A Narrow Gauge 4-4-0 Part 1

Introduction
I am starting another long project but in addition to the "how-to-build" I want to demonstrate how to find generic characteristics of narrow gauge rolling stock and how to use those characteristics to build free form models.

My original subject was a C&S gondola, but further research revealed that a 4-4-0 would be more appropriate because one was not available.

What are Generic Characteristics?
Generic characteristics are the range of measurements derived from comparing dimensional data from several sources (plans, prototype cars, etc). What is sought is the range of measurements of car length, car width, car wheelbase and truck wheelbase from all these sources.   Typical designs use similar measurements but not exactly the same.

How to Find Generic Characteristics
For this concept to work, sources need to be chosen which express these generic characteristics. The subjects chosen can be any similar rolling stock.  Using one source that is atypical of the type of design will cause the data to be incorrect, as the extreme dimensions will suggest that these dimensions are typical when they are not.

Do you want to model narrow gauge in general, California narrow gauge, eastern narrow gauge, European narrow gauge? Whatever you chose, select the largest narrow gauge railroad(s) and consider their equipment as having generic characteristics. I use C&S and D&RGW as primary and then add any other railroads as I can find information on them. Choosing small railroads, where everything is built at random, does not give good generic characteristics. Sometimes the equipment of larger railroads have unique characteristics which label that car as belonging to that railroad.  Also watch out for one railroad having rolling stock from another.  All you end up with is two sets of the same data.

Yes, this is all a bit subjective but as you measure rolling stock or collect plans you'll find most have roughly the same dimensions.

What Data to Gather
What dimensions does one collect? The dimensions that give the item its general shape: length, width, car wheelbase, and truck wheelbase, plus its height, queenpost spacing, and sidesill thickness.

Sources for 4-4-0

For this project I used the following five sources. These were randomly chosen from my 4-4-0 file.

"The Colorful Eureka" Model Railroader, Dec 1997, George Sebastian-Coleman

"South Pacific Coast Railroad #3" Narrow Gauge and Shortline Gazette, N/D 1998, Robert Schlechter

"Ohio River & Western 3-Foot Gauge 4-4-0's - #9 and #10" Narrow Gauge and Shortline Gazette, J/A 1998, Edward H. Cass

"Nevada County Narrow Gauge #7 a 3-Foot Gauge 4-4-0" Narrow Gauge and Shortline Gazette, M/A 1997, Ed Gebhardt

"Southern Pacific Narrow Gauge Locomotives" Valley Car Works, Sheet #1

The first bits of data I need concern the engine wheel spacing and diameters and the layout of the tender. This is needed in order to look for a mechanism suitable for building the model. The drawings illustrate the dimensions which data has been collected from.

I took my five sources and wrote down dimensions.  Then I took the highest and lowest and used these as the range.  

The data collected can now be used to look for a suitable mechanism, but a few more dimensions need to be taken.

A Narrow Gauge 4-4-0 Part 2

Before a chassis is searched out, more dimensions are collected concerning the next major components, those being the boiler and the tender body.

Conclusion

The engine cab has been omitted for now, but it will need to be considered during construction.  Now the search for the chassis begins.

Using the Data
It is safe to say that no HO mechanism will fit the range of measurements exactly, so we have to decide how far off the mechanisms can be to still be useable.

Searching for an HO Mechanism
This search is based on the data collected in Charts 1 and 2.

Criteria for The Search
1. Focus attention on driver diameter and driver spacing.

2. HO 4-4-0’s are a possibility, but the driver diameter and spacing will probably be too small.

3. Any engine with the frame extending past the rear driver can be eliminated. This is usually where the electric motor is located and this area would have to be cut off to be useful. This also includes any engine with a rear truck or axle.

4. A 4-6-0 is possible because of no rear overhang, and the front driver may be able to be removed, leaving two drivers at a useable spacing.

5. A 2-6-0 is also possible for the same reasons as in #3.

6. Since HO is not quite one half the size of O, a perfect mechanism will not be found. Any mechanism chose will have more than one area of compromise.

The search reveals three possibilities: The Bachmann Harry Potter 4-6-0, the Tyco/Mantua 4-6-0 and the MDC Roundhouse 2-6-0. After acquiring a Harry Potter engine I eliminated it as a possibility as the cylinder and rods would have to be completely redesigned and built.

Now to see how the two chosen HO engine mechanisms compare the protoytypes.

Chart 8 Tender Measurements