.
Last revised: 23 rd June 2006