Reference
Machine Base Constructions Compared
Five ways to build a machine base, across fourteen properties. Comparisons are qualitative where an honest answer is qualitative: a single damping multiplier quoted across a material class would be a marketing figure, not an engineering one.
| Property | Grey cast iron | Ductile iron | Welded steel | Filled weldment | Mineral cast |
|---|---|---|---|---|---|
| Typical specification | EN-GJL-250 (GG25) to EN 1561 | EN-GJS-400-15 to EN 1563 | S235 / S355 to EN 10025 | S355 shell with mineral or concrete core | Graded aggregate in epoxy binder, supplier formulation |
| Graphite form | Flake (lamellar) | Spheroidal | Not applicable | Not applicable | Not applicable |
| Relative stiffness | High | High, slightly above grey iron | Highest per unit volume | As the steel shell; fill adds little | Lowest per unit volume, compensated with section |
| Relative damping | Good | Lower than grey iron | Lowest | Good to very good | Highest |
| Relative density | High | High | High | High | Around a third of iron, near aluminium |
| Thermal conductivity | High | High | High | Reduced by the core | Low |
| Tensile behaviour | Weak, brittle fracture | Tough, yields before failure | Tough | Tough (shell carries load) | Weak; loads go through cast-in inserts |
| Tooling required | Pattern | Pattern | Fixtures only | Fixtures only | Mould |
| First-unit lead time | Months | Months | Weeks, fastest of the five | Weeks plus cure | Mould build plus long cure |
| Cost of a design change | High, pattern rework | High, pattern rework | Low, cut and re-weld | Low on the shell | Very high, the mould is the design |
| Per-unit cost trend | Falls with volume | Falls with volume | Roughly flat | Roughly flat | Falls with volume |
| Corrosion protection | Required | Required | Required | Required on the shell | Not required, inert |
| Repairable | Limited, specialist | Limited, specialist | Yes, readily | Shell yes, core no | Effectively no |
| Typical use | Repeat machine models needing damping | Shock and cyclic tensile loads | Prototypes, low volume, large envelopes | Steel design that fails a vibration target | Metrology, optical and fine finishing |
How to read this
Stiffness and damping are different properties. Welded steel is the stiffest per unit volume and the worst damped. Mineral cast is the reverse. A machine can be perfectly rigid and still chatter, so establish which problem you have before choosing a row to optimise.
Compare finished structures, not materials. Mineral cast is far less stiff per unit volume but around a third the density, so at equal mass the part is much bulkier and recovers the stiffness. Whether your envelope allows that bulk is the real question.
The cost rows matter more than the property rows. For most machines the decision is settled by tooling cost, lead time and how likely the design is to change, not by a material property.
Which guide next
- Material properties: tensile, yield, modulus, pros, cons and how common each is
- Manufacturing technologies: how each one is made
- Cast iron against welded steel: the decision most builders actually face
- Ductile against grey iron: why the weaker grade is usually correct
- Filled weldments: the option most builders never price
- Epoxy granite: when mineral cast earns its mould cost
- Polymer concrete against cast iron
Still unsure? The self-check on the home page asks six questions and suggests a construction. It runs in your browser and nothing is submitted.