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Build A Cab Forward, 1
A Southern Pacific Mallet in 1:32 Scale

BY BILL TOMPKINS



WE USUALLY THINK of Southern Pacific's Cab Forwards as 2-8-8-2 locomotives but a few had 4-6-6-2 wheel arrangements. The first successful locomotives were class MC-2 (Mallet Consolidation) 2-8-8-2s. They arrived in 1911 and the Southern Pacific was so pleased, it tried some 2-6-6-2 locos with larger diameter drivers for passenger service. They became class MM-2 (Mallet Mogul) engines but they experienced frequent derailments until the SP replaced their two-wheel lead trucks with four-wheel trucks.

The idea for a cab-in-front locomotive resulted from problems on the SP's 150 mile Donner Pass line. It has 2.4-percent grades between Roseville, California and Sparks, Nevada The tracks climb over 6,400 feet to a summit of more than 7,000 feet at Norden. By 1909, thirty miles of snowsheds protected the line from heavy snows. It had many tunnels, too. When the Southern Pacific began to replace smaller motive power with Baldwin 2-8-8-2 Mallets, the smoke they discharged in the tunnels and snowsheds threatened to asphyxiate the train crews. The answer? Put the crew in the front and the smokestack in the back. In other words, turn around the locomotive.

My interest in Cab Forwards began when I was a boy and my father used to drive us through the mountains from Los Angeles to Mojave. The road ran along the tracks and, for miles, we would watch Cab Forwards climb and descend the grades. As my interest in large scale railroading developed, the Cab Forward was the natural choice for a scratchbuilt model.

I chose 1:32 scale because, in that size, LGB's 45mm Number One gauge track becomes an accurate 4 feet 8 1/2 inches, perfect for standard gauge. At the same time, my engine would be able to run on ARISTO-CRAFT and LGB layouts with 24 inch (1100) minimum radius curves so I would be able to take it anywhere.

I made my own simple 1:32 scale drawings of a Southern Pacific MM-2 and, as the basis of my model, I chose the mechanism from an LGB 2085D Mallet. The locomotive consists of two major sub-assemblies. Its running gear includes a modified LGB frame, the two motor units, pilot, rear deck, and lead and trailing trucks. The second sub-assembly, the superstructure, includes a detailed boiler and a cab with interior. As I discovered, and hope you will, modeling in 1:32 scale is a real pleasure.

My description will be somewhat general. It will explain my approach rather than offer a lot of specific construction details. Anybody about to tackle a project as sophisticated at this should already have a basic knowledge of modelbuilding techniques and sufficient plans and photos.

THE FRAME AND MECHANISM

Begin construction of the new model by disassembling the old one; remove the superstructure from the LGB Mallet. With the boiler, side tanks, and cab out of the way, you are able to separate the smoke unit, circuit boards, and wiring for inclusion on the Cab Forward. I wrapped mine in a plastic bag to protect them during assembly.

Use a hand saw to remove everything on the upper frame, the so-called footplate, except a flat bed connecting the two motor blocks. That will become the foundation for mounting the new superstructure. The model will consist of a series of subassemblies.

Build up the forward frame extension from Plastruct square tubing and sheet styrene. It extends from the forward motor block and supports the pilot. Photo 2 illustrates how I built it. And remember, since the mechanism now faces backwards, the rearmost motor block will now be the forward motor block.

By now, most of us know styrene cement has virtually no effect on LGB plastics. I experimented a bit and settled on Pacer Technology's PlastiZap CA for all assembly.

I scratchbuilt the pilot from styrene. It attaches directly to the forward frame extension. It has a scratchbuilt styrene coupler pocket, brass brake pipe, and a lot of nut-bolt-washer castings. The stanchions for the coupler release lever are brass turnings; the lever itself is brass rod. The "cow catcher" part of the pilot came from an LGB 2017 0-4-0 switcher.

I made no alterations to LGB's method of articulating the motor blocks and, consequently, it will negotiate LGB 1100 curves and 1200 turnouts (both a nominal two foot radius and the tightest commercially available). On the prototype, only one engine swiveled beneath the boiler whereas, on my model, both do. The frame extension and pilot swing with the front engine beneath the firebox and cab. It may be a compromise, but it works!

Similarly, the four-wheel pilot truck pivots from a swing arm and that, in turn, attaches to the forward motor block with a screw. Photos 3 and 4 show the construction. I used the pony truck from a Kalamazoo 4-4-0 for the pilot truck. At the time I built my model, the part number was 1002-3. I have no idea whether such parts are currently available. I do know you may still order the metal wheels I used as replacements for the large flanged, plastic Kalamazoo wheels. They come from Shortline Car & Foundry. I used wheels from the same manufacturer for the trailing truck.

Fabricate the brake rigging on the pilot truck from sheet styrene and brass rod. I used some brass bolts, too. I also added weight to the pilot and trailing trucks to minimize the possibility of derailment.

Build up the rear deck, the platform above it, and the steps from sheet styrene and McKean Models number 125001 styrene tread plate. Use brass rod for the handrails and brass sheet stock for the drawbar. As Photo 3 indicates, my drawbar has five holes for a variety of coupling positions, depending on where I operate the model.

Re-attach the motor blocks to the frame. Remove as much material from the LGB weight as necessary to allow the addition of air tanks. See Photos 3 and 4. Before proceeding, assemble and test run the frame and mechanism. Be certain everything works perfectly through curves and turnouts of all radii; if anything is wrong, now is the time to repair it.

THE BOILER AND CAB

Use 1/4-inch thick PVC tubing 2 3/4 inches in diameter for the boiler. The photos show how to splice the smokebox and stack from the LGB Mallet into the end of the boiler. Build up layers of styrene strip spacers until you have a snug fit, then secure the smokebox with CA. Then trim and notch the boiler and smokebox to clear the LGB frame and lead weight.

Use more of the same McKean Models plastic treadplate to build up the running boards. Sections from the Mallet's original side tanks make up the sides of the new locomotive's firebox. The rivet detail is crisp and pretty convincing. Add styrene sheet reinforcement to the back side. I represented large staybolts with brass screw heads, then mounted the boiler to the frame with six screws. Two went in front, inside the firebox, and four secured the boiler at the rear. If you look closely at Photo 3, you may make out the six screw holes through the write boiler tube.

A way to make the domes caused no end of contemplation until I arrived at a very simple solution. I filed 1 3/8 inch diameter PVC plumbing pipe caps to shape as I rotated them by hand, then sanded them smooth with emery paper. To create a smooth arc joint with the boiler, I roughed in the curves with a half-round file, wrapped some sandpaper around a scrap piece of PVC pipe the same diameter as the boiler, and sanded the domes to a precise fit. That finished the basic boiler and, altogether, it was probably the most difficult sub-assembly of the model.

Next, build the cab. It will be a separate sub-assembly. Use Evergreen .060-inch thick styrene sheet for the walls and Plastruct angle stock inside to reinforce the corners. My roof is removable and .060-inch thick sheet styrene works perfectly for it, too. Cut a pair of ribs to serve as roof formers from the same sheet. To curve the roof, carefully heat it in the oven until it just begins to soften, then form it into the approximate radius of the roof formers. Cement will hold it in place.

When you have completed the shell, cut exterior "veneer" walls from .020- or .025-inch thick styrene sheet and punch in rivets. A Northwest Shortline rivet tool may work or you could make your own. I punched my rivets individually, by hand. Laminate the exterior walls onto the shell and your cab will look as though the shops had fabricated the cab from thin sheets of steel.

In a model as large as this, a cab interior adds authenticity. I built up most details, such as seats and hardware, from sheet and strip styrene. Use the LGB Mallet's backhead. I enhanced its appearance with a variety of commercial castings and scratchbuilt styrene details such as gauges, valves, throttle, brakestands, and brass rod piping. My backhead shows partially in Photo 3. It is an assembly separate from the cab itself and I painted it and attached it after I painted the inside of the cab.

After painting the cab interior, add doors and windows from clear acrylic. Build up the door frames and window sash from styrene strip. I made my doors operable by hinging them with brass wire. Paint the doors and window framing before installing it. I illuminated my cab with the bulb and bracket from the LGB Mallet; cut the bracket off the Mallet and mount in on the Cab Forward's firebox. Make up a roof vent from sheet styrene and use brass rod for the handrails.

You must also build up a headlight and number board assembly. I used 5/8-inch diameter PVC pipe for the headlight and styrene sheet for the triangular number board extensions. Drill holes through the headlight casing into the open number board extensions to allow a bulb to illuminate the number boards. Make the number boards, headlight lens, and classification light lenses from clear acrylic. Make up the large number boards at the top of the cab from sheet styrene and use clear acrylic faceplates for them, too. Remember to wait until you have painted the model before adding the clear acrylic parts. I turned my own bell from brass and mounted it in a brass and styrene bracket. A suitable bell may now be available from Cal-Scale or possibly some other source.

NEXT TIME...

That should keep you busy for at least a couple of months. In the next issue, we will complete the Cab Forward by adding details to the superstructure, building the tender, painting, and lettering.



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