Metal Casting Zone

Hello, I am new to this list and am not sure if this will post or not. Anyway, I wouldlike to ask if anyone has used something oter the silver solder to make a master for inversment casting.
Thanks in advance,
Tom Stoltz
Tom’s Turnouts & Trackwork
Dresden ME
www.tomsturnouts.com

Whaddya know? Another Mainer! Wohoo! Welcome Tom, I am up here in Orrington, not too far away. I have not done any investment casting yet, but for stuff like you are doing it would be about right. I do sand casting and lost foam.
As far as a master, do you mean that you want to make a mold to, say, cast multiple wax pieces from so you can make a lot of copies? Just about anything would work as an original. To make a copy of something, you cover it in RTV or silicone to make an original mold, and then inject wax into the silicone/rubber mold to make copies. Tree the wax pieces up, dip them in investment material, melt/burn out the wax, and pour in the metal. Horribly simplified, but that is the process in a nutshell.
If it was a one off piece, or just a prototype, you could also make the original directly out of wax and cast that. Depends on the application, I guess.
If it was a fairly simple piece, you may want to look into something called "delft clay". It is used sometimes for jewelry, and you do it almost the same way that you would do a sand mold, just on a smaller scale.
If there is anything I can do to assist, just let me know.

Hi OddDuck,
I have been using a commercial caster to do my work, but I can’t get the info I need from him. What I’m looking for is a different medium – other than silver solder – to make my masters. The reason is a have to sculpt the shape I need and it is trial by error. I have tried refractory cement, but when I pre-heat it, it shrinks away from the rail. The same is true for refractory mortar. Now I am trying a manifold repair material with the mortar for a final coating. I was hoping someone on this list would have some experience.
There are a number of pieces I would like to have casted for my turnouts, but still have a whole lot to learn.
I have noticed there is a separate section on this forum for investment casting – do messages cross post or should I be posting there?
Tom Stoltz
www.tomsturnouts.com

You can look through this site. It has a lot of videos on mold and pattern making, it may give you some ideas.

www.freemansupply.com/index.htm

If you add silica sand to your refractory material it may cut back on the shrinkage.

Are the parts you are trying to mold the angled pieces in the middle of the crossovers?(frogs? not sure of the nomenclature) Are you trying to do them yourself due to costs, quality control, or turnaround time? Do you have a pic of the part you are trying to do? A lot of questions, but it helps to have an idea of the part to help with the exact application. This looks like an ideal setup for making yourself a wax extruder to make rail-shaped wax pieces, which you could easily join up , dip, burnout and cast.

I’m having the frogs cast because they are very labor intensive to produce by hand. If you look at my web site under turnouts, scroll down and you will see a close up of the frog. I have added what I call the insert – I cast it from resin. What I want to do is cast the frog with the insert included. I have been successful with one, but with that one, the master was made using rail and refractory cement. It takes a bit of milling to get the shape for the insert and the refractory cement is hard on the mills – also it is crumbly after I pre-heat it to 350°F and it also shrank away from the rails. Some of the crumbs pulled out when the caster made the mold. I can get back from him if he can clean it or not…
So I am trying a refractory mortar which is very nice to work with, but it also shrinks. Yeah, I do go back and refill, but it is a repeating process.
Enter the manifold repair mix. Its final form is like a pumas stone (very porous); however, it seems to hold to the metal and provides a good foundation for the refractory mortar. – That’s where I am. I was hoping there would be some product out there someone on this list would know about.
I also have some issues with my caster on QC and sharing of knowledge. I’m looking for answers.
I can post more pictures if you can tell me how and where…
Tom Stoltz
In Dresden ME
www.tomsturnouts.com

At least I got the name of the part right. Yeah, looking at that pic, I think your best bet is going to be molding up an original from wax, and doing a master rtv mold off of that. You can get machinable waxes fromm Freeman's, like Jammer mentioned. At the scale you are working with, shrink will be a negligible problem. To go cheap and simple, here's what I would do, if it were me. First, make a two part mold from plaster of paris of just some straight sections of track. Do several sections at a time, so you can make multiple sections of wax track at once. To compensate for the shrinkage of the wax, and then the shrinkage of the metal, I would coat the track sections that you use to make the mold in a few coats of lacquer or paint, to build them up just a little. There are all kinds of examples of making two part POP molds, don't sweat that at the moment. After you get your mold made, you can use it to cast as many wax rail sections as needed. Build the frog and insert out of the wax railing, and make a silicone mold of that. Inject wax into this master mold to get copies of the frog. "Tree" these up onto a common sprue (The channel that you pour the metal down) and dip/pour the investment. You can get commercial investment products, but they require a bit of equipment setup to work well. A quicker (and cheaper) investment is just POP and fine silica sand. Burn out the wax, melt the metal, and pour away. The nice thing about doing it this way is that you can make one or a couple dozen at a time. Make one at a time and tweak the original until it is exactly what you want. Sounds complicated, I realize, and you are going to have to build a lot of equipment and have lots of trial and error along the way, but it is absolutely doable. And once you have this application down, you will come up with hundreds of other projects that you can do with it. For further reference, the guy who did this thread (Abby) backyardmetalcasting.com/forums/viewtopic.php?t=2592 is the guru of investment at BYMC. He does train parts as well and his work is quite impressive.

Thank you for the info. I am not really looking to increase the work I do, but rather decrease it by subbing out the casting. I do have to make the master and my caster likes to use hi temp vulcanizing rather than RTV which is where I would like to change my process. Shrinkage is a factor because of the triangular shape of the frog. I use the rail for the master and would like to increase its size by about 4%, but I don’t think lacquer would do because the vulcanizing requires 350°F. Also the ‘insert’ part of the frog takes me a bit of sculpting so there I need a material that is easily shaped, can be added on to, and heated to 350° without shrinkage. The shrinkage in this case is pulling away from the rail leaving a gap and loosening the bond between the insert and rail.
Tom Stoltz
In Maine

Hi Talvin48
Just been reading your notes on your problems with the frog for your turnouts. I am envolved with model trains myself and know the part you wish to manufacture.Maybe some of my jewellery trade knowlege may assist you here.I know the rubber that you caster uses. However, there is another that could be used. Firstly the master of the rail could be made in a larger code of rail maybe, say code 100 instead of 75. Code 100 rail may shrink down to what you my need .If not another aplication to think of is to have the rail master you make total in metal electro plated. Ask the plater to plate a heavy coating on the item and tell the plater to do this as a normal coating will not deposit enough on the item to allow for the shrinkage percentage 4% that you are planning for from master to casting. Take the plated master and make a wax injection mould by using RTV rubber. Castaldo (A well known supplier of jewellery rubber products) has a rubber called pink liquid cast a two part RTV rubber and I know from my use of this product it work very well. Beautifull repoduction of detail and makes nice waxes. Another product you sould try for the mauufacture of master parts that are dificult to shape is Milliputty SOLD IN HOBBIE STORES There are 3 types and the best is the superfine . Mix part a and b together and you have a nice fine white clay to use for 2 hours to sculpt any shape and fill holes. In 24 hours you have a master as hard as hard and this product can be then drilled, ground, filed, and best of all valcanized in rubber quite ok at 150oc for 1 hour . It does discolour and is rather week if in small thin sections. And breaks apart after valcanizing a bit. But maintains it shape quite well in the mould while valcanizing . But for my models its great .I have sculptured figures from this material.and many model parts, If the part is fine and in Miliputty I make a mould in RTV. Hope this helps JOHNCAST

After rereading my last post I guess I wasn't real clear. When I mentioned coating a rail with paint or lacquer, that was to make the plaster mold to cast oversize rail sections out of wax. You are right, that wouldn't stand up too well to temps doing it the way you are doing it. Just out of curiosity, is your caster in-state? If they are using vulcanized rubber they must be spin-casting the parts for you. There was a model ship kit company in Searsport that did that, can't think of the name at the moment. I should know it, I used to fix their copier all the time.
For what it's worth, and I know it's a bit of a drive, but I would be willing to give you a hand trying some investment casting to at least produce the master that your caster can use to make the permanent mold. Just what I need, another project, but what the heck. That way you wouldn't have to frig with building your own furnace, etc. I agree, it is a lot of trouble to go through for a piece or two that someone else can crank out by the hundreds.
If you are interested, shoot me an email at oddduckfoundry(at)msn.com.