Custom Cast Iron Castings & Parts: Gray & Ductile Iron, Poured to Your Spec

One Off Castings pours custom cast iron parts—both gray iron and ductile iron—to the grade and geometry you specify, with no minimum order. You (or your engineer) supply the drawing, CAD model, or a physical sample plus the ASTM grade you require; we reverse-engineer the geometry when needed and pour to that spec. It is the fast route to a single custom iron casting, a short run of replacement parts, or a low-volume production batch, without paying for permanent hard tooling.

What "custom cast iron" means here

A custom cast iron casting is an iron part made to your requirements rather than pulled from a catalog: a discontinued gearbox housing, a bespoke machine base, a replacement pump or valve body, or a prototype bracket that will never enter mass production. One Off Castings is a short-run foundry built specifically for this work. We are a division of Southern Cast Products, and our entire operation in Jonesboro, Arkansas is organized around one-off and low-volume castings—not around squeezing your single part into a high-volume production schedule.

Because we build molds digitally with patternless 3D sand printing and robotic mold-making (robocasting), there is no pattern to commission, store, or repair. That removes the biggest cost and lead-time barrier that normally makes a custom iron part in quantities of one to fifty uneconomical.

The cast iron grades we pour

You specify the grade; we pour to it. Cast iron is not a single material—the ASTM designation you or your engineer calls out determines the microstructure and mechanical behavior of the finished part. These are the iron alloys we commonly pour:

Gray iron

Gray iron takes its name from the flake graphite in its microstructure. One Off Castings pours gray iron to:

• ASTM A48 — Class 25, 30, 35, and 40 (A or B). In the A48 system the class number is the minimum tensile strength in ksi, so Class 30 denotes a 30 ksi minimum and Class 40 a 40 ksi minimum.
• ASTM A278 — Class 25, 30, 35, and 40 (A or B), for pressure-containing parts.
• ASTM A436 — Grade N1B (austenitic "Ni-Resist" gray iron).

Ductile iron

Ductile iron (also called nodular or SG iron) uses spheroidal graphite, which gives it meaningfully higher strength and elongation than gray iron. We pour ductile iron to:

• ASTM A536 — grades 60-40-18, 65-45-12, 80-55-06, and 100-70-03. The three numbers encode minimum tensile strength (ksi), minimum yield strength (ksi), and minimum elongation (%): grade 65-45-12 is 65 ksi tensile / 45 ksi yield / 12% elongation.
• ASTM A439 — Grade D2 (austenitic ductile iron).

We do not tell you which grade to use—that call belongs to your engineer, who owns the design intent and the service conditions. If you supply a worn or broken sample without documentation, we can reverse-engineer the geometry and pour to the grade you specify.

Gray iron vs. ductile iron, briefly

The two families behave differently because of graphite shape, and the difference matters when your engineer writes the spec. Flake graphite in gray iron gives excellent damping, machinability, and thermal conductivity, which is why it is common in bases, housings, and enclosures. Spheroidal graphite in ductile iron interrupts crack propagation far less, so ductile iron carries higher tensile strength and real elongation—useful where a part sees shock or tensile load. This is descriptive context, not a recommendation: the appropriate grade for your part is the one your engineering specification calls out.

Beyond iron: one foundry, one point of contact

Many custom iron projects also involve a companion part in steel or aluminum. One Off Castings pours a broad ferrous and non-ferrous range in-house—carbon and low-alloy steel (ASTM A216 WCB/WCA/WCC, A352 LCB), stainless (ASTM A351, A743, A744, A890, A995), and aluminum (ASTM B26 alloys 319, A356, C355) with in-house aluminum heat treat—so a multi-material job stays with one supplier and one point of contact.

Why buyers choose One Off Castings for custom iron parts

• No minimum order. One part is a real order here—single castings, small replacement runs, and low-volume production are the core business.
• No pattern required. Patternless 3D sand printing and robocasting build molds directly from your CAD or from a reverse-engineered sample, so there is no hard-tooling cost or storage.
• Reverse engineering from a sample. No drawings? Send the worn part. We capture the geometry and pour a replacement to your specified grade.
• Simulate before we pour. In-house casting simulation (MAGMA/NovaCast) helps us verify filling and solidification before committing metal.
• U.S.-based, engineer-led. Poured in Jonesboro, AR, with direct access to technical staff.

Frequently asked questions

Can I order just one custom cast iron part?

Yes. There is no minimum order. One Off Castings is built for single castings and short runs, so a quantity of one is a standard order, not an exception.

What cast iron grades can you pour?

Gray iron to ASTM A48 (Class 25/30/35/40), A278, and A436 (N1B); ductile iron to ASTM A536 (60-40-18, 65-45-12, 80-55-06, 100-70-03) and A439 (D2). If you need a grade not listed, contact us and we'll confirm what's possible.

Do you choose the iron grade for me?

No. Alloy and grade selection is your engineer's responsibility, based on the part's design intent and service conditions. You specify the grade—or supply a sample plus the spec—and we pour to it.

I don't have drawings for an obsolete iron part. Can you still make it?

Yes. Send the existing or broken part. We reverse-engineer the geometry into a digital model and pour a new casting to the grade you specify—no original pattern or drawing required.

Where are the castings poured?

In Jonesboro, Arkansas. One Off Castings is a division of Southern Cast Products, serving engineers, buyers, and maintenance teams across the United States.