A little work straightening a casting

Attempt 1 - unsuccessful!

I have been slightly grounded of late after two surgeries to repair a torn retina, plus a mild heart attack this week for my ex-mother-in-law (who’s doing very well) and lengthy dental and orthodontic appointments for my son. Some of these things have just consumed time, but the retina “thing” has affected my ability to do some of my work and my ex’s mother does a lot of the heavy lifting of getting the kids where they need to be during the week. The eye situation is kind of tough when most of what you do centers around discerning details and either writing about them or recreating them in scale!

One thing I did was to pull out a Sunshine Models PRR F30A kit to scan the side to use as part of the process of creating decal artwork. I had to clean up the main car casting (literally a casting as the prototype used a cast steel underframe with integral stake pockets and other details!) In doing so, I noticed that the portions of the car between the ends and bolsters had a noticeable droop. I did what I usually do and put the casting on a piece of glass and put it into an oven that had been preheated to 250 degrees and turned off prior to putting the glass and casting into the oven. The casting softened, as they usually do. I put the “weights” shown in the photo on the casting until it cooled* (the graphic at the bottom of the page illustrates the relative structural strength of shapes and displays while deep side sills and center sills are great at provide support to the car body or loads.) All great!

Well, when the casting cooled, I noticed that the opposite of my goal had occurred. While the ends were now flat, the center of the casting had developed a noticeable droop, making the car look sway-backed. Normally, a flat car model would have solid center sills to straighten things or I could insert a piece of square steel or brass to get things straight. However, this car is an unusual prototype and the center sills are segmented, as opposed to being two single longitudinal pieces between the bolsters, and not as solid as the side sills, meaning that depending upon them to aid in straightening the car body was an uncertain proposition. 

I reheated the casting and while it was still “soft” I used my drill bit box and one of my “weights” to try to remove the sway-back curve. I tried this several times to no avail. The casting seemed to have memory of the swayback shape. 

Attempt 2 - unsuccessful!

I resorted to something that engendered greater risk, but given that the heating and flattening method was not working, was a risk worth taking and if it failed, I could always perform the heat and flatten method to return to the previous shape. I held the center of the casting under extremely hot tap water and after I knew that the casting had become slightly pliable, I applied force with both hands to bend the casting to straighten the center portion. I then changed the water to simple cold tap water and held the casting under until it hardened. The method finally yielded the results I was seeking…. or mostly. There is still a trace of a bow on one side, but it is hardly noticeable and I am hopeful that when the deck is glued in place it will provide enough stability to pull things even more into shape.

As always, your mileage may vary.

I will be doing a full writeup on this car, although where I will post it and how is TBD.

Happy Holidays

*no, the weights do not deform the casting. If you put weight on to a relatively structurally solid piece of a casting, it shouldn’t sink or deform from the weight. Now I’m sure if you heat the casting excessively and use a lot of weight, I would be proven wrong, but I try to get things soft enough and only use enough weight to apply the proper pressure. Also, see the graphic to understand a simple property of structural integrity.

Relative structural strength