Sand Casting or lost wax investment for thin complex cast iron parts?

Hi

I am investigating the feasibility of building a miniature 1/3 scale 1925 Steam Wagon.
I have copies of the original factory drawings for the specific Steam Wagon I would like to build.

The factory drawings identify over 60 patterns for castings. Many I parts I can fabricate or machine but there are more than a few that will require complex castings. Attached are a couple of samples. The engine and the wheels. Both include castings with wall thicknesses of only 3/8 inch (some places are down to 5/16 thick at full scale). At 1/3 scale, this would be only 1/8 inch. I can probably get away with 3/16 inch on the model but any thicker will have a cascading effect on the size/fitment of other parts.


Attached are representative examples of the complex castings. At 15inch scale across diameter, the rear wheels would be the largest castings.




The full size wagon castings would have been in sand. I don't think I could reliably use sand castings for a miniature version. Even if I could fill the mold, I suspect the cast iron would be chilled white to be unmachineable and too brittle. I think lost wax investment casting would be a better option.

If that is correct, the next problem I would have is getting the ceramic slurry. Not something I can buy off the shelf in New Zealand. I would also need to make/buy and setup the equipment needed for a small foundry.

I have looked at the home/amateur websites but relatively few have delved into investment casting.

Am I on the right track?
Any feedback welcome.


Dazz

I think lost wax can be done with 3d printed plastic positives. maybe they can even 3d print wax.
Bill D.

I glanced at some posts on this site: AlloyAvenue network Seems to be various choices for brass/bronze. I didn't dig for cast iron though.

Bill D said:

I think lost wax can be done with 3d printed plastic positives. maybe they can even 3d print wax.
Bill D.

Click to expand...

Yeah, PLA printed parts can be used for lost "wax" methods because it's non-toxic when it vaporizes. You can use the metal itself to vaporize the plastic if you print a thin enough shell. That's not looking to be a good option in this case because of all the hollow sections and undercuts.

Might be able to print thicker PLA pieces and bake it out in a kiln though, same as lost wax but much higher temperature to evacuate the plastic. You'd have the disadvantage of the printer layers giving you a fingerprint-like surface finish unless you print oversize and carefully finish by hand.

One-third scale is pretty big so these would be fairly sizable patterns and cores, not economical for commercial lost-wax casting which is inherently very high overhead. Cast iron is extremely fluid and will pick up small details in sand molds, which is why so much ornamental work 100 years ago was cast iron. And for mechanical parts it's a lot better than brass. Check with an iron foundry and then learn to make patterns.

About 18 months ago I began the process of setting up an iron foundry to cast relatively thin cast iron patterns for sale as straight edges. You should and maybe do know that casting iron is much more difficult than casting brass/bronze/ aluminum. You can expect to have hundreds of hours in building a furnace, flasks, molding equipment, crucible handling gear, sand mulling equipment, refractory materials and so on and then the fun of learning its intricacies. After many pours and melts you will start to reliably get usable parts.

I am not trying to be discouraging in any way. But you are choosing the most difficult metal somewhat commonly cast on a small scale and then choosing a difficult pattern to cast—-just like I did ;-)

You would do well to find a mentor who is doing something like what you are proposing to do. Individual casters are few and far between. I am aware of two or three guys in NZ who you might try to find and talk to.

I think it is feasible to cast the parts you show in in sand. You may need to tweak your alloy to do it. Casting in itself is a fascinating and rewarding pursuit. If you "have the fire in your belly" go for it.

Denis

Yes, it is possible to 3d print wax, but there are not any inexpensive printers that can do it as best I know (but I likely don't know best!). The problem would be finding the wax in the form of a filament that would stand up to the feeding.

However, apparently many folks have 3d printed forms in PLA, then melted the PLA out in the oven. I haven't tried it myself ...

On edit: I see that other posters got there before me. Sorry for the repeat info!

Have you checked the usual suspects in England to see if suitable castings already exist. Not sure if your proposed model is a Sentinal or other but a little networking may find a source already exists. Reeves, Blackgates, LivesteamModels, etc.

I look forward to following your project.

Lucky7

Word of caution: Converting PLA to cast iron is conceptually simple. Casting iron is conceptually very simple. Talk to guys who are doing it. Actually figuring out what is needed to make a usable casting is not simple. Just like many aspects of machining are conceptually simple. You know---put 304SS part in 6x19 “import” lathe, use crappy 3-jaw, spin it, cut threads and fancy features. Hold .0001 tolerances and do it fast. Simple right? Yes, 304 can and is machined every day, but it ain't 12L14.

I am aware of a couple of folks who are working to break new cast iron ground trying to use burnout PLA on a small basis. I am unaware of anyone who has had success molding cast iron parts with it to date. I expect they will get it figured out eventually. There are also folks making simple lost foam parts with iron. I saw my first reported success a few days ago.

Denis

I agree with Oldwrench
8mm is no problem in CI
Use eighter furan or urethane binder which will cool the casting not as fast as green sand
Perhaps pour the wheel standing up so you have a smaller rizing surface which cools slower
I did have amazing results with that technique


Peter

dgfoster said:

About 18 months ago I began the process of setting up an iron foundry to cast relatively thin cast iron patterns for sale as straight edges. You should and maybe do know that casting iron is much more difficult than casting brass/bronze/ aluminum.

Click to expand...

Absolutly untrue in my humble experience Especialy if you look at it from a metalurgic point of view
Cast iron is the easiest Even getting the right temperature is not that hard
If you use a crucible oven the CI will upgrade in quality even

Peter

A suggestion regarding your patterns: unless you are already a woodworker and plan to make patternmaking your principal hobby rather than machining and assembling the steam engine, you might be better off (and save a lot of time if not money) by modeling your parts with the draft necessary for casting (can't tell from the pics whether that's on the drawings) and having them 3D printed in ABS (weedwacker-string method). That is generally the least expensive although your parts are fairly large. You can cut that cost by modeling your part as a shell about .100 thick with the inside a supporting mesh. That will withstand hand ramming if they are aware of it in advance. You will have to use Bondo to get rid of the log-cabin layering on vertical surfaces.

An experienced molder can use a loose pattern, meaning it doesn't have to go on a match plate. Try to befriend a local expert. Good luck.

“
Absolutly untrue in my humble experience Especialy if you look at it from a metalurgic point of view
Cast iron is the easiest Even getting the right temperature is not that hard
If you use a crucible oven the CI will upgrade in quality even “

Peter,

Can you tell us what hands-on experience you have cuz I am puzzled and amazed by this assertion. It is contrary to my experience and the experience of everyone I know in casting whether commercial or backyard.

A few phots of your setup and castings would be great.

Denis

To the OP, I've tried blowing up your drawings without success in seeing what type of wagon you'd like to make. Sentinal? Aveling and Porter? Other?

L7

Sand casting problems with ramming up image???
Post 18 have some examples

Here is a post about my oven )without pictures I see I will ad these if I can find them Crucible oven for cast iron

nice write up Peter, I hope you find the photos. Do you worry at all about the mold temperature or just pour away? Your castings come out nice and machinable generally, without hard chill spots etc?

I think I also always assumed CI was a challenge, maybe just because you need an oil burner for the higher temperatures

Peter from Holland said:

Sand casting problems with ramming up image???
Post 18 have some examples

Here is a post about my oven )without pictures I see I will ad these if I can find them Crucible oven for cast iron

Click to expand...

Peter,

Those are some nice castings. The little cast iron flywheel is quite delicate an nicely done. The bronze blower or pump housing is excellent.

If you found cast iron easy, my hat is off to you because that is hardly the common experience. Here is an interesting
post and thread in AlloyAvenue that reviews one person's quest in the pursuit of casting iron. I particularly related to his comment that he made a successful casting and thought he 'had it made" opnly to fail miserably on his next attempt. Cast iron reportedly has a universal humbling effect that I can also vouch for. I am now on about melt number 200 averaging 40 to 50 pounds per melt for about 4 4 or five tons of iron melted. I am still getting my chain jerked by cast iron just when I think I have it all figured out.

The Bitch that is Cast Iron...

There are endless similar accounts in Alloy Avenue and TheHomeFoundry.

So, the OP may find casting iron to be the simplest metal to cast should he be quite lucky and capable. I hope he does. But, if he is like most people who go down this path, he should be prepared for setbacks, disappointment, and at times near despair as most people report those experiences when setting up their iron foundry and getting it running.

Denis

I started out with bronze So all the foundry problems I had covered already when I started with CI You have to account for that
I then was at a point where at least the second casting was succesfull
The bronze pump was good at its second attempt Pictured is the first attempt The core shifted a bit and made a small hole which I soldered
First picture in that link shows my prefered methode The flasks standing up On many parts your rizing surface is much smaller that way The CI wheel I attemted 7 or 8 times laying down Everytime with a better sprue design But never succesfull With the flask standing up I then never had a failure anymore I did cast a lott of these
Seldom had hard castings With a crucible oven you best use a poor quality CI because a crucible upgrades the CI significantly. I used a lot of counterweights for windows Use big chunks of CI to melt Not small scrap

Peter

I have been supplying 1/8 scale locomotive castings for the past 30 years and thin sections aren't really a problem. If you have some castings that are hard you can put them in a oven and take the temperature up to 1750 -1800 degrees and control the cool down temperature to anneal the castings.

Hi
Thanks for all the info.

I want to build a Yorkshire Patent Steam Wagon. I have copies of the factory drawings for wagon number 1535 that was imported into New Zealand August 1925. There is a link to the full size wagon in the first post. No known castings exist for what I want to do.

I figure that it will be easier to make a 1/3 scale wagon than something smaller. A miniature of that scale will be small enough to machine with the tools I have.

I would much prefer to cast in sand based molds rather than lost wax. It requires a lot less equipment and it's a lot cheaper. Also investment slurry and waxes are simply not available here. I would have to import them at great expense.

The other big advantage with sand is that the pattern remains intact and reusable after the inevitable cast failures. I can't buy casting sand here but I can make up casting sand with local ingredients.

I don't know anyone that does there own castings here. I am sure they exist but I don't know them.

I found Polycast, a filament especially made for 3D printing patterns that are then burnt out.

The drawings posted here are limited by the file size I can post here. The original images are much higher quality. The blue plastic has a 4 inch circle inscribed. This gives me an accurate reference to scale the photographs.

I won't be starting making anything for at least a year. The factory drawings list over 60 patterns. I can start with the simpler patterns and work up to the more complex ones. The flywheel, for example, is very plain and would be easier to machine than cast.

If I can sand cast most items, it would probably be cheaper/easier to have the remaining complex castings done professionally.

I am still concerned about the thinness of the scaled castings. Some of the full size castings are only 5/16inch thick. I can make the castings a little thicker than scale but there are limits without causing cascading side effects.