BIZOMAT MAKEOS · Fabrication
Pattern Size for Shrinkage and Casting Weight from Pattern
How big must the pattern be to give this casting size, and roughly what will the casting weigh?
Pattern dimension for a casting from the finished dimension, machining allowance and the metal’s shrinkage allowance (as a percentage or millimetres per metre), and the approximate casting weight from the pattern weight and the densities of the metal and the pattern material.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Finished part dimension | mm | Dimension on the finished part. |
| Machining allowance per machined face | mm | Stock left on each machined face. |
| Machined faces across this dimension | How many faces across this dimension are machined (0, 1 or 2). | |
| Shrinkage allowance | mm/m | Shrinkage allowance for the metal and casting (from your foundry or the handbook’s list). |
| Casting weight from pattern | ||
| Pattern weight | kg | Weight of the pattern. |
| Pattern material density | kg/m³ | Density of the pattern material (wood about 400–700 kg/m³). |
| Casting metal density | kg/m³ | Density of the casting metal. |
| Volume of cored-out spaces | L | Volume removed by cores that the pattern does not show. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Finished part dimension
- What it is
- The dimension on the finished, machined part that the pattern must produce after shrinkage and machining.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 300 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The pattern dimension is proportional to the casting dimension.
- Get it right
- Work one dimension at a time; length, width and height can each have different machined faces.
What this means: Machining allowance per machined face
- What it is
- The extra metal left on each machined face across this dimension, so the casting can be cleaned up to size.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 100 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- This is per face; the tool multiplies it by the number of machined faces.
What this means: Machined faces across this dimension
- What it is
- How many of the two faces across this dimension will be machined: none, one or both.
- Units and format
- Enter a plain number with no unit. The form accepts 0 to 2. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- A bore machined all round counts as two faces across its diameter.
What this means: Shrinkage allowance
- What it is
- The amount the metal contracts as the casting cools, stated per metre of length. The pattern is made larger by this amount.
- Units and format
- Enter a number in mm/m: mm/m. The form accepts 0 mm/m to 50 mm/m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10.4 mm/m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Each millimetre per metre adds one thousandth of the casting size to the pattern.
- Get it right
- Confirm with your foundry for the alloy and section; values vary with restraint and section size.
Casting weight from pattern
What this means: Pattern weight
- What it is
- The weight of the finished pattern, weighed on scales, used to estimate the casting weight by the ratio of densities.
- Units and format
- Enter a number in kg: kilograms. The form accepts 0 kg to 1000000 kg. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 4 kg as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The casting weight estimate is directly proportional to it.
- Get it right
- Weigh the pattern without core prints or loose pieces that do not form metal.
What this means: Pattern material density
- What it is
- The density of the material the pattern is made from, such as timber, resin or metal.
- Units and format
- Enter a number in kg/m³: kilograms per cubic metre. The form accepts 0.000001 kg/m³ to 25000 kg/m³. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 500 kg/m³ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A denser pattern material gives a smaller casting weight estimate.
- Get it right
- Use the density of the actual pattern stock, from the supplier or by weighing a known volume.
What this means: Casting metal density
- What it is
- The density of the metal being cast, from the alloy supplier or a standard reference.
- Units and format
- Enter a number in kg/m³: kilograms per cubic metre. The form accepts 0.000001 kg/m³ to 25000 kg/m³. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 7200 kg/m³ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The casting weight estimate is directly proportional to it.
- Get it right
- Use the density of the cast alloy, not a wrought grade, if they differ.
What this means: Volume of cored-out spaces
- What it is
- The volume of internal spaces formed by cores that the solid pattern does not show. The tool removes the metal that would fill it.
- Units and format
- Enter a number in L: litres. The form accepts 0 L to 1000000 L. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0 L as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Each litre removes one litre of metal at the casting density.
- Get it right
- This is in litres; 1 L is 1,000,000 mm³.
Method and formulas
- Casting size = finished size + machining allowance × machined faces.
- Pattern size = casting size × (1 + shrinkage ÷ 1000) with shrinkage in mm per metre.
- Casting weight ≈ pattern weight × metal density ÷ pattern density, less the weight of cored spaces (the handbook gives this as ratio factors per pattern material).
- Example: a 300 mm dimension needs a 309.18 mm pattern at 10.4 mm/m.
Limitations
- Shrinkage varies with section size, restraint and alloy; confirm with the foundry.
- Pattern weight method assumes a solid pattern of uniform density without core prints.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size a pattern or die cavity for a casting
- Check a pattern maker’s shrink rule
- Estimate casting weight for a quote from the pattern
Who it is for
- Pattern makers
- Foundry engineers
- Estimators
What you get
- Casting dimension before machining
- Pattern dimension
- Approximate casting weight
Interpreting the result
- Hindered contraction (cores, flanges) shrinks less than free contraction; foundries adjust allowances by feature.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1414, 1419. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · Library collection
Designing parts for casting: walls, draft, cores, shrinkage and working with your foundry
What it covers: How solidification shapes casting design, the rules for wall thickness, fillets, draft, cores and machining allowances, how to choose between sand and die casting on volume, and how to avoid porosity.
Method explained here · BIZOMAT original book
Patterns and allowances
In Metal Casting by the Numbers
What it covers: Sizing a pattern so the casting comes out right: shrinkage and machining allowances, draft and cores, casting mass and metal poured, and a pattern made to the wrong shrinkage rule.
BIZOMAT tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
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