Machining stock and material yield calculator

Symmetric stock allowance on a rectangular finished part.

cnc-stock-allowance.napkin / editable

SCENARIO COMPARISON

Compare the numbers.

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

Scenario	stockLengthmm	stockWidthmm
	104	54
	84	54

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.

stock length envelope104.00 mm✓ passes

BASELINE INPUTS

finishedLength100 mmfinishedWidth50 mmallowance2 mm

CALCULATED

stockLength104 mm

stockWidth54 mm

Edits change the baseline source.

THE SOURCE

Edits below update the same model.

# Machining stock and material yield
# Scope: Symmetric stock allowance on a rectangular finished part.
# Status: illustrative worked example; engineering review pending.
# Inputs are example values. Checks are editable example requirements, not standards.

finishedLength = 100 mm
finishedWidth = 50 mm
allowance = 2 mm

stockLength := finishedLength+2*allowance [mm]
stockWidth := finishedWidth+2*allowance [mm]

check stock length envelope: stockLength <= 110 mm

scenario alternative: finishedLength = 80 mm

Calculated from your source · not saved

Baseline · Baseline

stock length envelope104.00 mm ✓ passes

alternative · alternative

stock length envelope84.00 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.

stock length: stockLength = finishedLength+2*allowance [mm]
stock width: stockWidth = finishedWidth+2*allowance [mm]

Original worked example

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

Given

finished length: 100 mm
finished width: 50 mm
allowance: 2 mm

Calculated

stock length: 104 mm
stock width: 54 mm

Assumptions and limits

Symmetric stock allowance on a rectangular finished part.

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: Machining stock and material yield. Inputs: raw stock; part envelope; setup and finishing allowances. Outputs: stock requirement; removed fraction. Model scope: Tool, stock and machine-specific cutting 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: raw stock, part envelope, setup and finishing allowances
Outputs: stock requirement, removed fraction
Modes: calculate, compare, sweep
Drawing: Tool engagement and material-removal preview

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