Pennsylvania X41B Underframe

 

The (mostly) finished underframe, as described in the following text with photos

In my last post, I discussed my recent clinic for the Philadelphia Chapter of the PRRT&HS. Part of that presentation was about modeling PRR welded box and auto cars and specifically, the work begun on a Sunshine X41B. This post continues that. The focus of this post is the underframe, which is scratchbuilt and relies heavily upon etchings. The images herein provide a mostly step-by-step look at how I replicated the X41B underframe, continuing what had been presented in the clinic. Note that the X41C underframe, shown via photograph in the clinic file, was quite similar, with the difference being that the X41C substituted pressed steel crossties (which can be seen herein and will be noted as such) in place of the two center crossbearers located under the door posts on the X41B, meaning the B had four crossbearers while the C had two.

The image above (all images can be seen in a larger format by clicking on them) was recorded after all the stringers between the bolsters and the four main pairs crossbearers were added. The flanges of the center sills, 0.010" x 0.060" strip styrene were also attached, completing the center sill sections between the bolsters. Note that the crossbearer sections that are located where there are separate side sill support tabs extend past the edge of the floor. This is because these will tie directly into the channel shape of the etched tab sections.

These two images provide other views at the same stage as the photo referenced previously. One interesting (and cool to this freight car geek) thing is the difference in "height" of the stringers between the crossbearers (five scale inches) versus the stringers between the crossbearers and bolsters (three scale inches.) The difference is quite pronounced and shown to good advantage in the photo below. Note that the floor had not been glued into the body (yet!) at the time of these photos.

The floor had a slight bow to it from end to end. In addition, it was necessary to tack the floor into the body, yet leave the areas away from the center of the car "free" in order to ensure proper orientation of the crossbearers and their corresponding side sill support tabs. I carefully secured the center portion of the floor into the carbody with ACC, in the area highlighted in the graphic shown above. This served to secure the floor into the body, yet allowed some "play" to adjust the alignment of the floor relative to the carbody when securing the outer crossbearers and their tab segments.

The preceding three images illustrate how the crossbearers and the tab side sill support sections are integrated and attached. The beauty of the etchings is that they are thin enough in profile to accurately mimic the prototype and yet are still quite durable. Again, note that the ends of these crossbearers extend past the bottom of the side to nest into the channel of the tab.

The crossties were created by drawing the basic shapes with fold lines in the appropriate spots for etching. These came out exactly as planned, nesting into the center sill flanges and clearing the stringers. The ones between the side sill support section in the center of the car required some shortening to fit. The ones at the tab sections nest into the channel "behind" the tab sections. The photos above and below illustrate the crossties.

The side sill support tabs that have been replaced with etched parts are visible in this side view of the model

The lower bolster cover plates feature "knockouts" in the exact shape of the prototype. They were bent slightly to match the shape of the scratchbuilt bolsters.

The image above shows the underframe after the addition of the bottom bolster cover plates, as highlighted in the previous photo

The two preceding photos highlight the addition of the bottom crossbearer cover plates. While I etched pieces for the segments that span the center sills, I opted to use 0.005" styrene as I found it generally easier to work with and the shape is a rectangle, as opposed to the complex shape of the outer portions of these unusual plates, where etching made the work of matching the shape far easier.

The channel section crossties had a small rectangular steel brace that was welded to the crossties and the center sill. This is simulated with an etched piece, as illustrated in the two photos above.

The stringers between the bolsters and end sills incorporated trapezoidal-shaped plate that was welded to the ends of the stringer and to the end sills, tightening things up a little more. These are simulated with etchings, as shown in the two accompanying photos.

While there are still a couple of things before the underframe is completed, including truck mounting and simulated bolt heads on the stringers, as well as the brake equipment, the basic structure is complete. The next post will pick up to cover brake equipment and other details. Stay tuned...