Casting patterns fall into eleven recognized types, and what separates them is not the shape of the part but how the pattern is divided and how it is held: one solid body, split at a parting line, broken into several sections, or mounted on plates for repeat production.
That choice gets paid for twice — once in the tooling quote, and again in every casting the pattern makes, because the pattern equipment sets the tolerance band the foundry can hold. Between the loosest and the tightest arrangement, that band is roughly a factor of two.
| Pattern type | Description | Best suited for |
|---|---|---|
| Single-piece pattern | Entire casting shape is made as one solid piece | Simple, low-volume castings |
| Split pattern | Pattern is divided into two sections along the parting line | Medium-complexity castings |
| Multi-piece pattern | Pattern consists of three or more sections | Complex shapes |
| Match-plate pattern | Cope and drag halves are mounted on opposite sides of one plate | High-volume production |
| Cope-and-drag pattern | Cope and drag halves are mounted on separate plates | Large or automated castings |
| Gated pattern | Several patterns are connected by a common runner and gating system | Producing multiple castings per mold |
| Loose-piece pattern | Removable pieces allow patterns with undercuts or projections to be withdrawn | Complex components |
| Follow-board pattern | A supporting board holds weak or irregular patterns during molding | Thin or fragile patterns |
| Sweep pattern | A shaped template rotates around an axis to form the mold cavity | Large circular castings |
| Skeleton pattern | An open framework defines the casting shape | Very large, low-volume castings |
| Segmental pattern | A section of the pattern is repeatedly moved around a center | Large symmetrical castings |
1. Single-Piece or Solid Pattern
A single-piece pattern carries the whole casting shape as one solid body with no built-in split, and it suits simple parts in low quantity — a gray iron counterweight built to order, not a housing on a production line.
Used loose — unmounted, with nothing tying it to the flask — it is also the least accurate pattern equipment a sand foundry runs. The molder sets it, rams it, rolls the mold over and draws it by hand, so the pattern’s position relative to the flask pins is established fresh on every mold.
SFSA’s published comparison of pattern equipment puts loose wood patterns at 210 on an index where a metal match plate is 100 — roughly double the tolerance band on the same part in the same green sand.
The constraint is geometry rather than quantity: the entire shape has to withdraw from the mold joint in one direction, so a single undercut rules the type out.
2. Split Pattern
A split pattern is the same shape divided into two halves along the parting line, one molded in the cope and one in the drag, which lets shapes that cannot be drawn in one direction be molded without loose pieces or extra cores. It is the workhorse for moderately complex castings.
The split itself is routine; where it is placed is the tolerance decision. Dimensions that cross the parting line run about 24% more variable than dimensions formed entirely within one mold half, because they depend on how cope and drag close on each other rather than on one piece of tooling.
So the practical rule is short: whatever the drawing calls critical, ask for it to sit inside one half of the mold. When a critical dimension has to span the joint, budget for the extra spread instead of discovering it at first article.
3. Multi-Piece Pattern
A multi-piece pattern splits the shape into three or more sections, and it is used when two halves cannot clear the geometry — a part with more than one parting plane, or with features that pull in different directions.
Every additional piece of tooling that helps form a dimension adds a degree of freedom. A feature made entirely by one piece of tooling is as accurate as that piece; a feature made between two pieces also carries whatever error there is in how they locate to each other. Features formed between the mold and a core, for example, run about 39% more variable than features formed within a single mold half.
That is why multi-piece construction is a last resort rather than a capability to show off. When it is unavoidable, decide before the tooling is cut which features must be held, and arrange the sections so those features are formed by a single piece — otherwise the patternmaker will make that call for you, on convenience grounds.
4. Match-Plate Pattern
A match-plate pattern mounts the cope and drag halves on opposite faces of one plate, indexed to the same flask pins, and it is the dimensional benchmark for sand molding as well as the standard arrangement for volume production.
Because both halves are located by the same plate, the cope-to-drag relationship is built into the tooling instead of being re-established at every closing. In SFSA’s dimensional study of production steel castings, using separate cope and drag instead of a match plate added 0.03 in. (0.8 mm) of 6σ spread.
Pattern condition carries a penalty of similar size: a very poor pattern costs 0.04 in. (1 mm) against one in good condition. A match plate that has run for years without refacing is not automatically better than well-maintained separate boards.
5. Cope-and-Drag Pattern
A cope-and-drag pattern puts the two halves on separate plates so they can be molded in separate flasks, often on separate machines, and joined at closing. It exists for size and handling — parts and flasks too large to mold practically from one plate.
It is a size solution, not an accuracy upgrade. The 0.03 in. (0.8 mm) of added variability named under match plates above is precisely the cost of leaving the match plate behind; separate boards buy flask size and line flexibility, and they are paid for in tolerance.
6. Gated Pattern
A gated pattern joins several pattern impressions to a common runner and gating system, so one mold yields several castings and the gating is built into the tooling instead of being cut by hand.
The gain is molds per hour and consistency: every mold is gated identically, so feeding behavior does not depend on which molder ran the flask.
The limit is size. Gated tooling only pays where several parts fit one flask, which for medium and large ferrous castings means the small end of the range — above that, one casting per mold with its own gating and risering is the norm.
7. Loose-Piece Pattern
A loose-piece pattern carries removable sections that stay behind in the sand when the main body is drawn and then come out separately through the cavity, which is how an undercut or a side projection gets molded without splitting the pattern further.
The cost is per-mold handling. Every loose piece is set, rammed around and picked out by hand, so molding is slower and the piece can shift — which puts the variation directly on the feature it forms. Check whether a core can produce the same undercut before accepting one.
8. Follow-Board Pattern
A follow-board pattern is molded on a shaped board cut to match the pattern’s underside, which supports the pattern during ramming and establishes a parting line where the shape itself offers no flat joint.
It answers two problems: a pattern too thin or too fragile to survive ramming unsupported, and an irregular pattern whose natural parting surface is curved. The board is tooling, not part of the casting shape — it is used to make the drag, then replaced by the finished drag when the cope is rammed.
9. Sweep Pattern
A sweep pattern is a profile board rotated about a fixed spindle to cut the mold cavity directly in the sand, so no full pattern is built at all. It suits large circular and symmetrical shapes.
The economics are the whole point. For a large flywheel rim or a heavy ring section in a quantity of one or two, the tooling is a board and a spindle rather than a pattern the size of the part.
The price is molding time and skill. The shape comes from the molder’s operation of the sweep instead of from tooling, and the geometry is limited to what a rotated profile can generate.
10. Skeleton Pattern
A skeleton pattern is an open framework of ribs and boards defining the outline of the casting, with sand packed and struck off between the members to complete the shape. It belongs on very large, one-off parts where a solid pattern would cost more than the casting.
Accuracy comes from the molder’s strickle work rather than from tooling, so the type fits where the part is large, the quantity small, the tolerances generous, and enough machining stock is carried to cover what the mold does not hold.
11. Segmental Pattern
A segmental pattern is one section of a symmetrical shape, molded repeatedly around a center to build up the full cavity — a large ring molded as, say, one sixth of itself and indexed six times.
It saves the same money a sweep does and applies where the shape is a repeating segment rather than a simple profile of revolution. It also carries the same weakness as multi-piece tooling: every repositioning is a fresh chance for the segment to sit slightly off, and the cavity is only as true as the sum of those settings.
How to Choose a Casting Pattern
Quantity decides the pattern equipment, and geometry decides the pattern’s construction. Answer those two in that order and the table below resolves most cases.
Quantity comes first because it buys tolerance outright. SFSA publishes its sand casting tolerance grades in two sets, short production series and long, and the long-series grades are one full CT grade tighter across every condition — CT 10-12 instead of CT 11-13 for the conditions that cover most casting types and sand molding processes.
Pattern material follows quantity too. Wood wears and moves with humidity and temperature, and wear does more than widen the spread — it drifts the average dimension over a run, which is why wear surfaces get faced with metal and why long runs go to metal patterns on rigid plates.
Geometry then sets the construction: whether the shape draws in one direction, needs one joint, needs more than one, or has undercuts that a core cannot conveniently form. Size and quantity together set the mounting — loose, separate cope and drag boards, or a match plate.
| Requirement | Common choice |
|---|---|
| Simple casting + low production | Single-piece pattern |
| Moderately complex casting | Split pattern |
| Very complicated geometry | Multi-piece or loose-piece pattern |
| High-volume sand casting | Match-plate pattern |
| Large mechanized casting | Cope-and-drag pattern |
| Several components per mold | Gated pattern |
| Large circular casting | Sweep pattern |
| Very large, low-volume component | Skeleton pattern |
| Large circular or symmetrical component | Segmental pattern |
| Thin or fragile pattern | Follow-board pattern |
Two things are worth telling the foundry before the tooling is quoted: the annual quantity you actually expect, and which dimensions on the drawing are critical. The first sets the tooling material and mounting; the second decides where the parting line goes and which features get held on a single piece of tooling.
Conclusion
The eleven types are three decisions in disguise — how the pattern is split, how it is mounted, and what it is made of. The split follows the geometry, the mounting follows the quantity, and the material follows how long the pattern has to hold its dimensions.
The one number worth carrying out of this: a loose pattern holds roughly double the tolerance band of a metal match plate on the same part in the same sand. That gap is settled when the tooling is ordered, not on the molding floor.