Rails Unlimited Urethane CB&Q SM-16 Stock Cars

Great work Sarah!! Looking forward to your completion. Have you called Ted?

Sarah, looking good so far. Sometimes working with kits that are warped can be frustrating. The key word is patience............Paul

I have no experience with these kits, but some with resin and plastic kits in general.  Most likely the boiling water is not getting the parts hot enough to relieve the internal stress which caused the warping.  Maybe try in a steam basket.  If that doesn't work try the oven:

My friend God rest his soul Chip Rovetta commissioned this project with Ted. Yoder trucks or American Scale Models trucks work nicely on them. 

My friend Jefferson on here has worked to this master of a Rock Island stock car and I believe they were finally offered for sale 

From my experience, warped castings in flat unbuilt resin kits come from a number of different circumstances. Removing the casting from being captive in the rubber mold weighted down with a flat plate on the open side before they cure totally rigid can allow some warpage to occur, even when placed on a flat surface to cure.  The resin doesn't really fully cure a lot of times for up to a week, depending on the resin, humidity, accuracy of mixing the two components before pouring, etc. Some tooling resins shrink a lot.  Other urethane consumer type resins also shrink more than others, usually the faster the cure time the more shrinkage the casting will see. This is thousanths of an inch per inch of length, which in HO scale is not too serious but because O scale castings have far more mass and are usually much longer, it can become a real issue.  Castings that are open poured which are not then covered and weighted down to cure will almost always eventually bow in both directions over time, I don't know why that matters but it seems to. All resins shrink to some extent, but the ones with high shrink rates will also noticably shrink on the side of the casting that has the most detail in all directions to the point that it pulls the casting bow shaped in both directions from the other side. These are virtually impossible to fix and use to build a model with. It's a good idea to drill a really small hole in the middle of the bottom of the floor of your model, since even after building it up into a box, the castings will degass to some extent for a long time, especially if they get warmer, and if there is no place for the gas to escape, the thinnest castings in the car will begin to bow outward from the pressure and be ruined(obviously not an issue with a stock car). The WORST thing you can do with a built up resin car or kit is to place it in direct sunlight, or leave it in a hot car interior.  ABS plastic will tolerate this pretty well but not cast resin.

That said, the resin the CB&Q stock cars were cast with seems pretty soft in its finished state. I just left mine on a flat surface for a month or so and they went back flat.

Oh, I should add to this, as soon as you purchase a flat resin kit, you should take the parts and lay them on their flat side on something flat. Leaving them for long periods of time jumbled up in the box or worse, being pushed on by other parts in the box, can and will lead to warped castings when you go to use them down the road. Or you could cut some flat plywood or plexiglass and rubber band them to it and put them back in their box standing upright(on edge), this will keep them pretty straight.

TexasSP posted:

I have no experience with these kits, but some with resin and plastic kits in general.  Most likely the boiling water is not getting the parts hot enough to relieve the internal stress which caused the warping.  Maybe try in a steam basket.  If that doesn't work try the oven:

Steam is certainly hotter than boiling water, might work.  I'd be REAL leery about using an oven.  One of the two sides of urethane resin is pretty nasty stuff, especially if inhaled. I'd be afraid of the fumes that an oven might produce when heating urethane castings. The cured product is pretty safe, with the dust you get from it by sanding or whatever not really dangerous. If the sanding process produces enough heat to make it smoke though, breathing that might not be.

I also have some epoxy resin cars of old, and a couple of them seem to be "leaking" a brownish colored liquid in a couple places. From what I understand, this is the resin portion of the two part mixture that was not mixed with the activator well enough when cast and is "venting".  Glad they are not painted yet. I plan to clean it off with solvent and then spray the car with sealer before painting in the hopes it will block it. Maybe it will leak into the interior of the car then, I don't know.

All this talk about fixing stock car kits has made me consider becoming a vegetarian! LOL

Clever clamping, Sarah.  You are on your way to becoming a Master Craftswoman.  No joke here.

Ed

Thank you for all the comments! Now I'll go downstairs and make sure to re-pack other kits. Thanks TEXASSP, that's a good point! I'll try different kinds of heat to some parts that I don't include in the kit. Very nice models, Erik! So after six of these you really know how it's done :-)

O.K. Here comes question two: How do you prepare the material for painting? Is a brush wash with soapy water sufficient? Do you recommend a certain primer?

Thanks in advance!

Sarah posted:

Thank you for all the comments! Now I'll go downstairs and make sure to re-pack other kits. Thanks TEXASSP, that's a good point! I'll try different kinds of heat to some parts that I don't include in the kit. Very nice models, Erik! So after six of these you really know how it's done :-)

O.K. Here comes question two: How do you prepare the material for painting? Is a brush wash with soapy water sufficient? Do you recommend a certain primer?

Thanks in advance!

That's a tricky question.  It depends on what, if any, mold release the caster used when he made the parts. If no mold release was used, then the parts will have silicone on them that wicked out of the RTV mold and will fisheye when painted. If the caster used an mek based primer on them(like the early Raills Unlimited car bodies) they are preprimed and ready to paint. If the caster used most any other mold release, some of it will be left on the castings and may or may not cause an issue. You can use different sorts of cleaners on them, 409, Fantastic, etc. Some people have used oven cleaners. Washing with dish washing soap is probably what most people do unless they just prime and paint them and hope for the best.

My stock car showed a little fish eye when I painted the insides, so I will spray some 409 on them, rub a toothbrush on them(not my current one though) and rinse them off and let them dry before doing the car itself.

If you intend to spray primer on them for a first coat, which is probably a good idea since the car will be part resin, part plastic, part brass details probably, then any good name brand model primer will work and not hide detail. Model Master Fine primer is nice, but laquer based so be careful on ABS plastic. Tamiya makes an excellent rattle can gray primer as does Testors. These are all made for the scale plastic model crowd and are really fine particle paints.

Sarah posted:

O.K. Here comes question two: How do you prepare the material for painting? Is a brush wash with soapy water sufficient? Do you recommend a certain primer?

Thanks in advance!

Depends on the resin and who did the casting. If they used a mold release, possibly silicone in nature, most recommend in their instructions the warm soapy water and scrub brush step, although that really should not impact a silicone based agent.  Mineral spirits would be more effective.

This is why I rarely bother to use a mold release agent......

Primer - 2 schools of thought - 1 - use a basic primer of general grey color so it's easier to paint over or -2- just put a first coat of whatever color you plan on using and call that the primer

Nice! Looks like a great kit to build:

I've had good luck flattening castings of R.U. kits by placing them on plate glass, weighing the end edges, and placing an incandescent reflector lamp (60-75w) about 6" above.

I leave it overnight to warm it through. Then let it cool while still weighted. Works for me.

I would be leery of the oven as I had a baking oven made for drying paint on models and even with the oven cracked partly open it warped the heck out of a resin passenger cars.  I would try the weight method and perhaps adding some heat to speed the process.  Perhaps a heat lamp focused on it or a heating pad under or on top allowing the heat to soak thru while the weights do there work.

oscaletrains posted:

.................................. rub a toothbrush on them(not my current one though)...................................

Good thinking.

Either that, or sometimes I use my wife's toothbrush (her current one) for a few of my model brushing needs........ 

Mixed Freight posted:

oscaletrains posted:

.................................. rub a toothbrush on them(not my current one though)...................................

Good thinking.

Either that, or sometimes I use my wife's toothbrush (her current one) for a few of my model brushing needs........ 

That'd get you sleeping in the garage or something.

VGN64 posted:

I would be leery of the oven as I had a baking oven made for drying paint on models and even with the oven cracked partly open it warped the heck out of a resin passenger cars.  I would try the weight method and perhaps adding some heat to speed the process.  Perhaps a heat lamp focused on it or a heating pad under or on top allowing the heat to soak thru while the weights do there work.

 

We have all either seen the results or heard the stories of those unfortunate modelers that baked the paint on their models so well that the solder melted and the model turned into a pile of parts.  I've baked my share of Scalecoat paint on models and never had that happen, though I never let the heat go over 200 degrees.  For resin it'd have to be a very precisely controlled oven. But some people who cast resin do indeed use an oven to cure the castings faster. I have no idea the temperatures to use for that but I imagine it is pretty low.

I don`t recommend an oven for flattening resin parts. Too hard to control the temp and disaster is a possibility. I have had good luck with a heat gun set on low and a few weights. Of course you have to be paying attention and start with light passes. Especially with thin stock car sides. I use a right angle piece of stock brass glued inside along the top of the car side to straighten and strengthen it. Also gives a larger surface to attach the roof to.  jefferson