SEmG

Modelling Notes:
Converting a Bachmann N Class into a N1 Class
 
by Graham R 'Muz' Muspratt

N1

For information on the prototype please visit our N1 Class section.

The Maunsell N1 class, comprising of six engines, was a 3 cylinder version of the N class with the most notable differences being the straight running plate in front of the cylinders, the extended vertical face above the front buffer beam and shallower smoke deflectors. The less obvious difference are the front cab windows where the N1 class has a single curved window on each side of the boiler whereas the N class has a smaller main curved window and a second small circular window above the firebox on each side. Also what I think are lubrication oil reservoirs are located on each side of the running plate just behind the smoke deflectors.
Present photographs are of the model before final painting - once painted new ones will be posted to the page.

Note that the N1 class were fitted with the 3500/4000 gallon straight sided tender and not the sloping sided 4000 gallon tender as per the later (3)14xx N Class.

Differences on the chassis between N1 Class and N Class:
The motion components and the cylinders on the N class are not quite correct for the N1 class.

  • The N1 class outside cylinders are slightly smaller and have much smaller valve chests and so the sides slope inwards towards the top unlike the vertical sides on the N class.
  • The bracket to support the pivot of the radius bar, valve stem and combination lever is supported off the frames on the N1 class and not the cylinder block as per the N class

Chassis modifications:
Cylinder Block -
I removed the cylinder and, carefully with a fine razor saw, cut off the front and back mouldings of the valve chest flush with the main body of the cylinder block. These were saved and added back to the cylinders later. The cylinder block, judging by eye from photographs, was then filed to approximately the correct shape. As the block is hollow you are then left with a hole where the valve chest should be. I then filled this with Milliput® and when hard filed to the finished shape.

The front mouldings for the valve chest were then re-affixed. The rear valve chest mouldings were re-affixed once the brackets to support the pivot of the radius bar and combination lever were removed.

Before re-assembling the valve gear I simply re-drilled the piston rod hole in each cylinder to ensure that no MilliputŪ impeded the movement of the rod.

Combination Lever Support bracket -
New support brackets were made from 1/32" x 1/16" brass flat suitably bent and soldered then glued with epoxy resin to the front edge of the plastic cylinder block bracket. The outside edge of this bracket should be just slightly proud of the edge of the running plate on each side. You must ensure that the brass brackets, one for each side, are insulated from the chassis by a generous coating of epoxy resin otherwise a short circuit will result.

The vertical part of the bracket was made with a 'U' shape piece of 10 thou brass, soldered to the rest of the bracket. The rear of this was drilled to accept the pivot pin on the back of the combination lever.

Valve Rod -
Once the support brackets were fixed to the cylinder block assembly I fitted a representation of the valve rod using a short length of 0.7mm brass rod glued into a hole drilled in centre of the steam chest rear moulding and cut to length to end just behind the new radius arm / combination lever bracket.

N1 Cylinder Block N1 Motion N1 Motion

Body modifications:
One of the reasons that I contemplated this conversion was the fact that I had some spare N1 etchings, which were surplus to requirements from a DJH N class kit I built a while back. These etchings included buffer beam / running plate front and smoke deflectors

Once the chassis was removed I carefully removed the two smoke deflectors. They are fixed via three small lugs and should be pushed upwards from underneath the running plate. As I was modelling the locomotive in 1946 condition I also removed and discarded the AWS box and cylinder mounted on the running plate just in front of the cab.

I removed the boiler and cab assembly by removing the one screw located underneath the middle of the boiler and the one underneath the cab (with the chassis removed the screw at the smoke box end has already been removed). The cab itself was then removed by sliding it upwards from the boiler

Front running plate and buffer beam -
I removed the sprung buffers and shanks and filed flat the buffer beam reducing its overall thickness by approx. 15 thou. which is the thickness of the DJH overlays that I am using. I then cut away the curved section on each side of the running plate, leaving the middle flat section in place.

The DJH (or your own from brass sheet) running plate vertical front and buffer beam overlay was soldered together and a backing piece of 30 thou. brass filed to shape to match the top edge of the overlay and the top edge of the buffer beam on the running plate. This was then glued to the Bachmann running / buffer beam assembly.

The centre drop down section of the running plate in front of the smoke box was raised to match the profile of new front buffer beam assembly using two rectangles of 30 thou. brass, shaped to fit, as the width narrows after the point where the original running remains and soldered back to back and glued into place. The underside of the smoke box was filed flat slightly to allow the filler plate to fit underneath.

I then made the replacement running plate for the gap left following the removal of the curved section using 20 thou. brass; this overlaps the central dropdown section slightly. This was made to be as close a fit as possible and then soldered to the running plate and the new buffer beam to give an invisible joint (in fact the joint with the running plate is virtually hidden on the top by the smoke deflectors).

The outer edge was filed at 45 degrees to thin the edge representing the lip on the edge of the running plate. A piece of 30 thou. brass was soldered underneath to give the full thickness of the running plate. Finally the side edge of the running plate was soldered into place using 20 thou. x 30 thou. brass flat and filed to size to match the Bachmann running plate

Brass sprung buffers (Alan Gibson) cast white metal steam heat and vacuum pipes, lamp irons (cut down Bambi® staples) and small grab handles (0.5mm brass wire) were fitted to the buffer beam.

Front steps -
The characteristic tall front steps of the N1 class were made up from the spare brass DJH N1 step etchings that I had in stock. However these could easily be made from brass sheet or plasticard.

Smoke deflectors -
Again I had spare etched N1 smoke deflectors courtesy of DJH but in fact the Bachmann N class deflectors could simply be cut down to the correct size, although the N Class deflectors have a circular grab hole on the front edge where as the N1 has a rectangular grab hole. This could be rectified with careful filling. Grab handles, from 0.5mm brass rod were soldered in place at the front of the deflector.

N1 Front N1 Front N1 Front

Cab -
I removed the cab glazing then carefully filed flush the front moulded window surround of all the cab windows. The two circular holes were then filled with Milliput® and the front face cleaned off level with the cab front.

Thanks, yet again, to DJH I had a couple of spare etched brass N1 window surrounds which I glued into the correct position and then filed the window apertures to suit (A new window surround could be made either with a bead of fine plastic from heated and drawn-out plastic sprue or fine brass wire and then the front edge lightly filed flat).

New glazing from 10 thou clear plasticard was cut and filed to shape to fit the window aperture to give a flush effect. This was glued into position using a small amount of PVA round the glazing edge, as this dries clear,

N1 
Cylinder Block

Lubricating Oil reservoirs -
Located on each running plate just behind the smoke deflector on each side of the running is what I assume to be a small lubricating oil reservoir / tank. I made these from rectangular plastic rod and glued on the top a small 16 BA cheesehead screw (with the slot filled with solder) to represent the filler cap. /p>

Tender:
The 3500/4000 gallon flat sided tender supplied by Bachmann is correct for the N1. Take care not confuse this with the 4000 gallon tender fitted to the (3)14xx series of N Class which has the inward sloping tops to the sides, as this is also modelled by Bachmann

Removal of Bachmann printing:
I used a BR lined black version of the N Class for this conversion. As I model SR between 1946 and 1948/9 I needed to remove the cabside number, lining and the tender motif, lining prior to repainting the entire model (or course if you are modelling the BR period then you can leave the tender as it is). The printing used by Bachmann can be simply removed using a little enamel thinners on a cotton bud. I leave the thinners on the decal for a short while to soak in before light rubbing off with another cotton bud.

 
N1
The finished model, painted in post war Southern Railway black livery and nicely weathered.
N1

all photographs are copyright Graham R 'Muz' Muspratt.

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This page was last updated 8 February 2004

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