Process Deep-Dive · 3D-Printed Sand Molds
1906 Moline cylinder jug
A cylinder jug for a 1906 two-cylinder Moline engine — 40 lb of gray iron, modelled in 3D CAD from two originals, one of them already destroyed and available to section.
The process, step by step
Reading the part from two originals
A jug is mostly hollow, and the hollow is what has to be modelled. An intact original gives the outside only. A destroyed jug came with the good one and could be cut up, which put the internal geometry within reach of a caliper.
Start with what survived
The good original, on the bench with a rule across it. Every external dimension comes off this part — but a jug is a water jacket wrapped around two bores, and none of that is visible from outside.
The destroyed jug, sectioned
Opened up, the jacket, valve pockets and wall thicknesses can be measured directly rather than inferred.
Wall thickness, read from a fragment
A piece of the broken jug in section. Wall thickness drives solidification: get it wrong and the part either misruns or shrinks into itself.
Measured, then modelled
A straightedge across the valve pockets. The original was made from a hand-carved pattern and was never drawn, so the model follows the shape as found rather than regularising it.
Out of the mold, still orange
The jug at shakeout, printed sand broken away around it.
The raw casting, cleaned
Gate and risers off, ready to go to the customer for machining.
From the valve side
The ports and bosses as cast — no weld repair, no filler.
Material
Gray iron, to ASTM A48
Gray iron to ASTM A48, certified to the same chemistry tolerances we hold for industrial production. Gray iron suits a part like this: it is fluid enough to render fine as-cast detail and it damps vibration in a way steel does not.
| Grade | Min. tensile (psi) | Hardness (HB) | Typical use |
|---|---|---|---|
| Class 20 | 20,000 | 141 (max) | Intricate, low-stress castings |
| Class 25 | 25,000 | 174 | General-purpose work |
| Class 30 | 30,000 | 201 | Engine blocks, housings |
| Class 35 | 35,000 | 212 | Higher-strength service |
| Class 40 | 40,000 | 235 | Heavy-duty, wear-resistant |
Where a part needs steel-like ductility instead, we cast ductile iron to ASTM A536 (60-40-18 through 100-70-03). Every heat is verified by tensile and Brinell hardness testing in house.
Where the difficulty is
- Thin walls — jacket sections are near the lower limit for filling gray iron, and wall thickness governs how the part solidifies.
- Delicate cores — the jacket core is slender and largely unsupported, and sets the wall thickness it is surrounded by.
- Venting — core gas has to be routed out of the mold; on a part this size there is little section to absorb it.
- Internal geometry — wall thickness is the one dimension an intact original will not give up, which is why the destroyed jug was cut.
- Shape fidelity — the pattern was hand-carved, so the model follows the original contour rather than an idealised one.
Figures
The full sequence