Bowed urethane castings - thoughts on a fix?

[DaveJfr0]

Here’s a fun one.

Was looking to finish up a car of mine that has been painted for years now to find that the body casting warpage has only gotten worse where the ends are bowed downwards.

Anyone seen this with urethane castings? This is one from Wiseman models. I emailed him about it but wanted to see what the Oracle of MTJ thought.

I’m not sure if this bowing is intrinsic to the urethane formula used or not. It’s never been in sunlight or anything more than room temperature.

Was thinking of trying to throw my heat gun on it and bend it back straight or sandwich it between two surfaces to straighten it where I want it and then apply heat. Just afraid to damage the detail parts on it that are not urethane. Not sure if it’s a lost cause, but I hope I can rescue it.

Pictures of the madness:

[Rufus T. Firefly]

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[DaveJfr0]

The base car is this: https://wisemanmodelservices.com/O-SCAL ... ONDOLA-KIT

They were also repurposed for transfer cabooses later in life which is what I was going for. Its mostly finished except for some brake wheels and handrail details. I'll get two photos on here later when I can to show the extent of the bowing where the center is higher than both ends.

[Rufus T. Firefly]

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[sarge]

Sounds like the material is unstable and the sills and main frame member are shrinking.

Unless he has a recommendation on relaxing the casting permanently, you might be best served by milling the centre frame member out to make the thing flexible enough that a brass "I", two "els" soldered back to back to make a "T", or rectangular tube can be run up the centre underneath. Then, a series of countersunk flatheads through the casting from the top and tapped into the brass to pull it straight(er). You then can cover the heads with the decking.

[ScaleCraft]

yeah. boy.

https://wisemanmodelservices.com/image/ ... 00x900.jpg

Not like you can do that without a bunch of cutting.
You'd have to do all three major components, center sill and side sills.

Too bad it's all painted. Still, I think I'd try heat.

[ScaleCraft]

http://modelrailroadersnotebook.blogspo ... odels.html

https://cs.trains.com/mrr/f/88/t/260266.aspx

I asked this question to Claire Gilbert.I had purchased one of his building that was warped He advised to take a flat baking sheet and put it in a low oven. (200-250) to alow the resin to relax. Watch closely and remove to cool once the part had straightened itself. He also advised using an old toaster to avoid upsetting the family

I finally used wy wife's hair blower on high heat. I placed the parts on a piece of glass and exposed them to heat for a few moments, seconds not minutes. Every part straightened itself pretty easily, even the thickest one.
====================================================================================================

Heat. Not a lot, but consistent.

[DaveJfr0]

Added two photos. Can take more.

Its not my camera, the body is really warped that bad.

There is a piece of metal weight in the center hidden in the sill that is probably the only thing from keeping it from being worse than you see.

I'd be afraid to put the casting into the oven without removing the detail parts on the underframe as well as the metal weight. I'm thinking that maybe a heat gun is too much and a hair dryer would be better, but Sarge is right and that I'd want to make sure whatever the fix is, its permanent. If I warm it up and its good only for 6 months before it needs another heat treatment, that's not great.

May be time I go look for some of these that came from SMMW rather than the recasts from Wiseman. I should at least be able to salvage some portions from the original body and I think I have spare decals for sill. Just a PITA if I have to redo my work.

[DaveJfr0]

I forgot I built this, but it has the exact same warpage curvature. Can't remember if its the SMMW casting or not. I believe it is actually SMMW. Maybe its something to do with that metal weight in the sill. The wood decking has started to come up. Fun.

le sigh. I guess I have nothing to lose with some heat. Guess I'll turn it upside down and try my best to heat it up and straighten it. May ruin some stirrups in the process. They don't like heat, but salvaging the cars is more important.

[ScaleCraft]

I dunno. Everything I have read on this indicates heat removes the stress, and nobody says it comes back.

You may wanna try one to see.

200 on a cookie sheet shouldn't hurt details unless they're plastic.

Now, with doorstops, you get warping like that, you pull all the bits (trucks, couplers, steps, grabs...) and throw it away because it would be Zamac Rot.

[bob turner]

Not entirely true - I have a Lionel caboose (looks like a 717). The floor was seriously warped, so I clamped it with some force, put it in the oven, then once heated pulled it out and re-clamped until straight. That was almost 60 years ago - still straight.

I know nothing about urethane, but suspect Dave is correct - relieve the stress, and it stays relieved. But imbedded metal is a problem with plastics. Note the Weaver gear problem - they forgot to age their nylon gears, and they all split from shrinkage.

I shall stick with wood and metal - which is my loss, since plastics and urethanes are now producing the best detailed models.

[ScaleCraft]

Note the Weaver gear problem - they forgot to age their nylon gears, and they all split from shrinkage.

I knew a guy in Brookings, Oregon who worked in toys/hobbies/whatever, HE said nylon gears are great IF you treat them.

He would get a new loco, pull the gears (or drive axle with gear) and boil them in a pot. Don't remember how long, but let them cool, re-install and lube, and they never go bad.

His last comment was the PRC is too cheap to spend the time to do that.

[DaveJfr0]

So I experimented with the flatcar upside down. I clamped down both ends and applied high heat with an hairdryer. Not much straightening occurred.

I then took my heat gun and put water-soaked paper towel over the plastic details (as one of the stirrups and clevis began to buckle without them) and focused mainly on the ends as well as the center sill, hoping it would heat up and relax in a straightened position. That lovely smell these kits give off in the mailbox came back briefly.

As it cooled, I could hear several cracking noises, and while the car didn't fall part, when I removed the clamps, its bowed worse. lol. Maybe I need to apply heat on both sides? I'm working on getting off the wood decking, so I can look at possibly removing the metal weight inside.

I'm tempted to try the oven at 200 and just replace all the plastic parts that are surely going to melt. It's also possible this urethane material won't ever relax. I also never heard back from Keith Wiseman. What a PITA these cars have become.

[robert.]

Boil it. That will give you equal heat all around. without such nasty direct heat causing it to melt or burn. Place a tee shirt in the bottom of your pot. This will keep the car from banging around with raising bubbles.

[DaveJfr0]

Boil it. That will give you equal heat all around. without such nasty direct heat causing it to melt or burn. Place a tee shirt in the bottom of your pot. This will keep the car from banging around with raising bubbles.

Wouldn't that still melt the plastic or styrene bits? How would I force it to straighten, or are we all assuming it'll just straighten on its own if heat was applied equally everywhere?