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About this Model

Detailed Description:

This is a model of a railroad caboose which I copied from my N-scale model railroading stock. The model is a complete solid geometric model which can actually be manufactured.

The main and top walls were created by subtracting one box primitive from another. For the windows and doors, a prototype was built and then transformed to each location on the walls. The external window frame was added to the wall, the internal frame was then subtracted (for the walls on the lower portion of the caboose), and finally the window itself was subtracted. After the roof was built, it was subtracted from the walls so that the roof would fit nicely on top of the walls. The upper walls were subtracted from the lower roof so the top section is accessible from the lower section.

The base was created from a box primitive with numerous components added. The ladder and rails were added using a boolean union operation. The ribs and wheel shafts were added in a similar fashion. For the stairs, a profile box was subtracted from the base to make space for each set of steps. Then the steps were added with a boolean union operation.

The wheel truss was the most difficult section of the model to build. The side truss was created by extruding a profile curve for the top and joining it with an extruded profile curve for the bottom. Wheel hubs were then added and holes for the axle subtracted. The bottom truss was also created from an extruded profile curve. In addition, a two pocket pattern feature was subtracted from the sides of the bottom truss and a hole was subtracted from the middle so the wheel truss could rotate around a shaft for steering. The springs were built from a tubular surface along a helix curve. The difficulty with the wheel truss was subtracting the overlapping portions of each of the above parts so that they could be assembled into a complete wheel truss.

The wheels and axle are the simplest component in the model. Each wheel and axle set is a surface of revolution created from a profile curve.

Specific Features or Unique Modeling Approach:

Adding the windows and doors to the walls of the caboose was greatly simplified through the use of anchors. An anchor was defined pointing out from the top left corner of the window prototype. For each instantiation of the window, an anchor was created at the proper location pointing out of the caboose. The prototype window anchor was then transformed so that it matched the anchor on the wall. The windows were then created as discussed above.

Variable were used to specify many of the dimensions of the model. This facilitated matching the various components so that they would fit together. It also simplified changing the dimensions when something was not in the proper proportion.

Difficulties:

Boolean set operations to combine the various surfaces caused tremendous difficulties. Success of these operations was very sensitive to the order in which they were performed and the location of the surfaces being operated on. Much of this was due to the inability of the combineShells boolean set operator to handle any coincidental surfaces, edges, or vertices.

Source File(s):

caboose.scl
wheeltruss.scl
wheels.scl
ladder.scl
rail-stairs.scl
doors-windows.scl

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