Shell & Mech Frame

A closer look at how the shell sits on the mechanism frame. There is a shelf at either end of the mechanism that extends out a bit. Here I have the top labeled. This is a ‘starting point’ .. the important thing at the moment will be the bottom of this shelf.

Mech Frame Thickness

With the shell removed we can see the shelf much easier. If I remember correctly the tabs snap into pockets on the inside of the HO shell to help lock it in place. The .060″ / 1.52mm thickness here locates what will be the bottom of the locomotives frame – or more precisely .. what will LOOK like the bottom of the frame. From photos it seems that the locomotive frames are approximately 8″ thick. What this means is that I will ‘wrap’ the shell over this shelf down to the bottom of the shelf – and then thicken this to a scale 8″ thick. In O scale 0.166″ / 4.233mm.


Working up steps and stuff. Trying different versions etc. Need a set of steps from the door level to the level on the nose. The blue is from the GP9 set .. the doors below the cab. The orange color is the frame. The cab position depends on how the steps turn out.

Orthographic Projection

Here’s a quick .. very quick .. look at the locomotive. It is just a bit over 19′-3″ long, 12’2″ high and 9′-10″ width.


Here’s a quick overview of the exploded engine –

  • The part in white and orange is one part. The orange is the frame – I think I will visually separate the frame and the white part with a’engraved’ line. I will probably extend the ‘frame’ all the way to the end/coupler pocket. That will require reworking the steps.
  • Steps in red. I test printed one step – it might be better to print them at Shapeways .. but that is way way down the road as yet.
  • The blue parts as shown are from a Red Caboose GP-9 detail parts. I don’t know what they are called .. they are battery boxes and other ‘things’ with doors. That explains the white part that sticks up .. the blue parts glue to them.
  • Purple – that is an Atlas O Scale cab.
  • Green are the short and long hoods.

The cab (purple) obviously is ‘what you get’ – things like modifying is up to the modeler – but the starting point is pretty much ‘set in stone’. The blue parts again can be modified easier since they are flat plastic and could be cut as needed. This would mean the white parts they glue to can be shortened as needed. Steps of course are modified to fit. The hoots (green) again, can be modified as needed. The ones pictured are just a quick and dirty example.

I wanted to preface what follows with this overview. One of the problems I have run into with 3D CAD design is when someone starts with “Can you make THAT thinner?” .. “Can you ‘make that narrower?’ .. and a string of other such similar statements. The answer is often ‘it depends’.


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