Construction of a model Bulleid Light Pacific: West Country Class Locomotive No. 34008 Padstow

6 Sept 2010 Chassis phase 2  
 


'Here's one I made earlier' - the target is to produce something a lot better than this!

There's been a bit of a false start building the chassis. The kit I'm using has 'machined' spacers for holding the frames together. These transpired to be unreliable as a means of aligning the frames. Fortunately the kit includes etched (additional) spacers for the main-frames, which I've employed for constructing the chassis.

This upside-down view shows where I've used the three etched-spacers to construct the chassis. I've also soldered in position the plate for the bogie pivot. At this point, I chose to mount the motor and gearbox - see later.

Overhead view shows that I've yet to clean-up after the soldering of the spacers, slide-bar support brackets and front & rear cylinder faces. When the latter four pieces are soldered in position the chassis front-end is considerably stiffen. Note I've used one of the offending 'machined' chassis spacers to the rear of the trailing driving axle. This will be the for the pony truck's pivot.

This was the first opportunity to test-run the chassis on a length of track - motor leads connected by crocodile clips to the controller. I'm pleased to report that the test was passed with flying colours, no stickiness anywhere, and in the complete absence of oil - I had checked the chassis without the motor, first!

The next job is the construction of the motion. The coupling rods are the most crucial in that they have a major affect on the smooth running of a model. The above photo shows the completed, right-hand, coupling rod (with crankpin components added) in front of the three etched Nickel-Silver laminations, which form the rods. The completed rod has received a partial clean-up following the soldering together of the laminations.

The next two photos show the amount of articulation about the centre crankpin. The coupling rod needs to be articulated to allow the centre axle (in my model) to rise and fall courtesy of the elongated holes in the main-frames, for the axle bearings.



Photos showing the amount articulation possible - somewhat excessive, but better more than less!

 

 

 
9 Sept 2010 Chassis phase 3  
  This is where it gets interesting!

The construction of the coupling and connecting rods is a fairly long job in that there's quite a bit of cleaning, filing and buffing to be done. The good news is that the final buffing with a wire-brush in a mini-drill results in very smooth and shiny rods. Although not made of Steel, Nickel-Silver finished in this way looks quite convincing.

Note I haven't put on the washer and nut on the centre crankpin. I tend to leave these off until I'm satisfied the rods are running true and not binding - any problems and they tend to work off the crankpin as the wheels are rotated.

It can be seen in the above photo that the leading driving wheels are very close to the rear slide-bar support bracket. In fact, I've filed a notch in the bracket to provide adequate clearance.

I've taken a (very) short video in an attempt to show how free-running the chassis is. The angle of view makes it look as if I gave the chassis a good shove - I didn't, honest! However, the merest incline of the track does result in the combined weight of the coupling rods causing the chassis to roll back a little, which is as good an indication as any. Click here for the video. Note, still no oil anywhere!

 
19 Sept 2010 Update  
 

Although 10 days have passed since the last entry, there's little progress that shows, and still more work required on the chassis. One totally unanticipated delay arose from a discovery that the slide-bar support assembly was modified at some point in the 1950s. Here's the arrangement I've settled on...


Loco No.34031 circa 1950

...and here's what the parts supplied in the kit could (almost) result in:-


Loco No.34072 sporting, what must be considered, the final arrangement

Discounting the parts removed from 34072, the major differences are as follows.

  • Cross-head mounted oil reservoir relocated to a lower position, below slide-bar.
  • Taller end-plate on mounting, with slide-bar lubrication reservoir attached directly to it.
  • Lubrication pipe runs are along and up & over the end-plate of the slide-bar support assembly.

Consequently, a fair bit of time has been spent contemplating how to fabricate the appropriate slide-bar support / attachment assembly. Here's a couple of views of what I've managed to achieve with a lot of filing and fettling using a length of brass 'U' channel:-

As well as (finally) attaching the slide-bars, the chassis now has (functional) mountings for the bogie and pony truck, as well as the body mountings added. Note the trailing wheel-set installed to check-out the plunger pick-ups. Also added is a sprung arrangement bearing on the middle of the centre driving axle, which provides a positive downward pressure to keep the wheels in (electrical) contact with the track.

 
22 Sept 2010 Update - Chassis with motion moves under its own power  
 

Several more battles were fought prior to the chassis running with the complete motion and picking-up the electrical power from the track that, with hindsight, I prefer to draw a veil over!!!!! I even manufactured a 12BA spanner to aid the assembly of the plunger pickups. Prior to running under its own steam, I decided it was time for a spot of lubrication.


Snapshot from video - chassis complete with motion running for the first time

Despite the wires from the pickups being unsightly twisted together with the motor wires, it ran rather well - click here to judge for yourself.

 
26 Sept 2010 Update - Bogie  
 

Once again considerable work and construction of parts from scratch in order to produce a passable representation of the bogie. Successful trial runs have taken place without any downward springing on the bogie, so currently it just comes along for the ride! The only suitable spring I have to hand is too strong and lightens the load on the leading drivers to the point where electrical pickup became erratic. This wouldn't be too much of a problem if I'd wired-up the electrical pickups on the trailing drivers. I suspect the spring will be about right when the additional weight of the body comes into play.


Snapshot from video - runs with the bogie attached

I've taken video of two trial runs: slow speed and high speed. The higher speed run was approaching top speed and gives an idea of the final speed of the loco; from the video; the scale speed is around 120mph - 5 fps actual. With these motors additional load has minimal affect on top speed, providing everything is free-running.

 
30 Sept 2010 Update - Pony Truck  
 

Yet again additional work and modification of the parts supplied in the kit were required to produce a functional representation of the Pony Truck. The problem here is that the clearances between the ash pans and the pony truck are pretty tight on the prototype. In model form more vertical movement is required so, for starters, the pony truck is not load bearing. Further, to negotiate tighter radius curves, considerably more side-swing is needed. To satisfy these requirements compromises are necessary, as far as the ash pans are concerned. Subtle changes to the ash pans are less obvious than chopping bits off the pony truck, in my view!


Snapshot from video - first runs of chassis complete with Pony Truck

At last, the chassis now runs as a 4-6-2 i.e. all the wheels! Click here for video of first trial of the pony truck.

 
6 Oct 2010 Update - Pony Truck & Ash Pan clearance  
 

With the chassis now functionally complete, I now need to sort-out the ash pans. The etchings provided in the kit are not very accurate in size and shape, so I've no reservations in modifying them further to achieve adequate working clearance for the pony truck.


Right hand ash pan tacked in nominal position

I started by tacking the two parts that form the firebox bottom and ash pan together, and then tacking the assembly to the chassis. There is a third part provided that represents the lower rear of the ash pan, but these severely restrict the side-swing if the trailing arms of the pony truck are fitted, as I have. Note the top of the assembly is tight up against the plate for mounting the cab and firebox portion of the body - see Body phase 1 (click here). Note there's some additional detail still to be added to the rear of the pony truck.

Trial runs with the ash pans in nominal position have been successful i.e. the pony truck didn't derail.

 
  (tbc)  

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