EMD F7 in SCALE
BODY CONSTRUCTION: Part V
One of the most complicated aspects of building the body was fabricating the main (center) roof hatch assembly. A number of pieces are part of the assembly, including the hatch itself, fan deck, exhaust stacks, reinforcing ribs, fan adapters and fan grilles. Excepting the grills, all parts are fabricated from sheet steel.
Above is the main hatch sheet after rolling. The fan deck fits into the rectangular opening, as well be seen in a later picture.
Above is the fan deck with one of the supporting ribs jigged in place. These ribs extend under the main hatch sheet to tie the structure together. The ribs are a bit of overkill in material thickness to help prevent distortion during welding.
Above is the fan deck after the supporting ribs and exhaust stacks had been attached. A lot of care was taken to get things as accurately positioned as possible, since the main hatch is a point of detail that is immediately visible to the casual observer upon seeing the locomotive for the first time.
Once I had finished the fan deck it quickly became apparent that a simple fixture would be a big help in getting everything lined up for welding. So I got busy.
This fixture was fabricated from a piece of extruded aluminum tooling plate drop that I picked up from a local machine shop. It was a bit too long, but I was able to put this piece into my (9" × 13") horizontal band saw and shorten it to the required dimension. I fabricated some clamping bars out of 1/2 inch thick cold rolled I had laying around. The two large holes bored through the plate give clearance for the exhaust stacks when the fan deck assembly is in place. The clamping bars then secure the deck, with bolts threading into four tapped holes in the fixcture.
Above is what the hatch assembly looked like after jigging. The cutout in the center of the hatch naturally pilots on the deck's perimeter, which made achieving alignment fairly easy. A long piece of rectangular tubing acts as a clamping bar to hold the entire mess in alignment, along with the usual army of C-clamps.
As all of the sheet metal pieces are 16 gauge, I used 0.025 inch wire in my MIG welder, along with 75/25 shielding gas, and skip welded the joint between the deck and the hatch sheet, as cosmetics would be important. Somewhat heavier welds were made to attach the ribs to the hatch sheet. These welds produce some localized distortion that would be visible on the exposed side of the hatch, which is not necessarily a bad thing—such distortion can be seen on the hatches of the real F-units.
The next post will have some pictures of the completed weldment.