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Model Forum / General / Railroads / January 2007Casting question
No, it's got nothing to do with American Idol or Broadway. I've googled and looked at bunches of sites without finding what I'm looking for, so I'm throwing myself on the mercy of the court of Usenet (in other words, I'm desperate and am asking here as a last resort). OK, here's the deal: I'm trying to make the simplest casting in the world, basically a chunk o'lead to put into a diesel (Rivarossi E8) to weight it down. Made a really nice master out of wood. Tried to make a plaster mold with it: of course, even though I'd oiled the wood thoroughly, it stuck to the plaster so tightly I had to bust the mold to pieces to get the master out. So here's my question: I know how to make the casting once I get my plaster mold (be sure to dry to mold to remove all moisture, etc., etc.). What I'm having trouble with, obviously, is making the damn mold. (It only needs to be a simple 1-piece mold, so I don't need advice on making full molds, parting lines and such.) Anyone familiar with casting here who can help? Vaseline? Grease? Pull it out as the plaster is setting? It occurred to me that I could also go down to the local foundry (yes, there actually is one in town here, still functioning) and try to score a little bit of casting sand. Or is there some easier way to make a plaster mold from a wood master? The trick is trying to extract the master from the mold after the plaster sets.  SignatureJust as McDonald's is where you go when you're hungry but don't really care about the quality of your food, Wikipedia is where you go when you're curious but don't really care about the quality of your knowledge. - Matthew White's WikiWatch (http://users.erols.com/mwhite28/wikiwoo.htm) >So here's my question: I know how to make the casting once I get my >plaster mold (be sure to dry to mold to remove all moisture, etc., >etc.). What I'm having trouble with, obviously, is making the damn mold. Lay plastic wrap over the wood and pour the plaster over it into a large ring with the wood in the center. When you take it out, peel the plastic wrap from the plaster. If a bit of it stays, so what? Just pour the lead anyway and the plastic won't hurt a thing. I use Pam, baking spray for most castings. Works a treat. -- Ray Ray Haddad spake thus: >>So here's my question: I know how to make the casting once I get my >>plaster mold (be sure to dry to mold to remove all moisture, etc., [quoted text clipped - 6 lines] > > I use Pam, baking spray for most castings. Works a treat. Hmm; don't like the plastic idea so much (what with the inevitable fold lines and all). Pam sounds more promising. Are you saying you use it as a mold release agent for masters? I thought soaking (literally) my little wood block in motor oil for several hours would do the trick. Evidently not. SignatureJust as McDonald's is where you go when you're hungry but don't really care about the quality of your food, Wikipedia is where you go when you're curious but don't really care about the quality of your knowledge. - Matthew White's WikiWatch (http://users.erols.com/mwhite28/wikiwoo.htm) >Ray Haddad spake thus: > [quoted text clipped - 12 lines] >lines and all). Pam sounds more promising. Are you saying you use it as >a mold release agent for masters? Yes. I use Pam, liberally applied. Works great. The plastic wrap can be shrunk with a heat gun a little to tighten it up. In fact, a toy Vacu-Form can be used to make a first negative mold which can be used to make a better master from plaster than one made of wood. There's actually a book out on using that technique. http://www.abebooks.com/servlet/BookDetailsPL?bi=692988723&searchurl=bx%3Doff%26 ds%3D30%26bi%3D0%26y%3D0%26tn%3Dvacuum%2Bforming%26x%3D0%26sortby%3D2 or use http://www.abebooks.com and search for ISBN 1878087223 >I thought soaking (literally) my little wood block in motor oil for >several hours would do the trick. Evidently not. That would probably taint the plaster. Use the same book search engine and search on the words "plaster casting" in the title and then, clear that, and use the same terms for searching the keywords. -- Ray > Use the same book search engine and search on the words "plaster casting" I got a reference to this groupie named Cynthia Plastercaster, but she was doing 1:1 casts, not models. SignatureSteve Ray Haddad spake thus: >>So here's my question: I know how to make the casting once I get my >>plaster mold (be sure to dry to mold to remove all moisture, etc., >>etc.). What I'm having trouble with, obviously, is making the damn mold. > Lay plastic wrap over the wood and pour the plaster over it into a > large ring with the wood in the center. When you take it out, peel > the plastic wrap from the plaster. If a bit of it stays, so what? > Just pour the lead anyway and the plastic won't hurt a thing. I forgot to say that it's not just a plain block, but has a slot cut in it to clear a screw boss in the loco, so it'd be tricky to try to get plastic wrap around it. SignatureJust as McDonald's is where you go when you're hungry but don't really care about the quality of your food, Wikipedia is where you go when you're curious but don't really care about the quality of your knowledge. - Matthew White's WikiWatch (http://users.erols.com/mwhite28/wikiwoo.htm) > I forgot to say that it's not just a plain block, but has a slot cut in it > to clear a screw boss in the loco, so it'd be tricky to try to get plastic > wrap around it. You might try a layer or two of aluminum foil. You should be able to adapt it to the shape of your master pretty well. Be sure you don't have any undercuts or your master won't draw -- better to have a slight taper. I've done it myself and it has worked quite well. Jim Bright here as a last resort). > OK, here's the deal: I'm trying to make the simplest casting in the world, > basically a chunk o'lead to put into a diesel (Rivarossi E8) to weight it [quoted text clipped - 11 lines] > > Anyone familiar with casting here who can help? 1) You don't mention draft angles - are the sides of your master perhaps too parallel? 2) Googling yielded a thread amongst potters with some ideas at http://www.potters.org/subject95359.htm 3) My own experience with plaster moulds for casting lead has not been good - I never seemed to be able to get the plaster dry enough to avoid generating steam when I poured in the lead resulting in voids, or causing the mould to crack - I'm probably too impatient. I therefore make most of my lead weights in wooden moulds and avoid the master step. To avoid getting voids, I keep the wood as dry as possible and don't use any release agent. I don't usually worry about draft angles and instead make the mould partially disassembleable to remove the finished casting. As you describe, I find that for simple weight shapes, I usually can design an open top 5 sided mould to allow a simple pour of the lead. Geezer Geezer spake thus: > here as a last resort). > [quoted text clipped - 16 lines] > 1) You don't mention draft angles - are the sides of your master perhaps > too parallel? After I retrieved my wooden master and looked at it more carefully, turned out it had a negative draft angle. I reworked it with a file and am going to attempt another mold with it. Also found my official wax release agent, which I'm going to schmear over the master in hopes it'll keep the plaster from sticking to it. > 3) My own experience with plaster moulds for casting lead has not been > good - I never seemed to be able to get the plaster dry enough to avoid > generating steam when I poured in the lead resulting in voids, or causing > the mould to crack - I'm probably too impatient. Yes; a few hours of baking at around 300° or so should do the trick. SignatureJust as McDonald's is where you go when you're hungry but don't really care about the quality of your food, Wikipedia is where you go when you're curious but don't really care about the quality of your knowledge. - Matthew White's WikiWatch (http://users.erols.com/mwhite28/wikiwoo.htm) > Geezer spake thus: > [quoted text clipped - 15 lines] >>> >>>Anyone familiar with casting here who can help? If it is a 'one-off' casting, have you thought about doing a lost wax casting? Shape the wax make a plaster mold around it to contain the lead then pour. SignatureFrank Rosenbaum Please note my new email address: farosenbaum at comcast dot net. Please support the following train meets if you can Gratiot Valley ( www.gvrr.org ) in Macomb Michigan in March and November and the Kalamazoo Model Railroad Historical Society ( www.kmrhs.org ) at the Kalamazoo Fairgrounds in Kalamazoo MI in October. Also check out the Westchester Model Railroad Club's train meet in Greenwich CT in November and March. Visit this web site to see my bridge and the KMRHS http://tinyurl.com/7uqdr Frank Rosenbaum Frank A. Rosenbaum spake thus: >>Geezer spake thus: >> [quoted text clipped - 19 lines] > casting? Shape the wax make a plaster mold around it to contain the lead > then pour. No, but if what I'm doing doesn't work, I may try that: I've always been curious about lost-wax casting. I guess my mold would be simple enough that I could just pour the lead in on top of the wax and let it flow out, right? SignatureJust as McDonald's is where you go when you're hungry but don't really care about the quality of your food, Wikipedia is where you go when you're curious but don't really care about the quality of your knowledge. - Matthew White's WikiWatch (http://users.erols.com/mwhite28/wikiwoo.htm) > Frank A. Rosenbaum spake thus: > [quoted text clipped - 28 lines] > I guess my mold would be simple enough that I could just pour the lead in > on top of the wax and let it flow out, right? I believe that wax would just vaporize as the lead came in contact with it. It would be best done outside or with the Templo lead that is available. I would also pour it in from one end so the lead doesn't cover the wax over and cause it to explode. Maybe have vent holes in the bottom of the casting box to let any wax that just melts out. Good morning David; > No, it's got nothing to do with American Idol or Broadway. > [quoted text clipped - 25 lines] > mold from a wood master? The trick is trying to extract the master from > the mold after the plaster sets. I took a machine shop course in High School, and it contained a small foundry. Those who used it generally melted down pistons for the aluminum which was subsequently poured into blank moulds. I recall people using casting sand sprinkled with bone meal dust. The only other alternative is to scavenge lead-acid batteries, cut the lead slats to size and solder them together. It's been 30 years and my travels have had little to do with such projects since. Sorry if I can't be of more help. Cheers, John > Good morning David; > [quoted text clipped - 40 lines] > Cheers, > John Don't do that - the fumes from the battery acid given off will do nasty things to the cat and any other living creatures in the vicinity. Good afternoon Greg; >> Good morning David; >> [quoted text clipped - 56 lines] > Don't do that - the fumes from the battery acid given off will do nasty > things to the cat and any other living creatures in the vicinity. Good point, as it's nasty stuff with which we wouldn't fare much better than the cat. I was thinking of the scenario of the acid already removed and the cells soaked in a sodium bicarbonate solution before bringing it home. Thanks. Cheers, John You might use sheets of lead flashing (not as easy to find as it used to be, however) or lead shot glued together. Avoid the casting altogether. >You might use sheets of lead flashing (not as easy to find as it used to be, >however) or lead shot glued together. Avoid the casting altogether. I was going to suggest shotgun pellets (or small split shot fishing weights) and epoxy but that's a permanent addition to the shell. Works great, though, when you need to add it without too much fuss. -- Ray > I was going to suggest shotgun pellets . . . . . . but you have to find old ones with lead shot, not steel. SignatureSteve > No, it's got nothing to do with American Idol or Broadway. > [quoted text clipped - 32 lines] > > - Matthew White's WikiWatch (http://users.erols.com/mwhite28/wikiwoo.htm) Why not just make the mold out of wood? I assume it's just a shaped block? It needs to split some way to get the casting out so something like a profile cut in timber of the right thickness can have ply/hardboard sides screwed on which can be removed for casting extraction. Finish shaping with a coarse file/rasp in a vice. Regards, Greg.P. > > No, it's got nothing to do with American Idol or Broadway. > > [quoted text clipped - 42 lines] > Regards, > Greg.P. I read some earlier postings and saw the one about a slot to clear a chassis screw - make the casting without provision and drill and chisel a suitable depression to suit. Lead is soft! > Anyone familiar with casting here who can help? I recommend http://www.tiranti.co.uk/ for tools and materials. SignatureVenlig hilsen Erik Olsen http://www.modelbaneteknik.dk/ Plaster tends to blow up unless it's been baked forever. I have made simple molds (for lead) from wood. The wood gets burnt but a little water keeps the fire from starting. Make sure the lead has set before adding any liquid or it will explode. Safety glasses and a leather welders apron help while doing all this. /wikiwoo.htm) Hi Dave: If you are using a wax pattern, heat it up after the plaster has cured and pour out the wax before you pour in the molten lead, to reduce the flames when the wax boils and catches fire. Also, if you add some fine sand to the plaster it will make it weaker and easier to remove. One of the guys I work with built a furnace in his backyard and he told me that "greensand" is actually regular sand mixed with another mineral that is actually or very close to pulerized kitty liter. You can also carve a pattern out of small cell styrofoam, then leave the styrofoam in the mold, and the molten lead with burn it to a thin film, or dig it out of the mold before you pour, if you wish.. Or you could just pour a simple little brick of lead close to the size you want, then file and drill it to the finished shape you need. BTW, if you've ever dissected a modern car battery, you've seen that there is no usable lead in the plates, only a few ounces from the two external posts and the connections to the plates. Wayne > No, it's got nothing to do with American Idol or Broadway. > [quoted text clipped - 25 lines] > mold from a wood master? The trick is trying to extract the master from > the mold after the plaster sets. |
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