PRR GLa - Construction: Exterior
12/12/2015
I spent some time thinking about how I was going to tackle the ribs. Nothing came to mind, so I decided to make them in a similar fashion to the way I had done them on the PRR H21a hopper I built several years ago. As shown in this rather dark photo, I started off by marking the centerline of the ribs' positions on the top edge of the hopper body, so that I could glue a scale 2"x4" piece of styrene on its 2" edge. I used a small machinist's square to line up the styrene strip, quickly applied the glue using a small paint brush, and immediately pulled the square away from the strip (to keep the strip from sticking to the square). The back two ribs show that state. I then glued two 1"x2" strips along either edge, with their 2" surface glued to the body (as shown at the other three ribs in the photo).
Construction: Exterior
When the styrene had had plenty of time to dry, I carefully cut away the top and bottom excesses. The top is rather easy to do with a small file. The bottom excesses had to be carved away with an Xacto knife. The lesson I learned very quickly was that I should have done the exterior ribs first, and then used them to help me to correctly position the interior crossbearers. This was because somewhere along the way I didn't get them marked up and positioned correctly. It is painfully obvious when you look at the model with the light coming from behind. I decided to let it go on these first ones, but I will do a better job the next set I build.
Construction: Exterior
This portion of a prototype photo clearly shows the shaping of the ribs. The top angle starts at about where the top of the side panel reaches the corner post. The bottom angle starts at about where the side sill of the frame starts.
Construction: Exterior
Shaping these ribs involves a number of steps, but none are too difficult. First, I sanded the ribs to where they are about 3-1/2" tall. Next, I marked a line on top of the ribs matching the spots at which they are to start to angle, using a ruler across the whole side of the car. I gently sanded the angles using the stand shown in the photo. The sandpaper block is made out of two pieces of MDF, to which the sandpaper is glued. This is the hand plane I use to sand the tops of the ties even when I handlay track. The stand allows me to focus my effort with my other hand in carefully directing the car's side evenly across the sandpaper. I just kept sanding it until it met the angle of the prototype photo, up to the lines I had marked on the tops of the ribs.
Construction: Exterior
If you look at the ribs of the prototype, they are rounded. I tried to simulate that by, in a carving style, sliding the Xacto knife (I later switched to using a razor blade), at about a 70-degree angle - almost perpendicular, across the sharp edges of the ribs. Eventually they wind up with a bullnose top. It takes a bit of time and some patience, but it is not hard to do. The first rib on the left in the photo looks curved, but that is a photographic distortion, because it was almost touching the camera's lens; it was that close.
Construction: Exterior
Here's another close-up view of the ribs. The three on the left are done, while the two on the right are not. The two on the right have had their rough shaping done. Anyway, the ribs on the three cars under construction are now all done. As a note to myself for the future, install the ribs first, then install the crossbearers, and then come back to shape the ribs. The installation of the ribs ensures that the crossbearers will be in the correct position, while the crossbearers are necessary to hold the side panels firm to be able to do the shaping of the ribs.
Construction: Exterior
The next step is the chord at the top of the car. This provides structural integrity to the tops of the side and end panels. Since my model is made out of styrene, it is very light, so I started putting these metal weights in the car so that it is easier to work with it. I decided to make the chords using scale 1"x6" strip styrene.
Construction: Exterior
I cut the ends at a nice 45-degree angle. The chord strips are flush with the inside of the car's panels.
Construction: Exterior
Part of the delay of posting an update on this project is that I struggled with how to correctly model the corners of the chords. If you look at the prototype photo back up this page, you will note that there is a piece of metal placed over the corner. It seems like it is hand-formed to curve around the corner, and there is a bit of an edge folded down; almost like a drip-edge. I tried forming that using a butane torch, but that melted the styrene test piece too quickly. Next, I tried forming it by hand using a strip of brass sheet. However, that just didn't come out right (I probably don't have the correct tools for doing that kind of work anyway). Finally, I tried heating a piece of styrene again using a hot-air gun. That worked reasonably well (i.e. I had more control over it), but the end result still wasn't anything that looked like what you see in the prototype photo. So, in the end I punted and just glued on a scale 1'x1' thin piece of styrene, slightly offset from the outside edge of the chord.
Construction: Exterior
I then used a razor blade and cut away the inside corners.
Construction: Exterior
The outside corner I filed down to give it a curve, somewhat like the prototype. I am relying on the shadow to create the effect of the "drip edge".
Construction: Exterior
I used an Exacto knife to scrape away any glue and misalignment between the chord and the inside edge of the hopper's sides, and the photo below shows the current state of the three cars.
Construction: Exterior
There is a sheet of metal that supports the angled slope of the hopper box and rests on the truck bolsters. I started off by cutting a piece of 0.015"-thick sheet of styrene to 9'4" wide by 2'6" tall. I then custom-fitted it to the interior space of that opening, as best I could.
Construction: Exterior
After many tries, I eventually got it to fit. A bit of glue holds it in place.
Construction: Exterior
In the prototype photos it shows a strip of metal across the seams. I used two strips of scale 1"x3" styrene and glued them in the intersection between the vertical sheet and the slope of the hopper.
Construction: Exterior
Similarly, two strips of styrene were added at the bottom of that sheet. This also nicely hides any gaps.
Construction: Exterior
There are two diagonal braces running from the outside to the center sill. Later hoppers had these going in the opposite direction, but the GLa had them in this direction. I cut them from scale 8" wide styrene C-channels. I filed one corner into two 45-degree ends, and then filed the opposite corner to custom-fit. The yellow clamp was used to hold one end of the strip up while I applied glue to the other corner. By the way, while I was working on these, I realized there was quite a large cavity available behind the vertical wall sheet that I glued in place above. So, that area, too, was filled with lead shot. I also reviewed the other areas to make sure they were all as full as they could be with lead shot, without being visible from the side. This made the models nice and heavy, even without a load.
Construction: Exterior
There are triangularly-shaped gusset plates on top of those C-channels in the prototype photos, so I cut some 1'x1' squares out of 0.010" styrene, and then chopped off one corner using a razor blade.
Construction: Exterior
I was then able to carefully place them on top of the C-channel and the side sill, and touch the glue-saturated brush to them. This completes the diagonal braces.
Construction: Exterior