D&RGW L-105 4-6-6-4
(2011-??)

The Denver & Rio Grande Western L-105 Challengers were built at roughly the same time as the M-68 Northerns and were designed to share a number of components. Both engines appear to use the same trailing, lead & tender trucks. Tenders are essentially the same as are the all-weather cabs. Both locos use Baldwin's own distinctive disc driver, the M-68 having a driver 3" larger in diameter than the L-105's 70" version. With their disc drivers, Commonwealth one-piece cylinder & frame castings, multiple bearing crossheads, roller bearing axles, and (later) overfire jets, these fifteen locomotives (#3700-3714) were the epitome of modern steam power on the Grande. All were sent to the scrappers by March of 1956, being replaced first by EMD F7s acquired during 1949 and 1950 and then by GP7s purchased by the Grande in 1952.

Doug's model of the L-105 represents the first batch of locomotives produced by Baldwin in January of 1938. They are different from the second batch (#3710-3714 arriving on the property in early 1942) with their Baldwin Disc drivers (the later engines had boxpoks) and prominent Elesco feedwater heaters. These Baldwin built challengers were well suited to the Grande's mountainous profile, developing 8,000 lbs more tractive effort than their lighter, Alco designed cousins on the Union Pacific. With the construction of the L-105 4-6-6-4, Doug has achieved another first in F scale: The first 1:20.3 standard gauge articulated locomotive. Well done, Doug!

With A Little (More) Help From My Friends

Having friends to contribute to a project as complex as a 1:20.3 scale standard gauge 4-6-6-4 makes all the difference in world. In the first place, Doug has the singular good fortune of a patron, Mr. Gary Bartlow, who commissioned the building of the L-105 as well as the four M-68 models. Gary now has the singular distinction of owning the most standard gauge models in F scale of anyone in the country. We hope to see Gary building a layout soon to run these monsters on! So far, eight different people are at work on or have contributed components to the L-105:

● Dave Queener of Cumberland Model Engineering (your host) is responsible for machining and assembling the 70" drivers, main & side rods, construction of the four wheel lead truck and initial CAD work on the L-105's lead engine unit.

Drawings for this project have come from several sources: First, Hundman Publishing's The Locomotive Cyclopedia--Volume II (article by Robert L. Le Massena, drawings by David Day) has been quite helpful in giving an overall view. Second, the Colorado Railroad Museum's Richardson Railroad Library provided prototype elevation and section drawing as well as several component drawings: front frame, trailing truck frame, main & side rods, and others. Finally, the lion's share of part drawings is coming from the Denver Public Library's Western History Collection. To these we should add drawings of the distinctive Baldwin disc drivers which were found in a late 1930s era Locomotive Cyclopedia. Additional help has come from a brass O scale model of an L-105 imported years ago by Max Gray. Here's a sample of some of our main resources:

The first order of business on my portion of the L-105 project was to complete the Baldwin designed lead truck. This same lead truck was, like the trailing truck and tender, also used on the M-68 4-8-4, the two classes of locomotive being purpose built by Baldwin to have many interchangeable parts. Since I did not have part drawings of the L-105 lead truck--only the elevation and section drawings above--about 25 hours of CAD work were required to trace and guesstimate the truck's design. 115 man-hours of machining and assembly work later, the first truck was finished by me in mid-January of 2011. This is only the second 4-wheel lead truck that I have built, the first being a somewhat stiff affair I filed from brass bits and pieces about ten years ago for a model of Little River Lumber Co. baby 4-6-2 #110 (see thumbnail above). By contrast, the L-105 lead truck is sprung, equalized, and features a spring-loaded centering device. Heart-shaped rockers for the centering device were deemed too fiddly for a rugged outdoor, operating model.

Most of the lead truck's brass parts were cut on my Japax wire EDM with a bit of additional mill work done on a Bridgeport clone. 36" lead truck wheels were supplied by Bill Brisko of Pacific Locomotive Works. Bushings and axles were made on my Monarch 10EE turret lathe. I'm confident that if I had it to do it over again, I would make the frame and centering components as casting patterns, and then have additional copies investment cast, which would greatly amortize the cost of so much machine work. Even so, I'm pleased with the results. My thanks go to Capt. Tom Mix (USMC, Retired) and master-modelmaker Kelley Morris for their suggestions, insight and superb examples from the smaller scales--and of course to Gary Bartlow for making this all possible.

L-105 Lead Engine Unit CAD Drawings

•  The Prototype--The L-105 was an early recipient of integrally cast cylinders, frames and valve gear supports. These massive steel castings were a honeycomb of pockets, undercuts and cores, including fully enclosed voids which served as air tanks. Designed to maximize frame strength and overcome one of the chief maintenance headaches common to built up frames, integrally cast ones overcame the natural tendency of bolted together frames & cylinders to work themselves lose due to vibration. Out of tram frames meant binds, hot bearings, worn bearing surfaces & misaligned cylinders. Baldwin subsidiary General Steel Castings provided these huge sand castings, pouring them in sand filled pits on the foundry floor. As an aside, the Pennsy's S1 6-4-4-6 duplex of 1939 World's Fair fame holds the record as the single largest one-piece locomotive frame ever cast. Sadly, General Steel Castings is no more and no foundry in America any longer has the capacity to do such large, open pours.

•  The Model--From a modeler's point of view, cast integral frames are difficult to reproduce due to their many cutouts and undercuts. It can be done (note the thumbnail at left of a 3/4" scale Big Boy frame); but even at that, most of the features of a cast frame will never be seen, so some degree of simplification is prudent. My design work on the lead engine unit for the L-105 reflects this reality. Starting with the prototype frame drawing, I first reproduced the lead engine unit in all its complex glory and then sought to simplify the model version from it. The image from my CAD drawing at right is that of the prototype without allowances for the model. A PDF version scaled to 1:20.32 and printable on size E paper (36x48) may be viewed here.

L-105 Side & Main Rods

My Japax wire EDM was kept hot during October of 2011 producing the four main rods, front side rods, and four back side rods for the L-105. These were first drawn in AutoCAD by tracing the original D&RGW blueprint provided by the Colorado Railroad Museum and then cut on two sides from 1" square brass bar. These were not casting patterns but the actual production rods. One of the lessons learned here is that it is more economical to make a casting pattern for each rod on the wire EDM rather than to burn every one individually since only about 4¾ hours of programming time was required for the three different rods but 36¼ hours were necessary for cutting all 12 production rods. Nevertheless, I am pleased with the results, and here are a few thumbnail pics of the results. Some milling remains, namely for the fluting on the main rods, and the fitting of bearings.

70" Baldwin Disc Drivers & Axles (updated 11-28-11)

•  70" Drivers for D&RGW L-105--Following the completion of the chassis for his four (yes, that's right--four) D&RGW M-68 4-8-4s,  Doug Hemmeter had 13 driver castings left over, enough for one D&RGW L-105 4-6-6-4 plus a spare. The M-68 and the L-105 were built at about the same time by Baldwin and shared a number of interchangeable components. Their drivers were nearly so, the M-68 using a 73" version of the unique Baldwin disc design whereas the L-105 had a 70" version. Some of Doug's drivers were partially machined by the late Doug Cockerham. I am now completing the job with my own scale 70" steel tyres, crankpins, ¼" axles, and quartering jigs.

•  Machining the Tyres--Doug's driver castings were originally intended for 73" OD tyres, but I am shaving them down to be compatible with the L-105's 70" drivers. My tyres are stock ones which I had made for me in Cape Town several years back using the Brandbright / Gauge 3 tread profile. Since that time I have begun using a new tread profile, same as we have used on our other F gauge wheelsets and for which Gary Watkins of Sierra Valley Enterprises deserves credit (this are his third generation of tread profile which works well indoors and out, with an approximately .074" flange height). I produce tread on tyres (or as in this case modify old ones) by plunge cutting on the lathe using a specially formed 1/2" square M-2 Cobalt steel tool thrust directly into a plain steel ring or disc of steel. Taking the cut slow and easy, the results are pleasing. Part of my setup is to use a 6 jaw Set-tru chuck--that way run out is kept to no more than .0005" and the concentricity of the tyre's bore and its outside diameter is kept true. I've been very pleased with the results I am getting from my 3000 lbs, 1946 Monarch 10EE lathe turning a Bison 8" 6 jaw Set-tru chuck.

•  Machining the Axles--Since this locomotive will be using four gearboxes provided by Barry Olsen of Barry's Big Trains, (see thumbnail at right) which uses a ¼" shaft with a flat on it, I made a dozen stainless steel axles to fit. The set up was pretty straight forward: Cut off, grind to length, place into a fixture in the mill, and cut the 1/8" x 1" flat onto the center of the axle with a four flute HSS end mill. Here's a few pics of this set up as well:

Last update: 8 December 2011