FP7 Steam Generator Housing
Article reposted by the generous authorization of Pat Durand's son Casey.
The Alaska Railroad's three FP7 locomotives, 1510, 1512 and 1514 were fitted at the factory with a unique stack assembly over the steam generator. I believe these were a cold weather adaptation that may appear on some NP, GN and Canadian FP units as well. I have not found any drawings of the housing. With all three locomotives gone, we modelers were left with lousy photographs from which to imagineer these devices.
I built several housings one at a time, and when folks started asking me to build them, I created a simple pattern in styrene, to include the drill pilot dimples and added some bolt head detail. This was fixed to an extra highliners hatch cover to form the proper roof curvature.
Next step was to build a mold box of styrene around the pattern and fill it with Bragdon two part silicon mold material. The resulting mold was then parted and sprayed with cheap auto gray primer as a parting agent. Then a small amount of two part casting resin is poured into the mold and prodded with a straight pin to remove bubbles. Capillary action actually pulls the material up to the edge of the mold to form the curve.
After 20 minutes the housing is removed from the mold and the primer color used for a parting agent has been integrated into the part. Then it is drilled to accept two pieces of tubing for the intake and exhaust stack and two pieces of wire simulating the piped extensions of the safety valves. The raw assembly is at the right in the photo. A little filing and it is ready to mount with the large exhaust stack centered over the original stack position on the model.
Simple forms are easily duplicated with this casting process. This is not a production mold but the resulting part is very presentable with a little work and paint.
[Editors note] Orginally posted on https://alaskarails.org/ARR-modeling.html