Flattening a warp

I broke out an old HO scale resin freight car kit at the end of February and started building it. I think this came into my stash via a trade. The original kits were produced in the late 1980s or early 1990s by the Rensselaer Polytechnic model railroad club. It has become a nice distraction from reality since work began

Before I could start the kit, I had to flatten a few warped castings. I’ve never done this before so here’s the technique I used.

I flattened the roof and two side castings just before having lunch one day. I have a square piece of steel that is about 3/4-inch thick. I put that on my cook top stove and turned the heat on medium. I put a couple drops of water on the slab as a heat warning. If they sizzle, the slab is too hot. A wooden spatula is at-hand in case I need to slide the steel off the heat.

When I thought the slab was hot enough, I placed a warped piece onto it with the flat side on the slab.

A folded over paper towel was placed on the casting to protect the detail as a flat bottom plate goes on top to encourage the flattening.

Once the casting flattens, I moved it off the heated slab onto another folded over paper towel on the counter. The casting is placed with the detail side down. Another flat bottom plate is set on top until the casting has cooled.

When you do this the first time, use a warped part you can build easily. I did the roof casting first as it’s a plain Murphy XLA roof that I have made in styrene. Don’t test the heated slab with a casting that you can’t replicate.

After the casting cooled, I removed flash and squared up the ends. The parts were scrubbed with Barkeepers Friend and set aside to dry.

It was a good lunch.

As many of you may know, the Covid-19 virus has shut down many hobby shows. I’ve been updating the RPM event calendar as information surfaces. A few meets have cancelled, while a couple others are postponed at this time. The Bridgeport meet in Portland, Oregon has rescheduled to an October weekend. I suspect there will be more changes to RPM event calendar in the weeks ahead.

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4 thoughts on “Flattening a warp”

  1. First. Thanks for this. Prior, I had seen where they put it in an oven. That scares me. But your method looks feasible. What about a roof that is not flat? Such as in ECW kits. I have a PRR P70 coach with a warped roof. The walls look similar to what you did and I can try that. But the roof don’t look that easy.

    1. Morgan, IIRC those ECW roofs are injection-molded plastic. I suspect those will deform with a heat application. The parts I flattened in this post are from a resin boxcar kit. I kept the heat at a medium temp for the process. – Eric

  2. Hi Eric,
    For work I used to travel extensively and during the evenings in hotel rooms, I often build models. I had an early F&C covered hopper kit that had warped sides that I straightened out using the bathroom’s heat lamp.

    On another note, do you have any in-service photos of the Central Railroad of New Jersey’s 62000-series of two-bay coal hoppers? They were built in 1913 by Standard Steel Car Co. I have a copy of a builder’s photo, but am looking for something a bit later as I am preparing a kitbashing article on building them from old blue box Athearn twin rib-side hoppers. I’ve built CNJ USRA hoppers and Funaro & Camerlengo’s beautiful 9-panel hoppers that were built in 1919 and am adding the 61000- and 62000-series cars to my fleet.

    1. Alan, thanks for your comment. I’ve had a few flattening castings suggestions and may post a second part with these optional methods. I’ll search my photo archive and check on those CNJ hoppers, too. – Eric

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