Using a computer to design models O
kay, I’ll admit it. I’m cheap. Not frugal, penny-wise or even thrifty. I’m as cheap as they come, possibly even a tightwad. Consequently, I didn’t want my ex- periments with 3-D printing to involve ex- pensive licensed software. 3-D computer aided design (CAD) software packages can run to the thousands of dollars, hardly a good start for a cheapskate like me.
While I am certain there is a ton of value in the professional packages, I’m not certain a single designer of mostly squarish stuff re- ally needs all that value. If you’re willing to shell out for one of the professional pack- ages, you should be able to generate a printable file straight from the package. I was willing to settle for a few extra steps in exchange for low cost software, and so I set out to find appropriate free or nearly-free software. I immediately came across Google SketchUp, which has a free version as well as a pro version. So far I’ve not needed any of the pro features. I found this program remarkably easy to learn, if fact, it’s now my CAD package of choice due to the expressive language for in- putting data. There are some excellent video tutorials, including one on precise di- mensions that is required viewing for rail- road modelers. In SketchUpI use the architectural tem-
plate, because it’s set up in feet and inch- es. I always work in full size and scale it down to HO later. SketchUpseems happi- est working with big dimensions, and will introduce weird artifacts if you ask it to work with small fractions of an inch. You will also want to enable the Utilities menu, so that you can force the creation of “faces” (click on Window/Preferences/Ex- tensions/Tools Utilities).
The other key to working successfully
with SketchUp is to break the model into Groups or Components. For example, on my passenger car, the roof ends, windows, body sides and body ends are compo- nents, while the central section of the roof is a group. Groups and components en- able you to export a portion of the model and verify that it can be printed. They also enable you to reduce the complexity of the displayed model, enabling you to select only the element you wish to work on, as well as speeding up the display. To be printed, a 3-D model needs to contain volume. Walls are actually two sur- faces with a space between them, rather than a single surface. The enclosed vol- ume has to be “water-tight.” That is, there can’t be any openings in the surfaces that would enable water to pour out if you put it on the inside.
The second major requirement is that the surfaces all have to be oriented the same way. SketchUphelps with the orien- tation of the surfaces by coloring the inside faces blue (by default) but doesn’t offer much assistance with water-tightness. Fortunately, a $20.00 program called Accutrans can identify problems with wa- ter-tightness and can also correct face ori-
RAILROAD MODEL CRAFTSMAN
entation as well as scale the final product to HO scale. Sadly, Accutrans doesn’t read Collada (.dae) files, which is what the free version of SketchUp can produce, so I found Meshlab, which is free and can not only translate from .dae to one of the Accutrans formats, but will also turn all the surfaces into collections of triangles, which the 3-D printer also needs. Thus, we have a little three-step dance to export a model ready for printing.
1. In SketchUp select File/Export/3D Model/Collada (.dae) 2. Switch to Meshlab and select File/New Project. 3. Now select File/Import and find the exported file. 4. Select File/Export and save file as .stl 5. Switch to Accutrans. 6. In Accutrans, select File/Open and find the .stl file you exported from Meshlab. 7. Select Tools/Check for Watertight Meshes. If you get an error, explore the model, looking for highlighted holes. 8. If everything’s okay, select File/Save with Options. 9. Set the output file type to .stl 10. Choose the scale factor by dividing 1 by your scale (eg. ¹/₈₇.₁ for HO, ¹/₄₈ for O, ¹/₁₆₀ for N). Depending on the printer, you may also need to convert to centimeters. 11. Click copy X to YZ and Save.
Okay, it’s not exactly three steps, but it still goes pretty fast for a smallish model. I have tried two services that are set up for high-volume, low cost stereo-lithography,
Shapeways.com and
Ponoko.com. Shape- ways was first, and frankly Ponoko is good, too. I have found the customer service from both of them to be outstanding. With both services, you simply sign on with a username and password, then up- load your file. For Shapeways, you can se- lect the units of the uploaded file (which is inches if you followed the steps above); on Ponoko, the default units seem to be cen- timeters. The service checks it over and gives a price, which depends on the vol- ume of material used.
For model trains, we’re looking for the highest detail and smoothest finish possible. As I write, this is “Frosted Ultra Detail” for Shapeways and “Superfine Plastic” at Ponoko. Choosing them will refine the price. Since prices vary by volume of material, you’ll want to make your parts hollow and walk the fine line between durability and cost. You also need to be aware that if parts are too thin they will not survive the printing, cleaning and shipping process. The minimum thickness, called the “mini- mum wall thickness,” is defined for each of the materials. Even if you maintain mini- mum wall thickness throughout the model, however, Shapeways or Ponoko may refuse to print it if they feel it will be too del- icate. So, err on the side of durability where you can.–RÉNE GOURLEY
er Red straight from the bottle after comparing all my reds with my Turkish Rouge sample. In a satisfying way, the color of the model depends heavily on the light under which it is viewed. The lettering was drawn in Corel-
DRAW®, working from some distant shots of CA coaches along with a crisper Grand Trunk car that seemed to exhibit similar lettering. From this lettering, I had All Out Graphics pro- duce dry transfers, which I rubbed down on the letterboards and on the sides. Despite the care I took to get this right, it doesn’t seem that the Canada Atlantic car shop crew felt the same way–the photographs of their passen- ger equipment rarely show the same lettering style twice. The lining was a nightmare. At first I thought I would use a paint pen from Sharpie.® While my initial tests on scraps went fine, I couldn’t manage a consistently fine line on the model. I wound up stripping the car side and “taking a mulligan.” (Golfers know what that means.) The successful tech- nique employs a colored pencil and is convincingly understated. When you see photos of CA cars in the nineties and early 20th century, the lining is barely there, and colored pencil accom- plished this effect nicely.
Onward
In the end, the car took me more than two years to complete. Looking back, it’s hard to understand why. It’s not as if I had any other major projects getting in the way, apart from a few experi- ments with 3-D printed freight car trucks. I seemed to spend long stretch- es at the computer and much shorter periods with knives and glues. Perhaps it was the periodic delays as I waited for parts to get printed or laser cut that made progress so slow. I also recall sit- ting down for some traditional model- ling sessions and feeling that my hands weren’t as practiced as on other mod- els. Maybe it was because I was never fully convinced that I was building the right car.
Whatever the reason, obtaining my model of Canada Atlantic No. 2 was an interesting journey. Now that I have the techniques and some of the com- puter files, building a mainline passen- ger train feels well within reach, even at my relaxed pace.
But first things first. The town of Pembroke was the end of the branch, and there are years of modelling to go before I will need to consider a main- line train. In the meantime, 3-D print- ing is going to continue to evolve, get- ting better and cheaper, and enabling all of us to build trains that are limited only by our imaginations.
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