BIZOMAT MAKEOS · Quality
Limit Gauge Plan (IT Tolerance, Go and No-Go Sizes, Makeability)
For this size and tolerance grade, what are the work limits, what go and no-go gauge sizes do I order, and is the gauge tolerance large enough to make?
Plan for go and no-go limit gauges for a hole or shaft: the IT tolerance for the size and grade (as the ISO tolerance grade tool) placed by your fundamental deviation (lower deviation of a hole, upper deviation of a shaft), the go and no-go gauge size ranges with gauge tolerance and go-gauge wear allowance as shares of the work tolerance (as the go and no-go gauge tool), and a check that the gauge tolerance is not smaller than your gauge maker can hold.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Feature | choice | Whether the feature is a hole (plug gauges) or a shaft (ring or snap gauges). |
| Nominal size | mm | Nominal size of the feature. |
| Tolerance grade | choice | IT tolerance grade. |
| Fundamental deviation (hole lower, shaft upper) | µm | Fundamental deviation from your fit standard: the lower deviation of a hole (0 for H) or the upper deviation of a shaft (0 for h). |
| Gauge tolerance (% of work tolerance) | % | Gauge-making tolerance as a share of the work tolerance. |
| Wear allowance on go gauge (% of work tolerance) | % | Wear allowance on the go gauge as a share of the work tolerance. |
| Smallest gauge tolerance your gauge maker holds | µm | Smallest gauge tolerance your gauge supplier can make. |
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: Feature
- What it is
- Whether the gauged feature is a hole, checked with go and no-go plug gauges, or a shaft, checked with ring or snap gauges.
- Units and format
- Choose one of 2 options from the list: Hole (plug gauges); Shaft (ring or snap gauges).
- Example
- The form opens with “Hole (plug gauges)” selected as a worked example. Choose the option that matches your case.
What this means: Nominal size
- What it is
- The nominal (basic) size of the hole or shaft, the size the deviation and tolerance grade are applied to.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 500 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 25 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Sets the size step for the IT tolerance.
What this means: Tolerance grade
- What it is
- The IT tolerance grade of the feature, which with the nominal size sets the width of the work tolerance.
- Units and format
- Choose one of 12 options from the list: IT5; IT6; IT7; IT8; IT9; IT10; IT11; IT12; IT13; IT14; IT15; IT16.
- Example
- The form opens with “IT7” selected as a worked example. Choose the option that matches your case.
What this means: Fundamental deviation (hole lower, shaft upper)
- What it is
- The fundamental deviation of the fit: for a hole, how far its lower limit is from nominal; for a shaft, how far its upper limit is from nominal, from your fit standard.
- Units and format
- Enter a number in µm: micrometres (µm, microns). The form accepts -5000 µm to 5000 µm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0 µm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Enter micrometres with the sign from the standard; it is zero for an H hole or an h shaft.
What this means: Gauge tolerance (% of work tolerance)
- What it is
- The tolerance allowed for making each gauge, as a share of the work tolerance, from your gauging standard or quality rules.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 50%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger share makes gauges easier to make but rejects more good parts.
- Get it right
- Gauge tolerance plus wear allowance must be less than the work tolerance.
What this means: Wear allowance on go gauge (% of work tolerance)
- What it is
- The wear allowance built into the go gauge, as a share of the work tolerance, so it stays inside the limits as it wears.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 50%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 5% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Only the go gauge carries a wear allowance; the no-go gauge rarely wears.
What this means: Smallest gauge tolerance your gauge maker holds
- What it is
- The tightest gauge-making tolerance your gauge supplier can hold, from their capability statement.
- Units and format
- Enter a number in µm: micrometres (µm, microns). The form accepts 0 µm to 100 µm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1 µm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Enter micrometres, not millimetres.
Method and formulas
- IT value from the standard tolerance unit for the size step (as the ISO tolerance grade tool); hole: lower = size + EI, upper = lower + IT; shaft: upper = size + es, lower = upper − IT.
- Go gauge at the maximum-material limit plus wear allowance; no-go at the least-material limit; each with the gauge tolerance inside the work limits (as the go and no-go gauge tool).
- Makeable if the gauge tolerance is not below the gauge maker’s limit.
- Example: limits 25–25.021 mm (IT 20.918 µm); go 25.001–25.003 mm, no-go 25.019–25.021 mm.
Limitations
- Gauge tolerance and wear allowance set as shares of the work tolerance; your gauge standard may set them differently.
- Sizes up to 500 mm.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Order plug or ring gauges for a toleranced feature
- Check whether a grade can be gauged by fixed gauges
- Set gauge sizes on an inspection plan
Who it is for
- Quality engineers
- Inspectors
- Toolroom staff
What you get
- Work tolerance and limits
- Go and no-go gauge size ranges
- Gauge makeability
Interpreting the result
- Fine grades leave very little gauge tolerance: below about IT6 measure with comparators instead of fixed gauges.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 661–663, 705–708, 635–668. Topic reference; no source tables or recommended settings are reproduced.
- ISO 286-1:2010 Geometrical product specifications (GPS) — ISO code system for tolerances on linear sizes
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Open the Limit Gauge Plan (IT Tolerance, Go and No-Go Sizes, Makeability) calculator