I’m building up the pit wall to a CMR turntable by stacking rings of 1/8" styrene. Unfortunately, I wasn’t able to make it as smooth as I’d like, so part of it looks like this:
I tried to skim-coat the wall with Squadron to even out the depressions, but I’m still left with random imperfections that subsequent priming and painting magnify. Am I expecting too much from Squadron? If I am, could someone suggest an alternative? If my technique is the problem (thin with Testors Acrylic Cement, apply 1-3 thin coats, and wet-sand with 600 grit), could somebody suggest the right approach?
My first thought would be to slowly and carefully wet sand the surface you do have, at least initially probably using something faster acting than 600 grit, really thoroughly, so that the surface you are starting out with is as smooth and even as it can be. Indeed if you do a really great job at this it may be that you could do without a skim coat and a simple paint job might be enough.
I assume what you’d need is a sanding block with a rounded surface somewhat close to the interior radius of your surface there. A jar, bottle, or large can might be just the thing. You may well have the “tool” you need in your recycling bin.
How about gluing a strip of .010" styrene to the inside of the curve the same height as the overall assembly? Then the only gaps you would need to fill would be at the top where the sides and top meet, and that should be easy to smooth out since it will be a flat surface.
My only caution with .010" styrene is that it can be distorted if you use too much solvent type glue. CA might be a safer bet.
The .010" liner sounds like a good solution if your turntable can accommodate the slight loss of pit diameter.
Otherwise, use either coarser sandpaper or a half-round mill file initially to take out the worst of the irregularities, then use progressively finer grits.
If you have a suitably long and sturdy blade, dragging it around the inside face of the pit, with the blade perpendicular to the surface, will also remove excess material effectively.
To thin the filler putty, use lacquer thinner or a similar solvent, and it may help to “prep” the styrene with a coat of lacquer thinner, too. I know that such a “prep” treatment makes for a much better bond when cementing styrene with contact cement. Work on small areas at a time, as once the thinner has evapourated, it needs to be re-coated.
The liner method would seem to be the way to go, IF the inside diameter is big enough. One way to smooth down the inside would be to use a sanding drum on a Dremel, if the drum is at least as wide as the pit wall is tall. Better yet would be if you had the Dremel drill press attachment and locked it down so the Dremel was held steady and you moved the pit ring assembly to samd it to an even finish. If it ended up too big, then you could add the liner to bring the inside diameter back to where it needs to be and end up with a nice smooth inside finish - there’s probably be 3 seams, unless you cut the line from a larger than the typical EVergreen size sheet of styrene, in which case there would be but one gap where the ends met.
I am inclined to try the sanding first and if not satisfied do as mentioned by veneering w/ styrene.
I assume you are looking to get a formed concrete appearance. If some sanding still shows imperfections, remember that when the real thing was formed for the conc pour, most of the lines from the forms would show anyway. Some of these imperfections may prove to be an advantage, once distresed and weathered may actually look better than an absolutely berfectly flat wall. Some vertical scribed lines between the horizontals would show definition of forming boards as well. these should be scribed and samded so not so pronounced.
The liner ring sounds good, if not, try bondo in the tube, picked up at auto parts stores or walmart, this stuff comes out fairly thin and could be done in a few coats. Also, if you are trying to represent concrete, some imperfections won’t be bad .Another trick is to use a sand colored texture paint, give it light coats to fill in seems then lightly sand smooth, you’ll have enought texture to simulate qoncrete.
The “Bondo” in a tube is actually automotive glazing putty, not to be confused w/ Bondo/ cataylist filler. 3M glazing putty is what I use, does about the same job for our needs, glazing putty should only be placed in thin layers, too thick and takes quite long to dry and may not work as intended. This is formulated to fill minor scratches and imperfections prior to wet sanding and priming.
This glazing putty is far superior to Squadron putty and a tube will last many, many years.
I agree and had that thought with my skim-coating so far. But I concluded I was rationalizing–it looked pretty bad and I was simply trying to get on with it. I’ll probably try sanding first, as I have some tight clearance spots with the TT bridge, and the styrene will probably be too much. But I won’t try for a perfect appearance.
Actually, CTValleyRR, I haven’t had a chance to get back to it since starting this thread, so I’ll take a look at Woodland Scenics foam putty. Thanks.
Another poster asked how long it should take to ballast track. At this point, my answer would be “about half as long as it’ll take me to build this turntable.”
