CALCULATORS / MOLDING, CASTING AND TOOLING

Mold and casting shrink allowance calculator

Isotropic linear tool compensation from supplied measured mold shrinkage.

molding-shrinkage.napkin / editable

SCENARIO COMPARISON

Compare the numbers.

This source describes an analytical model. Its quantities and checks are the view.

Scenario	toolSizemm	allowancemm
	101.523	1.52284
	81.2183	1.21827

All calculated quantities are listed with the inputs. Switch to Source to inspect the equations.

SCENARIOS / CALCULATED VALUESSAME SOURCE

Change an input to see the consequences.

tool envelope101.52 mm✓ passes

BASELINE INPUTS

partSize100 mmfraction0.015

CALCULATED

toolSize101.52 mm

allowance1.5228 mm

Edits change the baseline source.

THE SOURCE

Edits below update the same model.

# Mold and casting shrink allowance
# Scope: Isotropic linear tool compensation from supplied measured mold shrinkage.
# Status: illustrative worked example; engineering review pending.
# Inputs are example values. Checks are editable example requirements, not standards.

partSize = 100 mm
fraction = 0.015

toolSize := partSize/(1-fraction) [mm]
allowance := toolSize-partSize [mm]

check tool envelope: toolSize <= 103 mm

scenario alternative: partSize = 80 mm

Calculated from your source · not saved

Baseline · Baseline

tool envelope101.52 mm ✓ passes

alternative · alternative

tool envelope81.22 mm ✓ passes

Illustrative first-order example. Checks are editable requirements, not design standards. The broader topic may require additional equations, data, and validation.

Formula and units

This example uses the following equations. Input names and units match the editable source above.

tool size: toolSize = partSize/(1-fraction) [mm]
allowance: allowance = toolSize-partSize [mm]

Original worked example

These are the baseline values in the downloadable source. Edits above let you test your own values.

Given

part size: 100 mm
fraction: 0.015

Calculated

tool size: 101.523 mm
allowance: 1.52284 mm

Assumptions and limits

Isotropic linear tool compensation from supplied measured mold shrinkage.

The requirement checks use the limits written in this example. Passing a check does not establish that the model covers every load, material behavior, or operating condition in a real design.

Download this .napkin example ↓

Take it further with your agent

Napkin keeps the inputs, equations, checks and assumptions together in one study. Your agent sets it up; you change the numbers.

Try with Claude ↗

codex 'Use Napkin (https://napkin.engineering/mcp, or the local Napkin plugin) to build a study: Mold and casting shrink allowance. Inputs: target dimensions; directional shrink data; tolerances. Outputs: tool dimensions; expected dimension interval. Model scope: Early process estimates with material and supplier data. Read napkin_capabilities and the current snapshot. Ask me for the values that matter, label assumptions with units, author .napkin source, validate it and apply it with napkin_source using the current revision, then open the study. Add checks for the limits I supply. Keep unsupported analyses explicit.'

Claude needs the Napkin connector; Codex needs the Napkin plugin. Set up your agent ↗

The broader study

The topic brief below describes the broader scope. The worked example above states the particular calculation it implements.

Inputs: target dimensions, directional shrink data, tolerances
Outputs: tool dimensions, expected dimension interval
Modes: calculate, compare, sweep
Drawing: Part, cavity and runner diagram

EXECUTABLE WORKED EXAMPLE · FIRST-ORDER MODEL · CHECK THE SCOPE & ASSUMPTIONS