CN Woodchip Car - 879 000-series Updated 3D Model

I'm glad to announce CN 879000-series woodchip car model has been redrawn completely for scratch and soon to be ready for a first 3D print test.

Improved design build upon what was learned from 878000-series, meaning a one part complete shell including brake details on the underframe, separately printed car ends with platforms and brake details (housing, chain, rod and fulcrum).

The weight will also be concealed under a 1mm thick styrene floor into a recessed space in the shell. I know this is a compromise, but were aren't building a real 1:1 car which has the correct weight to track well on rails, but a plastic shell that needs additional weight. I've sacrificed the underframe because I believe most people prefer a neatly rendered visible interior in an open car than a perfectly prototypical steel structure under the floor. Certainly, if this car was in O scale instead of HO, that would be another story.

Among various differences from my first model of this series are strengthened car ends. My pre-production model suffered from breakage there and I felt it was a design flaw. Now, the end bottoms are an integral part of the one-part shell, helping to align the ends but also providing more material to support the buffer beams that protrudes.

I also added molded on stirrups. I know they aren't for everybody, but I do believe many will find them easier to work with. However, they can be easily upgraded with metal ones easily.

CN Woodchip Car - A Proof of Concept

Yesterday, a few test prints were made to confirm if printing ladders and brake platform directly on the model was both feasible and satisfactory. A big thanks to Guillaume Pedneault for providing these samples with helping me with the final design.

Car ends with ladders and brake apparatus (credit: Guillaume Pedneault)

Be aware the sample weren't cleaned out and got only a quick coat of red primer to make details pop up. I was quite happy to see most details printed well, including the brake wheel and fulcrum. However, we have serious doubt the small chain would survive under normal circumstances when cleaning the model. This will have to be addressed with some kind of support under the chain itself. I still have to figure how it will be done to stay unnoticeable. I could have omitted this detail altogether as I did on my original pre-production model, but it definitely had a level of realism that should be appreciated by modellers.

As for the trucks, I've yet to figure out a few things about NMRA standards and recommended practices. Their information on journal dimensions seems to be a little bit weird and I tried comparing them to Accurail, Rapido and WalthersProto trucks... none of them matched the standard.

Barber S-2 truck sideframe (credit: Guillaume Pedneault)

That said, the printing went well. I can still see a few areas that could be greatly improved on the trucks. However, the person helping me with the prints gave a few good hints and it paid off. The springs looks good even if the sideframes aren't completely cleaned. The cast on lettering is always surprisingly good. Barely readable, but still there. The big challenge is making these trucks run freely.

Meanwhile, I working on a completely new 3D model of 879000-series woodchip car. The original 3D file was full of artifacts due to me not knowing what I was doing. Fortunately, with a better grasp of my tools, it's far easier. Ditching the millimetric template in SketchUp and learning a few new commands is making the work faster and better.

CN Woodchip Car - Barber S-2 70-Ton Trucks

I've been trying to source parts for my various modern freight car projects, however, these are sometimes hard to find when you look for nice ones or simply hard to source when you want to buy them in bulk. Given the actual precarious conditions and given it would be foolish to count on unreliable sources, I've decided to design my own version of Barber S-2 70-Ton trucks equipped with roller bearings.

Working with photographs, drawings, NMRA standards and recommended practices and a few HO trucks from various manufacturers, it took me about half a day to come up with something both pleasing and, I hope, will be mechanically sound. I wouldn't have never believed there was so much variation with the S-2 truck family. Honestly, it seems none are born identical. For this reason, I tried to reach once again an acceptable compromise by matching my work as close as possible to what what photographed by Justin Babcock on the prototype a few years ago. Bear in mind it is highly possible this wasn't the freight car's original truck or that great discrepancies can be found among the fleet due to 40 years of maintenance and repair. However, what I design should be quite right at capturing the feel of the real thing.

The model will probably require a few adjustments after conducting rolling tests. For this reason, two designs will be tested. The first is made of two sideframes and a bolster that are glued together. The second one is a 1-part complete truck.

CN Woodchip Car - Third Pre-Production Model

The last two weeks have been spend redrawing completely the 878000-series woodchip car to get it right. It was also the perfect occasion to think about how it would be printed, the level of details and how the thing can be assembled by modellers with various skill levels ranging from newcomers to skilled craftsmen.

This new pre-production model will feature 3 main parts: a 1-part body with sides and underframe details and 2 end parts including ladders and brake platform. Gluing them together will provide a complete model.

The modeller will have to add a few grabirons, glue the brake wheel, cement a brake rod and install standard Kadee couple boxes and S-2 Barber trucks. Ladders, brake housing, brake plaform and fullcrum are already printing and don't require assembly. Same thing for underframe brake reservoir, valve and other such things. I've also made the stirrups molded directly on the shell. I'll see if they are sturdy enough to be worth it, but from what I've seen, they should be fine. That said, more detail driven modellers will have the option to remove the stirrups and replace them with metal ones if desired.

As for brake rigging, I've provided none. The reason is simple: most modellers don't care about that while the ones that do care generally prefer to add the details themselves according to their own personal standard. So instead of providing a half-baked solution to both type of modellers, I prefer to offer a decent underframe upon which one can do exactly what he wants. I'll probably provide a brake rigging diagram for guidance. Also, holes in the underframe are provided to install air lines.  

Weight was certainly a problem for these open cars. While a neat underframe is always cool, these cars can be often seen travelling empty on layouts. Thus, I feel the interior should be as accurate as can be. It means I've design a recessed floor in the underframe which can hold a steel weight that brings the car within NMRA standards. The weight is then covered with a 1mm styrene sheet to hide everything and provide a smooth floor like the prototype.

For couplers, I originally designed quite complicated and nice boxes, but the thing is 3D printed resin can be brittle when you drive a screw in very thin-walled parts. Most of them broke on my pair of preivous pre-production models, so I've been advised to simply swith to Kadee. To be honest, the difference is barely noticeable, even under closer inspection.

So now I only need to get the printed version of these new pre-production models. As you can see, I've had to make a few compromises to take advantage of technology instead of fighting against it. In some sense, it has made the model easier to assemble and sturdier, which is a good thing. I know a few people will want many cars in their fleet and assembly should be relatively straightforward. I'm also happy the model can provide a good starting base for a fully detailed model. I took care to have coupler drawbar supports were required for this reason.

CN Woodchip Car - Start From Scratch

I've often wrote about the inability of SketchUp to manage sub-millimetre dimensions. The software is now showing its age, having not been designed to take into account 3D printing back in the early 2000s.

The thing is that as you add parts to your model and merge together shape, small discrepancies creeps here and there. At first, it is unnoticeable. If you enter 0.500mm then you really get 0.500mm, but after a few merges of various components, that becomes 0.498 and some weird angles start to appear. What used to be 90 degrees, will misalign itself on other component. It has been noted by users on SketchUp forums the software have a hard time dealing with very large and very small dimensions.

I've redrawn the model 3 times in the last few days, often from scratch, but always ended up with the same discrepancies. I've worked with CAD softwares for decades now and I now I'm a precision-oriented kind of maniac in this regard. I can't stand odd numbers when dealing with plans and I know, after controlling several parameters, I wasn't the main source of discrepancies.

Most people would think it isn't relevant because most of these errors are several orders of magnitude smaller than what a 3D printer resolution could manage. That's true. However, it becomes a real problem when you try to merge elements together. SketchUp works with faces instead of volumes, so if "parallel" faces aren't really parallel, you can no longer deal with coplanar geometry. In my case, it made it almost impossible to merge together the underframe and walls. This is a big problem because drawing the model using independent components then merging them together later as you go along allows you to manage parts easier instead of fighting with a single part.

Main shell - Almost completed

My first reaction was simply to model the prototype by making it 100 time bigger. That way, I wouldn't have to deal with sub-millimetre dimensions. yet the same issues. Thus, I tried this morning to draw the model in meters. Each millimetre became a meter. In fact, 1.5mm is now 150m. By setting the drawing template to meter eliminates SketchUp inadequacy to address small dimensions. While the idea to enlarge the model was a good one, it only worked when I switched to the metric template (of feet if you draw in imperial units). Thus, the problem isn't about absolute numbers, but related to unit. If you draw 15000mm, you'll get discrepancies. But if you draw 15m, you get absolutely none. Lesson learned! Hope it will help peoples out there using SketchUp! And yes, I know several new intuitive 3D modelling softwares are out there. I'm just trying to make the best of what I have.

Main shell showing the floor depression hiding the metal weight.

That said, redoing the model several times was a good way to improve the design and I'm glad I did. I've reach the point I can redraw almost from memory. Many things have been simplified and I found a way to hide the weight in a way that will look nice when the car is empty while not scrapping all the underframe details. As much as I can, I feel this car must be as straightforward to assemble with being easy to superdetail for modellers wishing it. Maybe I'm wrong to try catering to two different crowds, but this is something worth trying to achieve.

In the next blog about this car, I'll explain how the model will be assembled using - I hope - cool graphics to demonstrate the design.