NEW DARJEELING & HIMALAYAN LOCO IN 7.25/7.5 INCH GAUGE

THIS project is an international collaboration between John Heald, a veteran live steam locomotive builder in New Zealand, and Mike Massee, a live steamer in the United States. John has built the first locomotive and Mike is producing the drawings according to as-built specifications provided by John and direct measurement and interpretation of the Sharp, Stewart & Co works drawing.

John Heald began the prototype locomotive in January of 2010 in Rotorua, New Zealand. An experienced live steam locomotive builder, John worked from the original plans, adapting as he went.  Around May of that year Mike Massee joined the project and offered to interpret John's as built engine into a set of formal plans, also using the original Sharp, Stewart & Co drawings courtesy of the Darjeeling Himalayan Railway Society as well as the Baldwin drawings from the DeGoyler collection at the Southern Methodist University in Texas. 

The prototype engine is a British engine that was originally designed using Imperial units for an imperial gauge, and the design is a direct divisor of that for 4inch scale,  so the drawings will be in English units. Dual dimensions were tried for a time but abandoned as the chances of an error creeping in were significantly increased. John's prototype engine is a mix of English for overall dimensions and metric for small fitted parts, as he is in New Zealand and has metric tooling.  Those using metric are free to adapt the drawings, and to accommodate metric steel stock for side frames, axles, and so on.

The model is based off of B-Class engine no. 777 currently at the railway museum in Delhi, India.  It is modelled in the period just after the DHR was taken over in 1952 by the North East Frontier Railway (part of Indian National Railways).This period was one of the times when engines seemed reasonably well looked after. The engine would have been painted red during that time, as you see on the model. The engine features the intermediate 'fencing' on the coal bin and sand boxes converted to tool boxes. 

The Sharp Stewart drawings are in 1 1/2" scale. To scale up to approximately 4" scale, direct measurements on the drawing were multiplied by 2.65, also taking into account printed full size dimensions for checking.

Not found in the original drawings are many changes to the actual engines that were made throughout the years, and most of those changes are well detailed in Terry Martin's book The Iron Sherpa: Volume 2. This book is a key reference to those wishing to make a model from a specific time period. It gives colours, modifications and quirks of individual locomotives. Four inch scale was chosen rather than 3 3/4" to give an even 1/3 scale from prototype. 

The B-Class engine has wheels inside the frames and separate bell cranks on the outside. This makes it easy to make small changes to the gauge without any changes to the valve gear or cylinder spacing.   The frame is 10" wide to the inside surfaces, and will accommodate both 7.25" and 7.5" gauge.  The only modification needed to change the gauge is a shoulder on the axles. This represents a change of 1/8" on each side and is not noticeable.

The engine is designed to be as accurate as possible to prototype, with some minor and non-visible changes to accommodate the practical operation of a live steam locomotive. For example, The suspension uses a hidden adjustable coil spring above each axle box, with dummy leaf springs that look identical to the original. This provides for more precise and practical suspension tuning in scale. The prototype model gives a smooth ride with no ‘porpoising’. 

Axle bearings are self aligning spherical bearings and, again, are not visible.  The well tank is made differently from the riveted prototype, and the frame is assembled differently but has simulated rivet heads to appear identical to prototype from the outside.  Again, all looks correct from the outside.  Other parts look correct but vary somewhat internally to accommodate scale practices. All of these changes are geared towards making a superb running live steam locomotive that will require a minimum of maintenance and give maximum enjoyment.

The drawings will cover a range or eras, along with a few suggested modifications to make the engine look older or newer (a big example would be the front extensions to the piston rods, first added by Baldwin, and the extended smokebox).

John travelled to the DHR itself in November of 2010 and documented 13 of the B-Class locomotives remaining in India, including the 777 at the museum in Delhi, and all of the engines, both complete and in pieces, at the DHR itself and Tindharia Works. This provided invaluable information about many questions that were not answered in the drawings, as well as revealing many small details not revealed in any of the other research and literature. Photographs of disassembled engines revealed actual assembly technique which was taken for granted in the drawings and thus omitted. No detail drawings from Sharp Stewart survive, apart from the general erection print. It is quite possible in that era (late 1800s) that there were more detail drawings, but the National Railway Museum in York, England, which holds the Sharp Stewart archives, can only find the one.

Vital statistics for the model are:

  1. length: 7 feet

  2. maximum width (over cylinders): 26"

  3. Height from top of rail to top of stack: 3 feet

  4. Weight fully loaded or 'wet': 750kg.

The valve gear is as per original (see Don Ashton's dissertation on the original here) so running in reverse can be just as practical as going forward. 

On the full sized engine the motion link eccentric  pivot hole centre is directly in line between the piston rod centre and rear axle centre, thus giving what is called a perfect square layout for this type of valve gear. However, there is a back set on the motion link to help set the valves.   

During an air test, the engine was found to run perfectly smoothly at 40 PSI, cylinder cocks open and at any cutoff setting.  The coal bin was filled and found to hold 50kgs (110lbs) of coal! Imagine putting two 50lb bags of coal on your locomotive and seeing what that does to help traction, not to mention the saddle and well tanks.

The coal bunkers are made out of 4mm plate, and weigh 121 lbs (55kg). They will hold about 66 lbs (30 kg) of Australian char!   Enough to go all day. These bunkers are the ones with the low siding and 'fencing' that was added later, before they raised the height of the wall itself. The designers believe this is the best looking period for the B-Class coal bunkers. 

The reverse quadrant is higher up on the bunker than full size due to the fact the right hand coal bin can be used and the quadrant would be in the way. The quadrant has been made slightly longer to accommodate more cut offs in forward gear. Notice only full cut off in reverse.  

The headlight was the last item completed. The back of the headlight is made from a metal mixing bowl that happened to be just the right size and shape!

 The Locomotive received it's NZ boiler certificate and has been track tested at Tauranga. Initial results were excellent, showing a stable locomotive which steams incredibly well thanks to its Duplex steel boiler. It steams so well on regular coal that the door had to be kept open for some of the time to prevent the safety from lifting. Firing it will take some getting used to. This is a very powerful locomotive able to pull many people or freight.

The only issue found on the first run was a tight side clearance on one of the crossheads, which has been corrected.

John’s locomotive received the prestigious Canterbury Award, the highest honour among model engineers in New Zealand.  The award was presented during the main dinner and ceremonies at the bi-annual MEANZ international convention held this year in Whangarei, NZ. The award, judged by an international panel of respected figures in the model engineering community and presented by the Canterbury Society of Model and Experimental Engineers (CSMEE) is for best model of any kind, and not limited to locomotives. CSMEE member Jock Miller presented John with the award, and John thanked everyone who had given him assistance with the locomotive and the prototype 2205 Duplex Steel Boiler. The award is a validation of the great effort that was made to make the engine not only look good, but steam and ride well as it did during the convention and other outings during its inaugural New Zealand summer steam season. 


For drawings and castings see: http://sonadaworks.com/

 

Next time we look at this interesting new type of boiler made from this new (for model engineers) type of steel.