Wednesday, January 15, 2020

CN Woodchip Car - Update on Printed Prototypes

I know many people were eager to get more news about the CN woodchip cars project. It took me a while to start assembling the prototypes 3D printed by Bruce Barney last year due to lack of time, unforeseen professional projects and procrastination. However, I’m glad to announce the cars have been assembled, detailed, primed and painted over the last few years.

This assembly is not only a way to show people how the models will look, but also to seek arising issues and find ways to address them so the final product is, as possible as I can, flawless, sturdy and easy to assemble.

While the assembling procedure was quite smooth, I found out a few things that I’d rather change if I were to sell the models to others who want to build a fleet. I see a significant difference between what we can live with when scratchbuilding a single model for ourselves and what we find intolerable when trying to work with a “commercial” kit.

Issues I found are various but not deal-breaking. They will be easy to fix and yet provide a great finished model. I must admit once painted, these two cars could pass easily for good quality RTR models.

From a purely technical perspective, I’ll probably add some thickness to the parts, going from 1mm to 1.2 mm to lessen risk of warping. Straightening resin or 3D printed parts is an easy process, but it can be tedious and I quickly found myself annoyed. It must be improved. Also, while trying to keep the underframe structural members within prototypical dimensions and minimum 3D print design guidelines, I feel they must be sturdier. No a lot, but just enough to make sure breaking is unlikely under normal handling conditions.

In terms of assembly, I felt the grooves and tongues I designed to make for easy alignment of parts are inadequate. First, they are too shallow. Second, they lack tabs to make sure everything is perfectly square and aligned together. It shouldn’t have a major impact on the model, but expect some kind of tabs under the car. I’ve yet to figure out how to do it but it must be done.

Speaking of underframe, I 3D printed the brake apparatus (valve, reservoir, etc.) directly on the underframe. They look good, but I’ve yet to decide if it is a good decision. I feel it works well for most modellers and that it can be upgraded with pipes, wire and other such for prototype modellers. I’ve yet to decide on the level of details. Should I locate brackets and levers? I don’t know and I’m not sure if it matters. I feel the ones who will want these details are better equipped than I am to model these and I suspect a large share of modellers won’t care. However, I think the model must have provision for people wanting to go to the next step. It means, I’ll try to provide holes in the underframe to insert air lines. I’m not interested in cast-on details that can be seen from a normal point of view. They will be of no consequence for casual modellers and be a hindrance for people with high standards.

In terms of details, I found out some parts are better 3D printed while others should be photo-etched. Brakewheel platforms and end of car platforms should all be photo-etched for the sake of sturdiness. They can be printed in great details and be strong enough, but they are still fragile and can be broken during assembly. Photo-etched parts would be easier and faster to install while surviving nicely normal handling condition and providing a great level of detail.

As for ladders, I thought the 3D printed versions would be flimsy and they are not. Better, they look like the real thing, are easy to glue and the profiles are quite close the prototype. I believe using photo-etched ladder would remove a level of detail while performing minimally better.

I also plan to include a notch in the fulcrum so the brake rigging can be easily cemented and stay in place.

Another point is related to performance and NMRA standard. I design the car using correct model truck dimension and Kadee coupler pockets. On one car, I kind of tweaked the bolster height to fit the truck and it seems I made a mistake. To get the coupler at the correct height, I must add 3 Kadee red washers. This means my first bolster version was the right one. I’ll go back to it. The other car only requires 1 red washer, meaning the bolster height is quite right. I’m reluctant to make a change because I know various trucks may have different height due to manufacturer’s preference. At this point, better leave the fine tuning to the end user, like we all do with most of our RTR cars.

Another thing I found out was the height on the coupler pocket hole is slightly too high. About 0.2mm at most… It may seem trivial, but it causes the coupler to drop instead of being perfectly horizontal, impeding coupling performances. It will be addressed.

Finally, the screw holes for the couplers and trucks are not right. Trucks have pegs too thick and need to be sanded to accept a standard truck. On the other hand, the coupler pegs are too small, inducing unwanted wiggling and exaggerating the drop I mentioned before. All these are easy fix.

Other than that, I figured out one could easily assemble the model in an afternoon when all parts are cleaned and prepped. Doing an assembly line would significantly speed up the process, particularly if the locating pins and tabs are better designed.

I tested the car on the layout yesterday and they are sturdy and track well. Weight can be added between the underframe members or inside the cars if one is not afraid of seeing steel or lead from the top.

As for availability, I can pronunce myself on a date. I will have to address the few issues and print a new pair of "final" prototype before launching production and taking order. I've yet to figure out details about sale and distribution. All that with an extremely busy professional schedule in the upcoming months. Stay tuned!

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