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AC Units The MBX building is large. With two-thirds of a 350,00 square foot building air conditioned, there were many AC units on the roof. I could not find any Z scale ac units to purchase so I bought an N scale ac unit to get some ideas. I determined I could build them myself but there would be too many to build. I decided to make a master and use a latex mold. The stuff I got a number of months ago had gone bad and took my original master with it. The first master wasn't very good anyway. I found out that molds would only last for about ten or fifteen molds and then you needed to make a new mold. I decided to make four masters and I use some brass sprue to make the ac doors and some N scale brass Venetian blinds for the grills at each end. I also used some small diameter styrene rod for the vent stack on top. The body was made up of misc strip styrene.
After the four masters were made I glued them to a styrene base and then built up walls to create cavity for the mold material. The mold was very easy to use and I let it set up over night even though it was advertised as a 4-hour curing time. It is sort of pretty; one part is white and the other is blue and when mixed it turns out beautiful blue. The castings were made from clear polyester casting resin. This stuff was messy to work with and smelled awful. But once done the castings turned out ok. I airbrushed them first with light gray then silver then gray again to get a combined silver-gray look. I made two four master molds and poured five castings for a total of forty units. One mold held up fine and I can use it again if needed. The mold, while still usable, is show a few tear marks around the corners of the masters. It should be noted that the mold turned out very good because of the extra thickness all around the masters. Were that thickness not there, the mold would not remain true to the master and the castings would not be any good. Materials: Assorted styrene Brass sprue Brass Venetian Blinds Castin' Craft Clear Polyester Casting Resin (two part) Micro-Mark One-to-One Silicone Mold Rubber Polly Scale Undercoat Lt Gray paint Polly Scale ATSF Silver paint
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