Sand Casting vs. Investment Casting

The short answer first: the choice comes down to four things — how tight your tolerance and surface finish need to be, how big and complex the part is, your volume, and your budget. Sand casting wins on size and low tooling cost. Investment casting wins on precision, surface finish and intricate geometry. Everything below is just the detail behind that.

Both are pouring molten metal into a mould — the difference is the mould. That single difference drives every number in this guide.

How sand casting works — and what it's good at

A pattern is packed in sand to form a single-use mould; metal is poured, cooled, then the sand is broken away. Because the mould is sand, it's cheap to make and can be enormous — but the surface carries the sand's grain texture and the tolerances are looser.

• Tolerance: CT10–CT13 (ISO 8062) — typically ±0.5–1.5 mm.
• As-cast surface: Ra 12.5–50 µm (rough; mating faces usually need machining).
• Minimum wall thickness: about 3–5 mm.
• Size: effectively no upper limit — from under a kilogram to several tonnes.
• Materials: almost any castable metal — grey and ductile iron, carbon and alloy steel, aluminium, bronze.

Typical parts & industries: large machine bases and housings, pump and valve bodies, engine blocks and gearbox cases, agricultural and construction equipment parts, counterweights, manhole covers. See our sand casting service.

How investment casting works — and what it's good at

A wax pattern is coated in a ceramic shell; the wax is melted out ("lost wax"), and metal is poured into the hard shell. The rigid ceramic mould captures fine detail and delivers a near-net-shape part — often needing little or no machining on non-mating surfaces.

• Tolerance: CT4–CT7 — typically ±0.1–0.3 mm (roughly ±0.005″ per inch).
• As-cast surface: Ra 1.6–6.3 µm (smooth; often the finished surface as-is).
• Minimum wall thickness: down to about 1.5–2 mm, with intricate detail.
• Size: best for small-to-medium parts; most shops top out around 50–70 kg (100–150 lb).
• Materials: very wide — including stainless, tool steel, and nickel/cobalt superalloys hard to machine.

Typical parts & industries: turbine and pump impellers/blades, valve trim, medical and dental components, firearms parts, aerospace brackets, precision hardware and fittings. See our investment casting service.

Head-to-head: the numbers that decide it

Notice the pattern: sand casting shifts cost to post-machining (rough surface, loose tolerance), while investment casting shifts cost to tooling (precise, smooth as-cast). Which is cheaper for you depends on how much finishing your part would need either way.

A quick decision guide

Frequently asked

What tolerance can investment casting hold?

Typically CT4–CT7 under ISO 8062 — around ±0.1–0.3 mm on precision castings (roughly ±0.005″ per inch). Sand casting is generally CT10–CT13, about ±0.5–1.5 mm. Where a mating dimension needs to be tighter than the as-cast grade, we machine that feature after casting.

How heavy can a sand casting be?

There is no practical upper limit. Sand castings run from under a kilogram to several tonnes; parts over 3 tonnes are routine in the industry. Tell us your part weight and envelope and we'll confirm feasibility for your specific alloy.

What is the smallest, most intricate part investment casting can make?

Investment casting is built for small, complex parts — down to a few grams, with walls as thin as ~1.5 mm and fine detail (thin blades, undercuts, lettering) that sand casting simply can't hold.

What surface treatments are common on cast parts?

Standard cleanup is shot or sand blasting, plus machining of mating faces. Beyond that: painting, powder coating, plating/galvanising, anodising (aluminium), and passivation for stainless. Investment castings usually need less finishing thanks to their smoother as-cast surface.