BIZOMAT MAKEOS · Fabrication
Casting Pattern Plan (Machining Allowance, Shrinkage, Casting and Pour Weight)
For a block-shaped casting, what pattern dimensions do I make with machining and shrinkage allowances, what will the casting weigh, and how much metal must I pour?
Pattern plan for a rectangular block casting: casting dimensions with machining allowance on the machined faces of each dimension and pattern dimensions enlarged for shrinkage (as the pattern shrinkage tool, applied to length, width and height), casting volume less cores and casting mass, the metal to pour for the casting yield (gates and risers), and a check against the ladle or furnace capacity.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Finished length | mm | Finished length of the part. |
| Machined faces across the length | Number of machined faces across the length (0, 1 or 2). | |
| Finished width | mm | Finished width. |
| Machined faces across the width | Machined faces across the width. | |
| Finished height | mm | Finished height. |
| Machined faces across the height | Machined faces across the height. | |
| Machining allowance per machined face | mm | Machining allowance on each machined face. |
| Shrinkage allowance | mm/m | Pattern-maker’s shrinkage for the metal (from your foundry data). |
| Weight | ||
| Casting metal density | kg/m³ | Density of the cast metal. |
| Volume of cored-out spaces | L | Volume removed by cores. |
| Casting yield (casting ÷ metal poured) | % | Share of the poured metal that ends up in the casting (the rest is gates, risers and runners). |
| Ladle or furnace capacity | kg | Capacity of the ladle or furnace. |
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 length
- What it is
- The finished length of the machined part, before any machining allowance or shrinkage is added.
- 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.
What this means: Machined faces across the length
- What it is
- How many of the two faces at the ends of the length will be machined, each getting a machining allowance.
- 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
- Enter 0, 1 or 2: the number of machined faces, not the allowance.
What this means: Finished width
- What it is
- The finished width of the machined part, before any machining allowance or shrinkage is added.
- 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 200 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Machined faces across the width
- What it is
- How many of the two faces at the sides of the width will be machined, each getting a machining allowance.
- 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
- Enter 0, 1 or 2: the number of machined faces, not the allowance.
What this means: Finished height
- What it is
- The finished height of the machined part, before any machining allowance or shrinkage is added.
- 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 100 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Machined faces across the height
- What it is
- How many of the two faces at the top and bottom of the height will be machined, each getting a machining allowance.
- 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 1 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Enter 0, 1 or 2: the number of machined faces, not the allowance.
What this means: Machining allowance per machined face
- What it is
- The extra metal left on each machined face of the casting so it can be machined to the finished 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 in each direction.
What this means: Shrinkage allowance
- What it is
- The pattern-maker’s shrinkage allowance for the metal: how much larger the pattern is made per metre of casting length, from your foundry data.
- 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.
- Get it right
- mm per metre: 10 mm/m is 1 %.
Weight
What this means: Casting metal density
- What it is
- The density of the cast metal, used to turn casting volume into casting mass.
- 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.
What this means: Volume of cored-out spaces
- What it is
- The volume of the internal spaces formed by cores, which is removed from the block volume.
- 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.
- Get it right
- Enter litres: 1 L = 1,000,000 mm³.
What this means: Casting yield (casting ÷ metal poured)
- What it is
- The share of the metal poured that ends up in the casting; the rest goes into gates, runners and risers.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 5% to 100%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 60% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Metal to pour is inversely proportional to the casting yield.
What this means: Ladle or furnace capacity
- What it is
- The largest mass of metal the ladle or furnace can deliver in one pour.
- Units and format
- Enter a number in kg: kilograms. The form accepts 0.000001 kg to 10000000 kg. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 500 kg as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Method and formulas
- Casting dimension = finished + allowance × machined faces; pattern dimension = casting × (1 + shrinkage) (as the pattern shrinkage tool, for each dimension).
- Casting volume = product of casting dimensions − cores; mass = volume × density.
- Metal to pour = casting mass ÷ yield.
- Example: make the pattern 309.18 × 208.14 × 104.07 mm; the casting weighs 46.747 kg and needs 77.912 kg poured.
Limitations
- Rectangular block; draft, fillets and core prints are added by the pattern maker.
- Uniform shrinkage; hindered contraction in complex castings is less.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Make a pattern for a simple block casting
- Estimate metal to melt for a casting
- Check a ladle can pour a casting
Who it is for
- Pattern makers
- Foundry engineers
- Estimators
What you get
- Casting and pattern dimensions
- Casting volume and mass
- Metal to pour and the capacity check
Interpreting the result
- A low yield means heavy risers: better feeding design often saves more metal than trimming allowances.
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.
Open the Casting Pattern Plan (Machining Allowance, Shrinkage, Casting and Pour Weight) calculator