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Friday 27 September 2019

0 Gauge Class 33 - Scratch Built

Class 33 33202
I tried to recall how I came to scratch build a Crompton Class 33 diesel locomotive. It is probably the most complex and time consuming modelling project I have undertaken to date.

Without doubt the styling proportions of the 33 make it a pleasing sight to my eye, compared to other Southern diesels. I was also attracted to the r.t.r. Lima 0 gauge offering, which is remarkably inexpensive to buy off eBay - around the £50 mark. But, the reviews I read revealed it to be woefully inaccurate dimensionally, so bad that some serious 'cut and shut' work would be necessary to bring it into line with the prototype.

With a 3D printer to hand I decided to design and make one. First point of reference are a drawing and photographs. There is a partially dimensioned drawing in a book that I own -  Diesel and  Electric locomotives of the Southern Region by N. Pallant & D. Bird. I copied this and enlarged it to 7mm scale and from this most dimensions could be measured. There are also drawings available from the web. Despite this some fine details are missing or obscure in the drawings so, recourse to the web for photographs was in order. Most are distant profile views like in the example above. It required much time to find suitable close up and side views to work from.

The bogie's were tackled first as I considered these to be the most difficult items to design and make, firstly because of the large number of details on them and secondly the precision fitting of motor and gears, particularly optimum gear meshing. Before starting the design I had to source wheels and motor & gears. All were eventually found on ebay. The wheel sets are Peartree Engineering 3' 7" finescale diesel wheels. These do not have locating spigots but use bushes mounted on the axles and fixed to the bogie frame. The motor and gear set are by an unknown manufacturer. There is a risk the motor would not be adequate and even having made the bogie and run successfully there is still uncertainty over whether it will pull the body weight and train.

The bogie is essentially two separate parts screwed together. An inner part is the motor frame containing motor, gears, wheels and pickups. If there are issues with the motor/gears performance needing change then only the motor frame would need to be redesigned for a different motor (in theory). The outer part of the bogie is the decorative part.

The parts were printed in black, which had an undesirable effect of hiding the details from sight. Weathering was applied with brown and beige pastel scrapes to highlight the details. Some mechanics of the bogie were omitted from the design either because they were too fine to be printed, could not be easily discerned from drawing or photo or, would not be seen from normal viewing angles.I think most details are included though.

In the above photo we can see the motor mechanics, noise suppression capacitor and electrical pickup, which rubs on the axles. One of the wheels on each axles is insulated. The metal can of the motor connects to the one side of the armature coil and the pickup for the power return. The power feed is collected from the other bogie.
The other bogie with its power pickup is shown above. The design and build is identical to the motorised bogie without motor/gears fitted.
And here are the two bogies alongside a scale drawing. Not yet obtained track so am using two lengths of Hornby 00 gauge Super 4 track for now

At the end of the day the cost will be about the same as a second hand Lima 0 gauge model. At least mine will be more accurate and making it from scratch fulfils my creative need.

To Part 2.

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