3d printing a train

I’ve been inspired by the Warmachine Resurrection League scenario, “Derailed.” The terrain layout calls for three railcars, measuring 4×12 inches. Each railcar contains an objective, and must have a 4-inch doorway on each side, like a box car. I’ve decided to make up an armored railcar for the scenario, and let my resin printer do some heavy lifting.

The end, first.

I’m going to be honest – I overestimated what the printer is capable of. I’ve got an Elegoo Mars 4 DLP, which is a perfectly good resin printer. I really like the level of detail you can get with it, and it was plug and play. I ran into trouble segmenting the print job into manageable sizes and making the pieces fit. I didn’t expect the properties of the resin to be troublesome. Had I limited myself to just printing solid blocks of material it probably would have been fine. I tried some new things, hollowing out models, adding holes, and most importantly, switched resin types part way through the job. I’m going to detail out the path I took, what I learned, and what I’m going to do in the future on similar projects.

Prototype 1

Source material and first drawing.

I started by looking at real life images of railcars used during the second World War, and comparing them to railcars in the Iron Kingdoms. I also looked at scale model trains (O-scale), and some 3D print files from various sites. I based my design off some Flames of War models, upsized them to fit the Iron Kingdoms, and scaled back on some of the normal detail, replacing it with Iron Kingdoms styled details.

First drawing

Blender as a design tool

I’ve used Solid Works, 3DS Max, Fusion, Creo, and other programs. Most of my experience was through school, work, modding video games, and some other crafting projects. Fusion was my go-to for the last few years, but my account was free for too long, and I’m blocked out by a paywall. That’s the problem with cloud-based tools on the ether: they eventually dissipate. I decided to give Blender a go, having tried it out many years ago. It is so much better than I remember, and actually a decent tool for this type of work. It isn’t as powerful as a parametric CAD program, but it still manages to do what I need for cranking out a 3D model.

I did have to jump online to run some tutorials. I don’t recommend the donut tutorial by the blender guru. That dude is probably a good designer, but not a great instructor. Instead, I recommend Grant Abbit’s tutorials. Grant Abbitt – YouTube. I really enjoyed the beginner series where he walks you through making a monster looking at a dude looking at the monster. From there, he has some 3D modeling tutorials and others. His teaching style is solid – he repeats important parts, gives you an indicator of when you should pause and try things out, and then moves on with the project, always building on an idea. It’s solid work.

First test

The heaviest block of resin I’ve ever printed.

I started by cutting my model into segments that I thought the printer could manage. What I didn’t take into account was the raft on the bottom of the model – it’s larger than the model itself. That means if you plan to squeeze two-inch wide models on the plate, it’s actually going to take like two and a half inches. If you’re modeling with multiple pieces on a plate, you can smerge the rafts together. In this case, I had to print these two items separately, because they wouldn’t fit on the same plate.

The raft is the pink bit with holes that sits on the build plate.

Not that it’s a bad thing. I want the top and bottom to be separatable. But there were other problems. Note the model top and base don’t sit flush. That’s because my alignment plug isn’t sitting in the hole properly. In the future, I drop the idea of alignment plugs (even though I do eventually figure out how to scale them properly). More on this later.

Second test

The next segment is another part of the car’s top. I wanted to see if I had the alignment correct; and I did not. I cut into a model with a plug, using a Boolean modifier in Blender. That made a hole. I scaled down the plug to 99%, and attached it with a Boolean modifier on the joining side. When I fit the two segments together, they didn’t fit.

My solution was to take a cube, fit it with holes, then set up another cube with plugs varying in size from 95% to 98%. I’d test them out, and see what worked. Turns out, 95% is about right. Not too snug, and not too loose.

Alignment plugs being tested for sizing.

Plugging away at it

At this point, I was feeling pretty confident that I was getting things right. However, my cleaning solution was leaving behind enough resin residue to leave a white powdery looking effect on the model after curing. Additionally, I ran out of the resin that I originally purchased, and made a switch. Not wanting to deal with isopropyl alcohol anymore, I opted for a water washable resin.

New problems

This led to some more problems to solve. The water washable resin pulled away from the supports easier than the standard grey. That meant switching from tree supports to the heavy supports if I wanted to use the automatic support feature in the slicer (using Tango). Also, the model seems to have a little more flex with the water washable. You can see in the picture above, the right-hand side of the railcar wall doesn’t have a flat bottom. It’s curled up on the bottom.

There’s other issues too. I hurried through mesh creation, and left some problem areas (non-manifold edges and faces) that the slicer tried to correct. It left weird slots in the wheels.

Bad printing because of a bad mesh.

Despite errors and problem areas, the chassis painted up well enough to cover up too many mistakes. The middle gap is huge though, and I made it worse by dropping the model while working. One of the deck panels is very loose, since internal supports ran horizontally in the chassis, rather than vertically. That’s because of how the thing was being printed. Supports are made to support the model during printing, not during use. If I want to make it stronger, I’ll need to reinforce the inside of piece (when printing hollow), or I’ll need to suck it up and print a solid block. Neither are appealing. The work to design a honeycomb structure is beyond my skills at the moment, and a big block is heavy and uses a ton of resin.

Primed the undercarriage.

The rest of the prints would turn out okay, and priming and painting with the spray can would make it work as a prototype.

Glued in and ready for priming.
Primed Khador red.
Painting in progress

I’ve had a lot of learning under my belt, and the first change I’m making is to eschew the idea of resin printing an entire engine. These are huge objects, and take a lot of time and materials. Why restrict myself to just one type of material? In the past, I’ve worked with insulation foam and MDF wood products. Part two is going to take you through the rest of the process, improvements and eventually lead to the STL.