Before acquiring my home foundry, I spent many years watching other hobbyists and machinists make patterns, cast parts, and solve engineering problems by producing their own metal components. The ability to create a needed part from raw metal seemed almost magical. Today, affordable tools, readily available information, and small electric furnaces have made metal casting accessible to hobbyists working in home workshops.
\section{Pattern Making}
Every casting begins with a pattern. The pattern is a physical model of the desired part and is used to create the cavity in the mold that will later be filled with molten metal. Patterns can be made from wood, plastic, metal, or foam. One of the enjoyable aspects of foundry work is that it combines many different skills, including woodworking, machining, fabrication, and drafting. \index{pattern}
In recent years I have found that three-dimensional printing is one of the easiest methods of producing patterns. A pattern can be designed in CAD software, printed on a desktop 3D printer, sanded smooth, painted, and then used directly in the molding process. \index{printing, 3D} \index{pattern!printed}
Some castings require internal cavities or passages that cannot be formed by the pattern alone. In these cases, a core is used to create the negative space within the mold. Cores are typically made from sand mixed with a binder and are placed inside the mold before pouring. \index{pattern|core}
Small fillets and radii can be added to a pattern using wax, automotive body filler, or similar materials. These features improve mold filling and reduce stress concentrations in the finished casting. \index{fillets}
Depending on the molding process, surprisingly fine details can be reproduced in a casting. Surface textures, layer lines from 3D-printed patterns, engraved lettering, and small geometric features may all appear in the finished part.
\section{Lost Foam Casting}
For one-off projects and prototype work, a pattern may be constructed from polystyrene foam that has been cut, shaped, and glued together. The foam pattern is coated with a refractory slurry and allowed to dry. The coated pattern is then buried in loose sand without the use of a conventional mold. \index{lost foam}
During pouring, the molten metal vaporizes the foam and occupies the space previously filled by the pattern. This process is known as lost foam casting. While the method is simple and requires minimal tooling, it produces significant smoke and generally yields a rougher surface finish than conventional sand casting.
\section{Casting Shrinkage}
The pattern should have the same general shape as the finished part, but it must usually be made slightly larger to compensate for metal shrinkage during solidification and cooling. As the casting cools from the pouring temperature to room temperature, its dimensions decrease. \index{shrinkage allowance}
For many aluminum castings, a shrinkage allowance of approximately 1/8 inch per foot of length is adequate. Commercial foundries often use shrink rules or calculate shrinkage allowances based on the alloy being cast.
In my own projects, dimensional tolerances have rarely been critical, and shrinkage has not significantly affected the usefulness of the finished parts. However, shrinkage should always be considered when producing castings that must fit existing components or meet specific dimensional requirements.
\section{Casting Ingots}
Before you can cast parts, you will need a supply of metal. Suitable sources of aluminum include discarded lawn mower engines, vacuum pump housings, cookware, transmission housings, and other cast aluminum components. In general, if a part was originally produced by casting, it will often provide a suitable alloy for future casting projects. \index{aluminum!ingots}
New casters are frequently tempted to melt aluminum beverage cans and other thin packaging materials. While this can be done, it is generally inefficient. Because the material is thin and has a large surface area, much of the aluminum is lost to oxidation during melting. Large quantities of cans are required to produce a relatively small amount of usable metal. \index{aluminum!beverage cans}
I prefer to process dirty, oily, painted, or otherwise contaminated scrap in my propane furnace. After the metal has melted and impurities have been removed, the clean aluminum is poured into ingot molds for storage and future use. I commonly use a cast-iron muffin pan to produce small ingots and a steel angle-iron mold to produce triangular-section ingots. \index{ingot mold}
These clean ingots become the feedstock for my electric resistance furnace. By charging the electric furnace with previously processed metal, I reduce contamination, minimize smoke and fumes, and improve the overall casting experience. In practice, the propane furnace serves as a metal-processing furnace, while the electric resistance furnace serves as a clean melting and casting furnace.
\section{Mill Pendant and Wrench Hanger}
While working in the machine shop, I identified a need for a hanger to hold the milling machine control pendant and the vise wrench. I designed the required part in Onshape and produced the first version using a desktop 3D printer and polylactic acid (PLA) filament. \index{PLA filament}
The plastic part performed well in service for a period of time, but it was eventually damaged and broken. Rather than printing another plastic replacement, I decided to use the design as the basis for a permanent metal part.
A second PLA model was printed and used as the pattern for a sand casting. The pattern was rammed up in oil-bonded sand, removed from the mold, and replaced by molten aluminum. After the casting had cooled, it was removed from the mold, the sprue was cut off, the back surface was sanded flat, and the mounting holes were drilled to final size.
The finished aluminum hanger is considerably stronger than the original plastic version and has proven to be well suited for shop use. I expect the machine shop will continue using this part for many years.
\section{Metal Carbide Part Core}
Another opportunity to apply metal casting arose at work during an experiment involving the ramming of metal carbide powder into a mold that combined features from two separate parts. I believed the design could be improved by incorporating an aluminum core with rounded corners. The rounded edges would form fillets in the compacted powder part, reducing stress concentrations and improving the likelihood of successful processing. \index{fillets}
The core was designed in CAD and printed on a 3D printer using polylactic acid (PLA) filament. Because of its large size, the pattern was printed with only 5\% infill to reduce material consumption and printing time. Care was taken to provide sufficient draft so the core could be easily removed from the molded carbide part. After printing, the pattern was sanded smooth and coated with several layers of filling primer. \index{PLA filament} \index{draft}
The core was cast in an oil-bonded sand mold and required approximately 12 kilograms of aluminum, making it the largest casting I had produced at that time. After cooling, the casting was removed from the mold, the sprue was cut off, and it was finished by sanding and smoothing the surfaces.
The casting contained several surface pits and voids that were not intended. I suspect these defects were caused by entrapped air, turbulence during pouring, or sand inclusions in the mold. Large castings may require a riser, which is a reservoir of molten metal connected to the casting. As the casting cools and shrinks, the riser supplies additional metal to compensate for solidification shrinkage and reduce the formation of internal voids.
Although the casting was not cosmetically perfect, it was fully functional for its intended purpose. \index{casting defects}
The completed core was taken to work and used in the production experiment. This project demonstrated how a home foundry can be used to rapidly produce specialized tooling and fixtures that would otherwise be difficult or expensive to obtain.
\section{Cast Parts for Furnace Mast Support}
During the construction of the furnace described in this book, I needed specialized brackets to attach the lid-lifting mast to both the furnace body and the removable lid. Commercial hardware such as antenna mounting brackets was considered, but the available parts did not fit the application particularly well. Because a home foundry was available, designing and casting custom components became a practical alternative.
The brackets were designed in Onshape and the patterns were produced using a 3D printer and polylactic acid (PLA) filament. The patterns were rammed up in oil-bonded sand molds and cast in aluminum. \index{PLA filament} \index{OnShape}
After cooling, the castings were removed from the molds, the sprues were cut away, and the surfaces were sanded smooth. The mounting holes were then drilled to final size and the parts were painted with high-temperature black paint.
The finished brackets were used to attach the mast assembly to the furnace. This project illustrates one of the greatest advantages of having a home foundry: when a specialized component is needed, it is often possible to design and manufacture the part rather than search for a commercial substitute.
\section{Shop-Built Foundry Tools}
As my foundry activities expanded, I accumulated crucibles of various sizes and discovered the need for specialized handling equipment. Commercial foundry tools are available, but they can be expensive and are not always suited to a particular crucible size. As a result, I fabricated my own lifting tongs and pouring shanks from rectangular and round steel stock, assembling the tools by welding. \index{tongs}
Additional molding flasks were constructed as needed from dimensional lumber and common hardware. Building these flasks allowed me to produce larger castings without purchasing commercial foundry equipment. \index{molding!flasks}
Like David Gingery before me, I learned to repurpose ordinary items for foundry service. Slotted spoons purchased from a thrift store became skimmers for removing dross from molten metal. A flour sifter was adapted for screening molding sand. Cast-iron cookware found new life as ingot molds. \index{ingot mold} \index{sand riddle} \index{Gingery, David}
One of the lessons learned from building a home foundry is that the furnace itself is only the beginning. As new projects arise, additional tools, fixtures, molds, and handling equipment are often needed. Many of these items can be fabricated in the home workshop, further expanding the capabilities of the foundry and the skills of its operator.
\section{Lessons Learned}
\textbf{Most castings succeed on the second or third attempt} rather than the first. Defects such as misruns, shrinkage cavities, gas porosity, and sand inclusions are common, particularly when learning a new process. Success comes from carefully observing the results, changing one variable at a time, and persistently refining the mold and pouring technique. If you are willing to learn from your mistakes, each failed casting becomes a valuable lesson. \index{casting defects}
\textbf{Draft and fillets matter.} Without adequate draft, removing the pattern from the mold can be difficult and may damage the mold cavity. Fillets improve mold filling, reduce stress concentrations, and make patterns easier to withdraw from the sand. These features should be considered from the earliest stages of the design process. \index{draft} \index{fillets}
\textbf{Pattern quality directly affects casting quality.} Casting processes are capable of reproducing surprisingly fine details, including surface textures, tool marks, and layer lines from 3D-printed patterns. Time spent improving the pattern will generally be rewarded with better surface finish, more accurate castings, and fewer molding problems.
\textbf{A home foundry provides a level of independence} that is difficult to achieve by other means. Instead of searching for a commercial solution, the foundry operator can often design and manufacture a custom part, tool, or fixture as needed. The ability to transform an idea into a functional object is both practical and deeply satisfying.
\section{\;\,In Closing}
The project described in this book provides more than a means of melting metal. Along the way, the builder gains experience in design, fabrication, electrical wiring, temperature control, refractory construction, and furnace operation. These skills can be applied to countless future projects and often prove to be as valuable as the castings themselves.
At the conclusion of the project, the builder is left with something equally valuable: a practical tool capable of supporting future work in metal casting, heat treatment, materials experimentation, and shop fabrication. The furnace is not the end of the journey, but rather the beginning of a new set of possibilities.
Whether the next project is a replacement machine part, a custom tool, an artistic casting, or an entirely new machine, the furnace provides the capability to transform ideas into physical objects. In that sense, the greatest value of the project is not the furnace itself, but the opportunities it creates.
If you have questions, comments, suggestions, or would simply like to share your own experiences, please feel free to contact me at vincethigpen@yahoo.com. I try to check my email regularly and would enjoy hearing about your personal metal casting journey.
Thank you for reading this book, and best wishes for success in your future projects.
