Why get into foundry?

What live steam modeler hasn't dreamed of making his own foundry rough ? It is exactly this meaning that pushed me to start on the adventure... Because it is indeed an adventure made up of a succession of failures before getting the desired result. It took me almost 6 months to get my first really usable part after testing various molding process. As of this writing, all of my parts have been cast in bronze (CuSn12) made from scrap copper and tin.

These pages will describe the foundry process that I have chosen to make mechanical parts in bronze from the building of equipment such as the melting furnace, the burner, the making of the molds, the development of the alloy, and much more. And of course the casting.

My final goal is the production of rough castings for the building of a french Merlin 12A type locomotive on a 1/10th scale.

This presentation page is intended to show the main lines of the technique that I use. The process will be detailed in more technical articles for each step.
The "foundry" pages are still being written, come back regularly.


Foundry is a dangerous hobby and it is imperative to know the risks and safety rules before starting.
I can in no way be held responsible for any injuries caused, however serious they may be.

The basic rules :
Mandatory wearing of appropriate safety equipment, goggles, high temperature gloves, high temperature clothing, safety shoes and leather gaiters.
Never immerse tools or non-preheated metals in liquid metal, the presence of humidity can cause a steam explosion and cause splashes of molten metal, or even the explosion of the oven.
Never pour metal into a wet mould, there too there is a risk of steam explosion and therefore of explosion of the mould.

Always work in a very well ventilated room because the combustion of propane at high power generates carbon monoxide which is a heavy and deadly gas, in a closed room it will accumulate on the ground and attack you.

Failure to follow these few basic rules can quickly lead you to the emergencies with very serious burns.

Some examples of bronze castings

To make you want to get started, here are some parts cast in bronze (CuSn12) with the lost PLA technique, molds made with a mixture of plaster of Paris, sand and fiberglass. This technique will be described later in these pages.
Some trinkets made from 3D models downloaded on Thingiverse and printed in PLA with my Ender 3 V2.

At the bottom of the photo, a first set of parts of the Merlin 12A locomotive at 1/10th scale, it is the fireplace door and its frame.

When I cast these parts, several months of development had already passed, marked by numerous failures. Do not be discouraged because the learning curve can be long.
Here we change the level of difficulty, these are the first pieces for the Merlin 12A locomotive. In the center, the engine frame with still many defects, this part will not be usable. On each side, the flying wheels which came out perfect on the first casting. At the bottom right, the cylinder and the steam box, there also good on the first casting, the same at the bottom left with the slide guides.
The engine frame is clearly at the limit of feasibility with my method, the cluster weighs around 1kg200 and the thinnest thicknesses are below 3mm...
Home made bronze casting gallery
Ready to start on the adventure...
So may the force be with you...
See more
A Youtube channel with lots of top casting, not to be missed
Youtube chanel
My Youtube chanel with some technics videos.
See more
Youtube chanel with many diy castings

The foundry and the work shop

The tools that will make up your foundry is very important and must either be bought commercially or homemade. As usual, I chose to make everything from what can be found in large DIY stores, except of course the crucibles which are purchased (Amazon) it is also a question of safety because it does not must never forget that molten bronze is around 1200°C, a crucible that breaks is not an option.
The melting equipment with of course the crucible furnace but also other essentials: the ingot molds, the tongs to take out the crucible and pour, various tools for gripping the lingot molds, cleaning the molten metal, grabbing the metal to be melted.
The furnace is powered by propane gas. This furnace can melt 1kg200 of bronze in less than 30 minutes.
Depending on the foundry process used, a second furnace may be useful to bake the molds. I use the lost PLA process which requires baking the molds at around 700°C to completely eliminate the model printed in PLA and baking the mold.
This furnace is rectangular with a propane burner in the lower part which heats a sole, the flame is not in direct contact with the mould.
See more
A Youtube channel with lots of top casting, not to be missed.
Homemade furnace.
See more
Youtube chanel with many diy castings
Homemade furnace

The base metal

Many metals and alloys can be cast, but for an hobbyist it is important to know which alloy is used, which excludes to take scrap from anything and everything at the risk of not mastering anything.
For the coppery ones, we have the choice between bronzes and brasses, even some exotic ones like Nordic gold. The basic components such as copper, zinc and tin are relatively easy to find and it is therefore possible to develop your own alloys.
For aluminum alloys, it is more delicate because only recovery is possible and there it is much more delicate because all aluminum alloys cannot be used correctly in foundries, it is therefore only necessary to recover parts which have was made in a foundry. Contrary to what we see on the web, you should not use cans or aluminum profiles that are not foundry alloys.
Pure copper
If like me you want to make your alloys, you have to start by making ingots with various scraped metals.
To begin with, copper which is the main component of bronze and brass. You can recover some with plumbing pipes, electrical wire from old trinkets...
Be careful to take real copper and not close alloys because the results would not be up to par. The melting point of copper is 1080°C, and it is cast at 1200°C.
Another source of scrap, foundry parts in aluminum alloy. It is imperative to recover foundry parts in order to have the right alloy because, unlike copper, making your own alloy by mixing the components is not possible because you cannot find pure aluminum in recovery. The ingots in the picture come from an electric motor frame, so it is an AS10 or an AS13 well suited to foundry.
Aluminium alloy like AS10
For the other base metals, you will need zinc which is easy to find with old rain gutters, but be careful when melting zinc gives off toxic vapours, do not expose yourself to fumes.
Another essential metal for the production of bronze is of course tin, which can be found in old trinkets but also from zinc welding rods, be careful to buy rods whose composition is indicated and which are very rich in tin, I take ROTHENBERGER which are Sn91Zn9 so only 9% zinc which will not interfere with your bronzes.
See more
bigstackD Casting
Youtube channel with lots of sources of scrap, but be careful it often only make lingots...
See more
BigstackD casting
Youtube chanel with many metal scrapping sources.

Make your bronze, and other alloys

If you want to control the quality of your alloy, it is best to make it yourself. For bronze it's very easy, just melt copper and tin together...
Yes, but not in any proportion.
Bronze is composed mainly of copper with between 5 and 25% tin. For the mechanical parts we will use 8 to 15% tin, for the bells we need between 20 and 25%.
The more tin the better the flow, but too much tin reduces the mechanical characteristics and increases the fragility, on the other hand the sound is better for the bells.
For my parts, I chose to use 12% tin, in other words it is CuSn12 bronze.
Important point, the percentages are relative to the masses of each component, so easy to dose with a simple kitchen scale.
Ready to start melting
To prepare a casting charge, I put in my cold crucible, lingots or scrap bronze from my previous castings and new metal.
I usually also add a rod of copper phosphorus solder (plumbing solder) because adding a very small amount of phosphorus improves the flowability a bit.
If you want to develop other foundry alloys, brass for example, you have to alloy copper with zinc, there it is possible to put a lot more zinc, up to almost 40%.

Another interesting alloy but of medium flowability is "Nordic gold", as its name suggests it looks like gold with a bright yellow appearance, but of course worthless. It is an alloy with 89% copper, 5% aluminum, 5% zinc and 1% tin.
Nordic gold
See more
Presentation of industrial copper alloys (french).
See more
Presentation of copper alloys (french).

Model and mold

Several methods are possible for the mold making, and the manufacture of the model will depend on the choice of the type of mold.
We will not talk about permanent steel molds which are not within the reach of hobbyist and are reserved for large industrial series.

We are going to make lost molds, they are only used for one casting. To make them, several solutions are possible:

1- Green sand or oil sand molds
2- Chimical sintering mold
3- Lost PLA molds
Green sand mold and model
Green sand molds (or oil sand molds) which will be made by pressing foundry sand onto a model and then removing the model to leave the cavity of the part. A greensand mold retains residual moisture that keeps the sand in place without being dangerous with liquid metal.

The models can be made manually, machined or even simpler printed in 3D, it is this last solution that I chose.

It is easy to make green sand by mixing fine sand (grains <0.5mm) with clay (bentonite). Sand can be found in large DIY stores, and clay too... in the animal department because the cat litter is perfect.
Sand molds with chemical binder can remain within the reach of the homemade if soda silicate is used as a binder.
The mold or core is made with a mixture of fine sand and soda silicate, before unmolding the mold must be gassed with CO2 to cause hardening.
Soda silicate can be bought on the web or it is still possible to make it yourself, but be careful because handling hot soda is dangerous.

The model or the core box can advantageously be printed in 3D.
Sand silicat core and core box
Lost PLA mold and model
The most suitable technique for complex parts is that of lost PLA, which in fact is only a variant of the lost wax commonly used in industrial foundry and art foundry.

We print a model and its entire casting system in PLA with parameters that use as little PLA as possible because it will have to be eliminated before casting by burning the mold at high temperature.

A shell is then deposited all around the model to form the mold. This shell is made with a mixture of plaster of Paris (1 volume), fine sand (1 volume) and water (1 volume), add small strands of fiberglass and during the manufacture of the mold, it is necessary reinforce with fiberglass braids.
To learn more about foundry sands, you can check out my article on making homemade greensand and oil sand by following this link.
See more
Water glass
How to make water glass, witch is soda silicate
DIY sand
Carnets JLS page about homemade casting sands
See more
Water glass
How to make water glass
DIY sand
Carnets JLS page about casting sands DIY

Burning mold and casting

This article quickly shows the casting process from the burning of the mold to the cold part just after braking the mold. Each step will be the subject of a more detailed description with the burning cycles, the preparation of the melting metal, and the easy mold breakage.
Mould burning
All my lost PLA molds dry naturally for a week minimum.

On the day of casting, the mold is gradually heated in order to dry it out, but above all to completely eliminate the PLA by burning it. This burning lasts between 1 and 2 hours depending on the mould.

The burning of PLA is done in an open oven to properly burn the gases generated by the PLA.
Once the PLA burnt, we no longer see any flames, the final rise in temperature is done in the closed oven.

The mold is ready for casting when the upper part has reached 650°C.

Depending on the complexity of the part, you must either cast it in a very hot mould, or let it cool down a little, which in this case facilitates the solidification of the bronze.
No more PLA
The metal is ready for casting
During the firing of the mould, hence the importance of having two ovens, the metal is prepared and heat up to the casting temperature of 1200°C.

The melting metal is made up of offcuts from previous castings, new metal (copper and tin), phosphorus additive (welding rods) and cleaned with a special copper flux.

The temperature can be controlled with a thermocouple probe, or with practice simply by eye by controlling the color and the fluidity of the bath.
The fastest operation of the whole process is the casting itself, the filling of the mold must be very regular, trying to draw as little air as possible into the mould.

It is very important never to stop pouring the metal until completely filled the mold, otherwise there will be defects on the part.

Once casting is complete, generally less than 30 seconds, the mold must not be moved until the surface of the metal has cooled to less than 500°C.
Casting is done
The part just after braking mould
And here is the end result... when all goes well.

A beautiful part out of its mold with still the sprues and the vents.

The good design of sprues, vents and of course the part itself is done with experience. Each casting failure is very rich in lessons, it is necessary to observe the part and its defects to understand what happens when the metal is still liquid in the mold.
I hope this presentation page has given you the desire to make your own experiences. I am at your disposal to give you the necessary information on my process, for this go to the contact page.
Creatif Pro
Site selling fluxes and other foundry products (french).
Creatif Pro
fluxes and foundry products
Made with OpenElement
Last update
Technical hobbies
Carnets JLS
Top page