Scratch-Building Model Railroad Steam Locomotives

Or, the convoluted path I took to tool-up…

Note: at the bottom of this post there are links to various threads and resources mentioned through the post. Over time, links tend to disappear, a sad fact of the internet. If any prove useful, make sure to pull what you need from them sooner than later…

From the time I was a teenager, I’ve wanted to scratchbuild steam locomotives. Back in that day (’70s), the material-du-jour was brass, and there was a whole sub-culture surrounding that material’s use in scratchbuilding, as well as a market for ready-to-run (RTR) brass models. In fact, most RTR were Japanese imports, painted gold or ‘brass-like’ to accentuate the use of brass. Such were out of my price range, and building them was out of my league. My dad and most of my relatives were what I’d call “industrial craftsmen”, carpenters, masons, welders; not that keen on the small, precision stuff. I pored over all I could find on the scratchbuilding part. Of particular interest was the Gordon Odegard series in Model Railroader in ‘82-‘83, “A USRA Mikado in Brass”. I was stymied at the tools list in the first article - reamers, taps, drill press, things that even then cost more than a high-schooler’s allowance would allow. Mr. Odegard actually did a good job of triaging the tool list, breaking it into ‘required’ and ‘desired’ items, but I still couldn’t see clear to assemble enough of them to get started. Probably for the best, as I really didn’t have the attention span to achieve single-thou precision. Heck, I wasn’t even cutting square for the simple woodworking projects I took on…

More recently, I’ve re-kindled the interest. Better-funded and better-armed with a sense of discipline and precision gathered in a 40-year aerospace career, I re-started my research. I also picked a first project, Denver and Rio Grande #168, HOn3 scale. #168 was until recently the park locomotive in Colorado Springs; a few years ago the city and the Cumbres and Toltec Scenic Railroad struck a 45-year lease agreement, where the railroad would restore it to operation. Indeed, they did just that, and they now use it in periodic excursions with a period-representative passenger car consist. The Friends organization put together a photo charter with #168 and the consist last year, which I happily rode and took a bunch of pictures to support the modeling project. Here’s one:

Measuring #168

The accomodating gentleman was holding the ruler for me to use as a measuring reference. The photos I took in this manner have proven extremely useful in both determining what things decorate the locomotive as well as their dimensions. Anyway…

I picked #168 because it seemed to be a simple first-project: no exposed Walscheart’s valve gear, small size, what looked to be simple shapes. I was able to find most of the appliances in the Precision Scale Company catalog (another side-bar: one of the dwindling number of HOn3 suppliers…), and the major parts looked to be within the scope of things described in the Odegard article. I was able to find an erection drawing of #168’s sister locomotive #169, which at this date still exists. It’s on display in Alamosa, Colorado, just about 40 miles from Antonito where #168 now lives. The drawing had an ‘exposed frame’ side-rendition which was very helpful in developing an understanding of that obscure part. Interesting, with access to all this information I’m still short a few renditions of various parts of interest; hmmm, maybe another trip down to Antonito???

Kept digging for more, came up with reference to a ModelTec magazine series on the construction of a live-steam version of #168, for which I’ve obtained scans of the associated drawings. Also of great utility has been Jerry Day’s recent book, “Rio Grande’s T-12 Locomotives and the Return of the 168”, with a bunch of really good photographs, including of various stages of its restoration. It’s hard to not turn such research into its own hobby…

With the confidence of a do-able first project, I started assembling tools and doing preliminary design. First up was the frame, respecting the order of things in the Odegard series. The essential operations were cutting, drilling, and filing small-gauge brass, not too hard. I started to assemble tools and materials, but was waylaid by the discovery of on-line cut-to-order metalwork concerns. Making a long story short, I ended up designing the frame with a 2D CAD tool, LibreCAD, and getting it cut to specification by OSHCut. Beautiful parts, only a few minor imperfections from laser sparking, a lot simpler to make than the cut-n-file endeavor outlined by Odegard. Here’s a picture:

OSHCut and ScaleLink Parts

From top-to-bottom: 1) ScaleLink drivers; 2) OSHCut frame with ScaleLink hornblock bearings; 3) OSHCut frame; 4) siderods; 5) smokebox, boiler, and firebox blanks, along with the smokebox front.

Okay, a few back-stories:

Not to be daunted by the siderod snafu, I was pretty stoked with these first parts. However, daunt-ness was encountered about this time in researching how to fabricate the steam and sand domes. Ok, brass rod, turned maybe on my drill press (not a great idea, as it turns out…), but then there’s that pesky curve in the bottom to accomodate the boiler diameter. Did some googling and found a video of a fellow cutting that curve in a lathe with a fly cutter. With that tool, you mount the material in the toolholder and the cutter in the lathe, start the cutter spinning and slowly feed it into the butt-end of the dome. Hmmmmm……

So, a lathe was looking inevitable, as I wasn’t finding the exact domes in anyone’s dwindling collection of castings. Alternatively, I started to look into 3D CAD-ing the parts for out-sourcing (not to OSHCut, they don’t do 3D parts…), which took me into the labyrinth of 3D modeling. I’d previously done some work with Blender so the concepts weren’t totally foreign, although I could never fully comprehend the FreeCAD toolboxes. What I did run into that felt intuitive was OpenSCAD, a script-based parameteric CAD tool. Instead of shaping stuff with a mouse, you write a script containing cylinder, cube, and other primitives. It clicked right away for a career programmer like me, and I haven’t used anything else to date. Steam and sand domes turned out to be trivial in OpenSCAD, just layers of cylinders. Even the boiler interface cut was easy; subtract a cylinder of boiler dimensions from the bottom of the dome:

OpenSCAD Sanddome

The highlighted code does the difference between the stuff of the rotate_extrude starting at line 42, which draws the basic shape, and the cylinder at line 49, which is subtracted from the shape to make the boiler curve. The subtracted cylinder is displayed in green here, but does not show up in the finished part. Yeah, not everyone’s cup of tea…

Anyway, with two CAD models of domes, I decided to see how Shapeways would print them. I ordered them printed in their “Fine Details Plastic”, and they look nice, but I was surprised that they were translucent. Turns out that’s an artifact of resin printing, which I’ll be talking about more in a later post.

Thing is, those two itty-bitty domes cost $10US each, and with shipping the whole thing cost $33US. After the fly cutter video, that got my attention. Printing even just the appliances was going to cost quite a bit. That’s when I started to look into 3D printing…

I’m going to get into my discoveries of 3D printing applied to scale modeling in later posts, but there are three prior projects I want to point out. These helped me develop a perspective as well as provided specific tips:

If you’re looking to take on 3D printing in your modeling, I think these three threads are definitely worth devoting your time to reading.

Resources

#3d printing #scratchbuilding #HOn3 #168