D&RG #168 - Engine Parts Integration

Now that the workshop is back in order, I'm getting through some print-fit cycles for the engine:



Cab and boiler are pretty well done, front end is where I'm currently working through issues. Note the pilot footboards; I integrated them to print with the front end, but their mounting strap is just too small. It's sized correctly prototypically, one of those cases where it will get a little "beef" for model integrity. There are four uncouplng levers arranged across the pilot beam top; well there's two now, I scraped the nearest two off assembling the front-end to the frame.

I changed the frame design to use a brass spine from cylinder chest to the cab, you can see a bit of it just rear of the chest. A fully resin-printed frame just wasn't straight, made the front-end droop.

Note the handrail stanchions, printed integrated into the boiler assembly. Just a thou or so larger than correct, made a world of difference for their survivability. Handrails themselves are 24 gauge piano wire. I'm going to use various gauges of wire for piping and such, looks a lot better than trying to print them.

I printed drivers for the static model, they came out quite nice. I've got side and connecting rods printed, such delicate things, they'll just get glued on for the static model.

I've got the tender CAD-ed, except for some of the details, but I'm deferring printing any of that until I get the engine worked out. Indeed, I'm learning a lot there that'll make the tender integration a lot easier...

 

That looks great, you've come a long ways

Sumner

 

I've found that the part-by-part modeling of such a locomotive's parts to be pretty straightforward. The real challenge has been in the integration of parts, and the organization of the project. The latter is just probably due to my use of OpenSCAD; I'm sure a more capable program like OnShape or Fusion360 has tools like projects and assemblies to help. But integrating a scale model has been a series of iterations, some involving complete redesign of certain parts. Also, finding out the limitations of the medium has been interesting; even with the static model I'm finding there's still utility in using metal for certain things - as of now, brass for the frame spine and wire for piping.

There are also scaling things to keep in mind, the small size of HO scale requires modeling license to mitigate limitations of the medium and the tools. I pointed out the need for a beefier footplate support; another are the dimples in the footboards. Right now, they're 10-sided spheres, finer-detailed ones just bogged the OpenSCAD renderer. Works for HO scale where each is only a few pixels of material, but that won't look nice if scaled to O or maybe even S.

Photographs have been essential to this iterative process. Right now, i'm looking at the above photograph and noticing the waviness in the boiler footboards. Probably needs a thou or two more of thickness, methinks, which will change the placement of the dimples, and so on...