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Stretching a streak

10 August 2010

The idea of stretching an A4 to make a model of the unique rebuilt W1 had been put to me a year or two before I actually started this project, that idea coming from my friend John White for whom I had crafted A2 Irish Elegance by shortening a Bachmann A1 (see September 2007 BRM).

I have to admit that I had not initially taken the suggestion very seriously. I had never much admired what I saw as the strange proportions of the streamlined W1, and I must be a heretic amongst LNER devotees as I’m not that much of a fan of the shape of the A4s either!

On top of that I had assumed, without even comparing photographs and drawings, that the similarities of the two types of loco would only be general, and that all the details would be different, making an accurate portrayal by conversion an enormous task. There the matter rested, until early last summer when I would normally have packed the modelling tools away to get on with exploiting the fine weather.

Other things in life last year were, however, not working out at all as I wanted, and I fancied another easy but interesting modelling job to occupy my time and distract my mind. As it happened, I spotted on an internet forum an N gauge project to convert an A4 to a W1, and for some reason I found that attractive enough to finally make me consult photographs, drawings and the helpful text in the relevant volumes of the RCTS Locomotives of the LNER book series.

Whilst I quickly decided that the N gauge project included a fundamental error in the way in which the A4 body had been extended, I did nonetheless conclude that a OO gauge conversion might be something that I would find ‘relatively easy’ and rewarding by virtue of it being novel.

I soon decided that I’d actually like an LNER-liveried W1 to add to my own fleet, and suspected that once I had successfully built one of my own, others might want me to do something similar for them. That has in fact turned out to be the case – I’ve done three more conversions following my own loco.

Differences

My conclusions on comparing the A4 and the W1 were that from a modeller’s point of view the following were important -

1. The aerofoil curve of the streamlined casing over the coupled wheels is actually the same shape and length on both kinds of loco.

2. The W1 firebox is longer by about 5mm in 4mm scale, and positions of some of its visible fittings differ from the A4.

3. The cab of the W1 is therefore further back, and is in scale 8mm longer than that of the A4, with its side windows in different positions and some ‘not quite-A4’ roof details. Total replacement with the ready-made South Eastern Finecast W1 cab parts seemed a real option.

4. Down below, the trailing Cartazzi axle of the A4 has to be removed, along with the outside frames, to be replaced on the W1 by two axles in different positions and longer outside frames in a different style.

Whilst not prototypical, the most easily modelled arrangement for the trailing axles was obviously a hidden bogie, which again Finecast can supply. I considered making my own new outside frames by restyling the Hornby items or by adding nice Cartazzi boxes such as those by Branchlines, and steps, from some brass sheet.

Using this approach I could have made them with the ‘exact’ appearance, but the cost and work involved was unattractive compared to use of (yet again) the ready-made Finecast W1 parts. Although these lacked some details and had a couple of faults, they were inexpensive and could be easily detailed up and corrected’ in all but one minor respect.

There are two further discrepancies at the front end, as the W1 leading bogie should have a wheelbase 1mm longer than that of the A4 and the cylinder wrappers of the W1 should have a slight bulge. I felt that both of these points were too subtle to bother with, given that the representation of details on the existing Hornby parts was so nice and would be difficult to emulate in a modified or replaced part.

For my choice of a pre-1948 representation of the W1 a corridor tender was required, whereas for post-1948 a streamlined non-corridor tender is correct. As I wished to keep repainting and lining to an absolute minimum, the consequent requirement for a garter blue A4 donor loco with wheel valances and corridor tender meant that at the time my only option was to use the Hornby ‘Railroad’ Falcon.

This was good from the point of view of low cost, especially given the ever present risk of a failed conversion, but it did mean that some details would have to be added if I wanted them, and as it turned out the loco came with the chunky old-style (play-proof?) valve gear and the distorted representation of the corridor tender that was made to house the old Ringfield drive unit.

In consequence, I spent quite a bit of time altering the tender too. I haven’t included the details of those tender alterations here because of the space that it would take up, but if desired I can direct interested modellers to a description of the work posted up on the internet. The following pictures and notes (‘at last’, you say) simply show how I converted my loco, and a couple of others in post-1948 guise that have done since.

The chassis

In any case, the thick top edge prevents the frames from being formed to the prototypical ‘dog-leg’ profile as seen from above, so I decided to remove it and bend the frames to the better shape. That main turn-in should actually be positioned further back, with the leading spring-hanger bracketed out from the oblique part of the frame, but there’s no viable way that I can see to alter that particular feature. The Finecast bogie parts could be used just as received.

I completed the rear chassis end with bogie spring, rear stretcher, some added external details made from wire, washers and scrap etch, a representation of an access hole drilled in each side, plus an all important new body mounting lug ready to slot into the backhead of the extended body. I subsequently also used brass strip to add the two extra loops that pass over each leaf spring, and glued some spare pieces of etched wagon brake gear to the loco body to represent the drop-grate lever below the right side of the firebox, not provided on the ‘Railroad’ model.

The body

The first task was to remove the boiler handrails and ejector steam pipe, as carefully as possible. With the rear end of the body bonded back in place (paying careful attention to alignment), the joint was then built up with layers of thin ‘Plastikard’ until just proud of the adjoining surfaces. I later used a straight-edged very sharp scraper (a freshly sharpened half inch wood chisel, believe it or not), followed by wet 600 grade grit paper on a tiny flat sanding block, to take the surface of the infill material down absolutely flush with the rest of the firebox.

Further details

All body joints and the marked areas left from nameplate removal were subject to much careful scraping and fine wet sanding, filling/priming, further rubbing down and so on until absolutely smooth. Some complicated masking was used to keep primer off the remainder of the loco so that I could save as much as possible of the very nicely applied original livery. By keeping the edges of some pieces of the masking raised, I got a soft-edge to the sprayed areas rather than a step in the paint layer. Original handrail wire and knobs were re-instated as far as possible, although a new length of nickel silver wire for each side of the boiler was needed along with replacement of one or two knobs that broke during initial strip-down. I also used metal strip for lamp irons at the front of the loco, as my Railroad donor loco had none to start with and those on the subsequently converted Hornby finescale A4s appear to be plastic and easily break off during the conversion process.

Painting

I was determined to save Hornby’s nice finish as far as possible, including the difficult-to-replicate parabolic lining on the smokebox sides. Isolated repairs to the main livery colour therefore involved more careful masking, with raised edges again in some areas, and ‘blowing-in’ or ‘fading-out’ the edges of the airbrushed areas with the greatest possible care. Once satin varnished, Hornby’s Garter Blue appeared to be closely matched by the Railmatch shade plus a small addition of mid to dark green.

For Hornby’s BR Brunswick Green I found Humbrol matt dark green (195) to be a good starting point. Depending on the Hornby A4 model batch and the Humbrol paint batch it would appear that a small addition of anything from black, through dark blue to earth brown may be required to adjust the green hue. An overall heavy weathering, prototypical for 60700 may be the easiest way to avoid a visible discrepancy! Repairing the black areas is, thank goodness, easy.
Final touches

For 10000 I painted up the details on the supplied plain black backhead, added cab crew seats, applied ‘teak’ paint around the frame of each leading cab side window and stuck a rectangle of glazing material behind, then applied brass coloured paint around each spectacle and fitted glazing material cut to shape. Thank goodness that the finescale locos I’ve also converted come with all of this ready-done, and the Hornby glazing can be made to fit the Finecast cabsides if the window openings are filed out to full size. Their fall plates can also be saved and refitted, as can the cab doors, and in both cases I’ve used a simple wire hinge to make them at least semi-flexible and less likely to be broken off.

It was even possible to re-use the sight-screen glasses, although removing them from the Hornby cab sides un-broken is a real challenge. Once off and filed smooth on their inner edges, I epoxy glued these into the slight groove between the beadings of the cab side windows. New BR lining on the cab sides came from the Modelmaster range, although I felt that in order to match it to the reddish orange in the Hornby lining it was necessary to rule over it with a bow pen loaded with a translucent mixture of varnish and dark red paint. Numerals are from the HMRS range, including those frustratingly small and difficult to apply RA numbers!

Above are some of the key elements of my first A4 to W1 conversion. Hornby ‘Railroad’ A4 Falcon, the bits from SE Finecast, Railmatch Garter Blue paint (that I hoped to match to the Hornby shade), my annotated copy of a basic A4 drawing stretched to portray the W1, and photos of the original ‘Hush-Hush’ revealing useful details of the rear frame shape.

I embarked on a second conversion (I’m now on my third!), converting a current Hornby Sparrow Hawk into a BR version of the W1, as she was at the end of her life, shedded at Doncaster, valances removed and running with a streamlined non-corridor tender. It never carried a name, though Pegasus and British Enterprise were suggested. TW says it was known just as the un-named ‘Streak’.

Once the moulded plastic Cartazzi frames, and the live rear coupling of the Hornby A4 had both been unscrewed and jiggled free of engagement, the part of the chassis block that carried the trailing axle could be removed using a junior hacksaw and a piercing saw.

The right height for the horizontal cut was just below the line of the rebate in the casting. This cut area needs to be filed as nearly perfectly level as possible. A simple folded brass stretcher to carry the new rear frames could then be screwed to a convenient existing hole in the chassis block.

Off the chassis, the trimmed new frames were soldered on to this stretcher, top edges level. The assembled bogie was suspended from a strip of brass, screwed to the old mounting point for the Hornby frame unit. The extra length of the strip provided for later re-mounting of the live tender coupling. An extra stretcher also went in later to brace the rear end of the frames. Note that my frames turn outwards again behind the Cartazzi axleboxes. This extra widening is described in the RCTS book, is visible in many photos, and provides very useful extra sideplay for the rear wheelset in the model.

Trial running of  the chassis showed the need to either insulate the inside faces of the rear frames to prevent short circuits due to wheel contact, or to fit side stops on the bogie. I opted for the latter, made from projecting stubs of wire, reasoning that avoidance of contact would help to preserve the paintwork on the wheels. Spring loading of the rear bogie (via some springy nickel silver wire) also proved to be useful, both in resisting any attempts by the outside frames to nudge it off the track on curves, and in preventing loco ‘waggle’ at speed on straight track.

Here’s a finished set of rear frames, complete with bogie spring, rear stretcher, some added external details made from wire, washers and scrap etch, a representation of an access hole drilled in each side, plus an all important new body mounting lug ready to slot into the backhead of the extended body. I subsequently also used brass strip to add the two extra loops that pass over each leaf spring, and glued some spare pieces of etched wagon brake gear to the loco body to represent the drop-grate lever below the right side of the firebox.

Using thin razor saw blades, I cut down through the firebox then backwards under the firebox and cab sides. Further cuts were made across the tops of the cab sides, down through those just ahead of the windows, and finally a cut through the cab floor flush with each cab side.

On the first loco I also cut off the rear edge of the cab roof to eliminate the rounded corners, ready to add material to lengthen the roof, having decided against the Finecast replacement roof. In hindsight this isn’t the best approach as it creates the need to remove and then reinstate panel lines, boltheads and ventilator details. As you can probably also see from the pictures, the Finecast cab sides need trimming along their top, front and bottom edges to make them fit with windows in the correct W1 positions.

Ready to create the 5mm firebox extension, I cleaned off the raised firebox cladding band while access was good, then added some ‘Plastikard’ backing pieces inside the body, to support and align the joint. I found that the flat pieces on the sides of the firebox need to be thick slabs (say 0.060”) in order to neutralize a tendency for the re-joined body to become waisted-in at this point. The curved piece for the top of the firebox was formed very easily by trapping the plastic sheet tightly between two round metal tubes of almost the same sizes (an inner and an outer), immersing in boiling water for a few seconds, and then quenching under the cold tap.

The cab roof was extended by fixing a backing layer to the underside of the existing roof and projecting it rearwards. New ventilators were made fom appropriate-sized ‘Plastikard’. Extra studs were made from tiny beads of PVA.Each cabside, once trimmed to size, had a strip of brass soldered to its inner face to create a lip and a rebate along its bottom edge. The brass lip located the cabsides against the inner faces of the moulded rear edge. Expoxy adhesive on the upper, front and part of the lower edge of each cabside then secured everything in place. More plastic sheet was then used to complete the floor of the longer cab.

The longer W1 firebox required a new cladding band in a different position, so once the extension piece was convincingly flush and smooth, I added a strip of 0.005” ‘Plastikard’ about 0.75mm wide to emulate the other Hornby boiler bands. For convenience and to avoid damage when removing/re-instating the body, I transferred the top end of the lubricator drive to the chassis, simply inserting some stiff wire in a hole drilled in the chassis block and retaining the linkage to this with a couple of washers,  glued or soldered in place.

A comparison of two of my conversions (as mentioned, there’s a third on the way). For accuracy (on both models), the layout of some of the round washout plugs and the oval mudhole doors need to be changed from the A4 arrangement, so I cleaned off the offending three items per side, making new ones (using filed-down crankpin washers and a wire stub, then filing the lot to shape - tricky!) to try and match the Hornby originals. For the nearer loco, I found some spare DMR etchings for the the oval fittings. To avoid making more three-piece washout plugs, I took an impression of Hornby’s using silicone sealant, using this as a mould to cast my own in car body polyester resin.  Rather than make an entirely new ejector pipe, I made an extension from plastic rod, centre-drilled to fit on to the original.

Tony Wright reckons I’m mad to take on some of my conversions, especially as there’s a perfectly good 4mm kit available from SE Finecast for the W1. Tony’s model of this is placed in front of my Sparrow Hawk conversion, and it’s interesting to spot the subtle differences. In some ways Hornby’s overall shape is more correct, but I concede that Ian Rathbone’s painting is beautifully done.

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