Minimum Gauge Tank Engine
Project Diary (pt 2)
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| Nov 07 |  A
concerted machining month has seen the next phase of the project
make great progress. The workshop is now covered on a thin,
even film of cast iron dust!
The cylinders, valve chests, pistons, piston rods, and covers are now completed and ready to attach to the frames. Considerable efficiencies were achieved by producing the batch of 6 items. Careful design made sure that much of the machining was symmetrical so the same set-up could be used for both RH and LH sides. The steam passages were machined from solid. This was a challenging and slow operation. Milling a 40 x 8mm slot to a depth of 60+mm cannot be rushed and swarf clearance was a real challenge. Luckily, the the CNC program took care of the repetitive operations allowing me to progress turning jobs on the lathe. In all this operation took 2 days.
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| Oct 07 | 
Final design refinements and adjustments to the rolling chassis design for No 2 have been completed. This seems to have been a long-winded process, but I am very pleased with the result. The technical challenges involved in this loco are substantial and have taken considerable effort and tenacity to overcome. The radiating/sliding axle is shown here with its steering and control mechanism. The telescopic rod ensures that the wheels maintain an appropriate angle to the track. The springs are necessary to ensure the loco points along the direction of travel! With 2 radiating/sliding axles some very odd possibilities have to be considered.....
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The brake gear has been completed and is deliberately substantial. As the leading and trailing axles are radiating applying brakes is impractical so only the middle driving axle is braked. A powerful steam brake will augment the conventional screw handbrake. |
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| Sep 07 | Early September saw a significant milestone for
Loco No 2. The rolling chassis was assembled and rolled out
for initial trials.
In March the first trial had mixed success as the chassis was unable to negotiate tight curves due the excursion of the radiating axle.
This lead to a comprehensive re-design
and it was very pleasing to see that the flexible chassis
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| Aug 07 |  Progress
has been steady over the last months as the second and third
locomotives start to take shape. No.1 has been
converted from the 0-6-0 arrangement seen below to 0-4-2 with the
addition or a trailing pony. No.2 is well on the way
to being a rolling chassis, and is going to be a rather special
locomotive. There will be 2 radiating/sliding axles to allow
it to climb hills and go around bends! No.3 is being
manufactured in built alongside the others but is being stored in
'kit form' until space is available.
The photo shows No 1 being craned onto the track while No 2 is on the build stand.
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No 1 is progressing well and the conversion to 0-4-2 turned out to be very successful. The trailing pony is controlled by a 4 point linkage, rather than the traditional ling radius arm. This ensures that the boiler, ashpan and brake gear can all be readily reached without taking the engine to pieces! The motion of the trailing axle was carefully analysed to ensure that it stays correctly aligned to the track. The axle load distribution can be adjusted by changing the height of the the slide bar. The load on the driven axles can be adjusted by the moving the spring bars.
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The frames and all components are now painted and assembled. The side rods are fitted with sealed ball bearing units to ensure long life and minimal maintenance. It was particularly pleasing that the side rods fitted perfectly without shimming or fitting. I attribute this to good design and careful manufacture of all the components. |
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 No.2
required a great deal of additional design
work to meet the client's demanding requirements. In order
to negotiate 20ft radius curves, the frames have been spread to
360mm and ultra-thin horns and axle-boxes have been devised.
The widest component is the spring which is 25mm diameter.
The horns are cast iron and the axleboxes are ready for the sealed
bearing units to be inserted.
Manufacturing in batches has advantages for efficiency and these are being exploited wherever possible. By producing a bedplate with dowel pins it was possible to batch 3 fly-cranks at a time, reducing the production time considerably. Each one requires 6 separate drilling/reaming operations and 2 table height changes. The time saving achieved by working this way is considerable. Sadly, cutting the internal keyways has to be done manually and one at a time! |
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