D&SL 2-6-6-0:

The first standard gauge mallet type steam locomotive to be built in 1:20.3 is the work of George Konrad who was inspired by Barry Bogs' model of the same locomotive in 1:22.5 scale, Gauge 3. The prototype locomotive at right, built in 1916 by Alco's Schenectady works for the Denver & Salt Lake RR, a line absorbed into the Denver & Rio Grande Western in 1947, was a 2-6-6-0 compound with 55" drivers and exerted about 77,000 pounds tractive effort (hence the D&RGW's designation L-77). The L-77s were short lived on the D&RGW, all of the class being dismantled by mid 1952. As an interesting side note, some of the L-77 class began life in 1908 as 0-6-6-0 mallet compounds for use in both hump yard and helper service and were later equipped with a pony truck for better tracking. On the D&SL, or "Moffat Road," they were heavy freight power; but on the Rio Grande, they were midget mallets in comparison with the road's massive simple articulated L-131 2-8-8-2 and the two classes of 4-6-6-4 Challenger sported by the Grande. Like all Rio Grande standard gauge steam, save for a lowly C-28 class 2-8-0, none escaped the scrappers' torch.

Research & Resources:

George's D&SL 2-6-6-0 is his first effort in 1:20.3 standard gauge and is intended for outdoor operation around 370 feet of dual gauge garden railway with about 7'-6" minimum radius. Since there are no readily available prototype drawings for this particular locomotive, dimensions for the F scale model have been approximated from several different sources: (1) the D&RGW's own folio drawing, which provides rudimentary wheelbase measurements, (2) a set of elevation and section drawings for the predecessor 0-6-6-0 which some of the L-77s were based upon, and (3) the O scale builder's drawings that were made for Pacific Fast Mail's imported brass O scale model (kindly provided by the current owners of the non-defunct PFM product line). Several of these drawings are reproduced below:

George's model is a combination of scratch building and adaptation. The tender, tender trucks, boiler, cab, and lead truck are all scratchbuilt from either brass, styrene, or urethane castings based upon styrene masters. The chassis however is the result of regauging two brass and steel Accucraft 1:29 scale, Pennsy K4s Pacific mechanisms with new axles, frame spreaders, frame extensions, and cylinder halves. It is on this part of the project that I have had a prominent role, George having asked me (Dave, your host) to make the Accucraft mechanisms work and to look like a small mallet rather than a couple of of truckless 4-6-2s! But more on that below.

The Tender

The D&SL 2-6-6-0 tenders were modest rectangular affairs, carrying 22 tons of coal and 9,000 gallons of water, and riding upon 5'-11' wheelbase Andrews trucks. George's tender trucks are cast in urethane from styrene masters, and are reinforced with music wire embedded within the casting. They are not sprung, but do equalize, pivoting about the truck bolster. Wheelsets were originally of my offering, now available through my friend Don Niday. The tender itself is built up from 0.040" styrene sheet, the sides of which were marked for lines of rivets, predrilled, and then hundreds of small Peco brand track nails were inserted into place. Provision has been made for a Phoenix Sound System (of course, George is one of their dealers).

Pony Truck

Since no detailed plans were available for the lead truck on the D&SL 2-6-6-0, a compromise solution was to use scale drawings for a built-up lead truck of roughly the same design. One which I happened to have on hand came from a late 19th century Southern Railway G-Class 2-8-0. After the original Southern Railway linen blueprints were scanned, I imported their raster image into AutoCAD, traced them, and then generated separate part drawings for each part of the truck. Since this was not to be a casting pattern, but a one-off model, each part was cut at 100% exact scale size from either brass sheet or brass bar stock on my Japax Wire EDM. I also supplied the 30" wheels and axle, the former adapted from 7/8" scale steel wheels made by Gary Watkins of Sierra Valley Enterprises. These were spot on with respect to their OD and required only a bit of facing on the lathe to make them appropriate for F scale. The remaining assembly work George did in his own workshop, including the addition of the radius arm.

The Chassis

The biggest challenge with George's project has been how to come up with a plausible chassis without going to all the trouble of building everything from scratch. The solution that George arrived at was to use two 1:29 scale Accucraft Pennsylvania Railroad K4s mechanisms since their axle spacing between the drivers was very, very close to the L-77's 5'-0" in 1:20.32. This is the point at which I got involved in the project, and my job has been to regauge and modify them into the high and low pressure units of a mini-mallet.

I began by drawing both the Accucraft frames and frame spreaders (as is) in AutoCAD and then doing the same for the 2-6-6-0's frame, cylinders and crosshead guide spreaders in both elevation and section views (or at least as best as one could estimate these from the somewhat sketchy 0-6-6-0 drawings posted above). The challenge has been both to estimate the missing pieces from the D&SL engine and to figure out how the narrow (.080" thick) laser cut frame halves of the Accucraft model could be modified to look like the 4.5" thick bar frames of the prototype--which are both longer in some places, shorter in others, and generally ride higher than the Accucraft frames.

Boiler & Cab

Since

Last update: 10 June 2008