Question for any casting guru

IN process of making mold now, water tank, actual dimensions about 1 inch across and equally as high, wood tank,but I need more than one and standing
downstairs at the mill scribing the board lines isn't what I want to do. Ok, wood form made, but now comes the question, what medium to mold them in? I'm leaning toward hydrocal, cheap and easy to work with, even after it's cast. They won't be touched once they're in place, part of the scenery, in out of the way places. Not elevated, they stand on squat poured foundations, elevation comes from the hill they're on, above the residence they serve. Hydrocal good? Resin? (IF resin, that means I've gotta make a plug to fill part of it, that would be a lot of resin.)
Rich
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Hydrocal would be just fine however you want to make sure the mold is made from a real stretchy RTV. Not that others wouldn't work but a stretchy mold will make sure no plaster gets broken. I think you need to use a mold release but forgot what.
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Using a latex mold compound, brush on type, only needs ten coats. Waiting on second coat to dry now. Maybe by Thursday.
Mold release I've used for rock molds is nothing but a couple of drops of detergent in water, It's worked good so far. No detail protruding, I'll add the tank bands later, (black monofilament).
Rich.
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greybeard spake thus:

So why do model railroaders automatically think "Hydrocal (R)(TM)" when they think of casting things?
Use ordinary plaster (plaster of Paris); it's cheaper, available everywhere (no need to go to a hobby store) and works just as well for most applications. Sure, it may not be quite as rock-hard as the more expensive stuff, but since you say it won't be handled, no problemo. Takes paint extremely well.
As the other reply said, just make sure you have a stretchy-enough mold. Either RTV or urethane ought to work OK here.
One trick I learned: to prevent the inevitable bubbles, brush the mold with alcohol (rubbing alcohol is fine, or isopropyl) before casting. This wets the mold so bubbles can't form.
--
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'Cuz I've had a little problem with plaster of Paris, chipping on some of the rock molds, thinking that something harder might be a little better here.

Been using Woodland Scenics, colors are nice, maybe I thin them too much, they're more like an ink. Thinking some kind of enamel, something that will harden the surface, or possibly a clear coat, (Dullcote?) might have the same effects.

If I can find it, I've got a bottle of Kodak Photo-Flo, which is the supreme wetting agent. (Pre-soak for film developing, also for wetting fiber based papers.) Woodland Scenics says to spray the mold, I prefer to fill it and dump it out just before putting the plaster in, no missed spots that way. Alcohol would have the same effect, reducing the surface tension of the water for more effective wetting.
Rich.
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greybeard spake thus:

Well, I can tell you I've made plenty of casts using ordinary plaster with no such problems. For example, homemade 55 gal. barrels.

Again, think outside the "Official Model Railroad Product" box. I use Delta Ceramcoat acrylics, which you can buy anywhere (at least in the U.S.), which will paint virtually anything, certainly plaster, and come in a zillion colors. Cheaper, too.

Photo-Flo might work (but of course, you can just detergent, no need to buy Official Photo Stuff here!); I didn't use it because I didn't know if the soap might interfere with the plaster setting. Alcohol for sure doesn't, as it just evaporates.
By the way, about your idea of adding the bands later with monofilament: I'll bet you could include them in the mold and that they would survive removal after casting. The bands on my oil drums come out just fine, and they stick up from the surface, essentially creating an "undercut". You could try it and see.
--
To the arrogant putzes at NBC:

Do we call the country Italia? Is its capital Roma?
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Rich wrote:
"IN process of making mold now, water tank, actual dimensions about 1 inch across and equally as high, wood tank,but I need more than one and standing downstairs at the mill scribing the board lines isn't what I want to do. Ok, wood form made, but now comes the question, what medium to mold them in? I'm leaning toward hydrocal, cheap and easy to work with, even after it's cast. They won't be touched once they're in place, part of the scenery, in out of the way places. Not elevated, they stand on squat poured foundations, elevation comes from the hill they're on, above the residence they serve. Hydrocal good? Resin? (IF resin, that means I've gotta make a plug to fill part of it, that would be a lot of resin.) "
What do you need to scribe it for? Why do you even need to cast them? Just use a length of styrene tube and laminate some evergreen scale car siding on to it.
David Nebenzahl wrote:
"So why do model railroaders automatically think "Hydrocal (R)(TM)" when they think of casting things?"
Cause we've been brainwashed by the Milwaukee Mafia into believing it's the only form of plaster there is? They're obviously on the take from US Gypsum.
"As the other reply said, just make sure you have a stretchy-enough mold. Either RTV or urethane ought to work OK here."
Could just use a two piece or a cut mold.
Eric
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Using the dividing head in the mill, a few holes one side or the other from the zero hole will give a slight variation, as one would see in the real tank itself if it still existed. These tanks were hand made locally out of rough sawn white oak, I would have to guess sometime in the 1920 - 1940 period.

The plastic look is something I go out of my way to avoid at all cost, Casting because as it has been said in a foundry book I have, "The easiest way to work metal is to not work it at all", referring to complex shapes being easier to make a wood pattern, make molds and pour than try to machine from a billet. I'll be making six, how many will actually be used is still undecided.

Because using the hardest medium available when you have details that might be wiped off with a thumb just seems to make sense. If I knew someone that was bedding a machine, I'd have them try Por-Roc, but that's going a little expensive.

Seam lines are sooooo unattractive. With the materials that are available today, there is no reason to accept a compromise instead of what you really want. With the latex/RTV/silicone rubber mold materials made today, having seam lines can be easily avoided. Probably it could be said I want to do the hard part once, not six times.
Rich
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In a message on Sun, 26 Feb 2006 13:28:02 -0800, wrote :
DN> greybeard spake thus: DN> DN> > IN process of making mold now, water tank, actual dimensions about 1 inch DN> > across and equally as high, wood tank,but I need more than one and standing DN> > downstairs at the mill scribing the board lines isn't what I want to do. DN> > Ok, wood form made, but now comes the question, what medium to mold them in? DN> > I'm leaning toward hydrocal, cheap and easy to work with, even after it's DN> > cast. They won't be touched once they're in place, part of the scenery, in DN> > out of the way places. Not elevated, they stand on squat poured DN> > foundations, elevation comes from the hill they're on, above the residence DN> > they serve. Hydrocal good? Resin? (IF resin, that means I've gotta make a DN> > plug to fill part of it, that would be a lot of resin.) DN> DN> So why do model railroaders automatically think "Hydrocal (R)(TM)" when DN> they think of casting things? DN> DN> Use ordinary plaster (plaster of Paris); it's cheaper, available
Hydrocal in 80lb bags is as cheap (if not cheaper) than plaster of Paris. *Serious* model railroaders don't buy the silly little cartons of Hydrocal from Woodland Scenics :-). I got me a big bag of the stuff from a 'local' masonary supply place and have it sitting in a moisture tight bucket (originally meant to hold Chlorine tablets for pool cleaning).
DN> everywhere (no need to go to a hobby store) and works just as well for DN> most applications. Sure, it may not be quite as rock-hard as the more DN> expensive stuff, but since you say it won't be handled, no problemo. DN> Takes paint extremely well. DN> DN> As the other reply said, just make sure you have a stretchy-enough mold. DN> Either RTV or urethane ought to work OK here. DN> DN> One trick I learned: to prevent the inevitable bubbles, brush the mold DN> with alcohol (rubbing alcohol is fine, or isopropyl) before casting. DN> This wets the mold so bubbles can't form. DN> DN> DN> -- DN> To the arrogant putzes at NBC: DN> DN> Do we call the country Italia? Is its capital Roma? DN> Were previous Olympics held in Moskva, Muenchen or Athine? DN> Do we call it the "Shroud of Torino"? DN> DN> No! DN> DN> So learn to speak English already and call it Turin. DN> DN> - from someone's blog DN>
\/ Robert Heller ||InterNet: snipped-for-privacy@deepsoft.com http://www.deepsoft.com/ ||FidoNet: 1:321/153 http://www.deepsoft.com/~heller /\
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On Sun, 26 Feb 2006 12:36:23 -0600, "greybeard"

Just a suggestion for future projects of this type. Why not use wood ? Nothing looks more like wood than the real thing. Scale stripwood glued to a 1" wood dowel or a length of plastic tubing. Make a section slightly over 6" and then cut into six pieces. You can stain all the stripwood first and and after that dries I'm sure you can build it while you're thinking about doing a mold. You could probably do this in a couple hours after the wood is prepared. Won't need to scribe any lines and there will be a variagated look as the strips will have a slightly different grain and density. Even scribing lines wouldn't be bad on a little project like this.
Of course , if you plan on doing a large number the mold is the way to go... or if you just want to do it that way :-)
I scratch build a lot and sometimes for other people. Now talk about scribing lines , I'm building a passenger terminal for a fellow with a very large O scale layout. The main structure is 60" long and 32" wide with a separate platform that measures 18" x 30" The main structure is 1' x 2' cut stone. I'm scribing all these lines. Whew !! That comes to approx 14,000 stones. Also , it has 24 windows with masonry Roman arches with Keystones and row locks. Also has corner quoins. Actually , it sounds worse than it really is. Last night I scribed one wall (12" x 60") in about 3 hours. That included the first coat of white primer sealer. I've never undertaken such a large project but it was actually a lot of fun in the beginning. But , I do have a lot fun to go :-( Good luck with with your project. Sounds like you have it by the b***s.
Ken Day
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wrote:

Made the mold plug out of plain, straight grained hard maple, then scribed the lines using the dividing head in my mill. 24 turns each way for one scribing, 40 planks around the circumference, lots of spinning cranks. Bored recess in top to leave lip above top planking, top planking made from scribed sheeting, Looks like it'll be good once the monofilament "bands" are around it, but the plaster is taking it's time to not have that "wet" feel. Once it feels dry then comes the color. Interesting, but for some reason, meaning I probably didn't wax the wood thoroughly, the latex stuck to it in some tiny spots, gives the same impression that I had when looking at the trash on the top of the real one and thinking "I'm drinking water out of this?". Used a very fine rotary wire brush in a die grinder to raise the roughness of the wood, trying to make it look more like rough sawn lumber, think it's ok. I'll know when it's not white.
So far it looks good, even the poured concrete base that some of them sat on, I made a separate mold, but now I'm looking for some way to simulate the stone masonry that some of the older ones were. Probably gluing coarse ballast on the sides of the mold plug, not sure yet.
Rich
"If it ain't fun, don't do it!"
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On Sat, 11 Mar 2006 18:45:57 -0600, "greybeard"

I would enjoy seeing a pic of your project. Are these for a mill of some sort ? We need more talk about actual model railroading in this group and more sharing of ideas and even pictures.
Ken Day
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wrote:

These were 5000 gallon tanks, most used more in residential service, and in places where other methods of storing water weren't practical. The one we had, the tank and well were each about 300 feet, maybe a little more, from the house, but in different directions. The well was down on the flat, one horse Briggs driven pump, to the north of the house. The tank was to the west of the house, and probably some thirty to fifty feet higher in elevation. It only served one house, but there were quite a few others like it in some places. From what our lanlord told us, they were made locally, but my guess would be they were made sometime in the 1930's or early 1940's. From what I've been told none of them exist anymore, relying on mostly memory, and knowing how much it held. The proportions look about right and they're usually in some place they couldn't be seen anyhow. Forty boards around it may not be enough, but the proportions look to match my memory fairly well. Color might be fun, they were made from Burr oak, dark to begin with, but with no demand for it, cheap and hard, a good material. Never painted, oiled or anything else, bare, rough sawn oak.
There are times that one kicks one's self for not using a camera more, but I wasn't really into scale modeling anything then. Oh well.
Rich
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