KEVOS® MAKEOS · Quality
Standard Metal Ball Lot Check (Lot Mean Diameter, Ball Gauge, Specific Diameter, Balls per Kilogram)
For a lot of precision metal balls ordered by nominal diameter, grade and ball gauge, is the measured lot mean diameter and lot variation within what I allow for the grade, what specific diameter should the package be marked with, and how many balls are there per kilogram?
Lot check and package marking for standard metal balls in the terms of ANSI/AFBMA Std 10 as described in the handbook: the lot mean diameter DwmL from the mean diameters of the largest and smallest balls, the lot diameter variation VDwL, the size the order asks for (nominal diameter plus the ball gauge), acceptance between the limits you enter for the grade, the specific diameter (lot mean diameter rounded to the container marking increment, less the nominal diameter) for the package label, and the number of balls per kilogram and the lot mass from the material density.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Nominal ball diameter Dw | mm | Nominal diameter used to identify the ball size, for example 6 mm or 1/4 in (6.35 mm). |
| Ball gauge ordered (with sign) | µm | Ball gauge on the order: the small signed amount by which the lot mean diameter should differ from the nominal diameter (0 is “OK”). |
| Allowed lot mean diameter below the ordered size | µm | How far the lot mean diameter may fall below the ordered size (nominal plus ball gauge) for the grade, from the standard or your agreement with the maker. |
| Allowed lot mean diameter above the ordered size | µm | How far the lot mean diameter may lie above the ordered size for the grade. |
| Container marking increment for the grade | µm | Container marking increment for the grade from the standard’s Table 1, the step to which the specific diameter is rounded. |
| Allowed lot diameter variation for the grade | µm | Allowed lot diameter variation for the grade from the standard’s Table 1. |
| Measured lot | ||
| Mean diameter of the largest ball | mm | Mean diameter (average of largest and smallest single diameters) of the largest ball found in the lot. |
| Mean diameter of the smallest ball | mm | Mean diameter of the smallest ball found in the lot. |
| Count and mass | ||
| Density of the ball material | kg/m³ | Density of the ball material from your material data; the handbook lists, for example, 7833 kg/m³ for chrome alloy steel. |
| Number of balls in the lot | balls | Number of balls in the lot or package, for the lot mass. |
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: Nominal ball diameter Dw
- What it is
- Nominal diameter used to identify the ball size on the order.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 6 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 ordered size, the specific diameter and the count per kilogram.
- Get it right
- For inch balls enter the nominal size in mm (1/4 in = 6.35 mm).
What this means: Ball gauge ordered (with sign)
- What it is
- Ball gauge on the order: the signed amount the lot mean diameter should differ from nominal.
- Units and format
- Enter a number in µm: micrometres (µm, microns). The form accepts -1000 µm to 1000 µm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with -4 µm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Moves the ordered size and both acceptance limits.
- Get it right
- Choose from the preferred ball gauges for the grade; 0 is called “OK”.
What this means: Allowed lot mean diameter below the ordered size
- What it is
- How far the lot mean diameter may fall below the ordered size for the grade.
- Units and format
- Enter a number in µm: micrometres (µm, microns). The form accepts 0 µm to 1000 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.
- Effect on the result
- Sets the lower acceptance limit.
- Get it right
- Take it from the standard or your agreement with the ball maker.
What this means: Allowed lot mean diameter above the ordered size
- What it is
- How far the lot mean diameter may lie above the ordered size for the grade.
- Units and format
- Enter a number in µm: micrometres (µm, microns). The form accepts 0 µm to 1000 µm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.25 µm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Sets the upper acceptance limit.
- Get it right
- Take it from the standard or your agreement with the ball maker.
What this means: Container marking increment for the grade
- What it is
- Container marking increment for the grade, the step the specific diameter is rounded to.
- Units and format
- Enter a number in µm: micrometres (µm, microns). The form accepts 0.000001 µm to 100 µm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.25 µm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Changes only the rounding of the specific diameter.
- Get it right
- Read it from Table 1 of the ball standard for the grade.
What this means: Allowed lot diameter variation for the grade
- What it is
- Allowed lot diameter variation for the grade, the largest spread of ball mean diameters.
- Units and format
- Enter a number in µm: micrometres (µm, microns). The form accepts 0.000001 µm to 1000 µm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.8 µm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Rejects the lot when the measured spread is larger.
- Get it right
- Read it from Table 1 of the ball standard for the grade.
Measured lot
What this means: Mean diameter of the largest ball
- What it is
- Mean diameter of the largest ball measured in the lot.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 5.9964 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Raises the lot mean diameter and the lot variation.
- Get it right
- Average the largest and smallest single diameters of that ball.
What this means: Mean diameter of the smallest ball
- What it is
- Mean diameter of the smallest ball measured in the lot.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 5.99614 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Lowers the lot mean diameter and widens the lot variation.
- Get it right
- Average the largest and smallest single diameters of that ball.
Count and mass
What this means: Density of the ball material
- What it is
- Density of the ball material, for the count per kilogram and the lot mass.
- Units and format
- Enter a number in kg/m³: kilograms per cubic metre. The form accepts 0.000001 kg/m³ to 30000 kg/m³. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 7833 kg/m³ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Denser balls give fewer per kilogram.
- Get it right
- The handbook lists 7833 kg/m³ for chrome alloy steel and 14947 kg/m³ for tungsten carbide.
What this means: Number of balls in the lot
- What it is
- Number of balls in the lot or package being checked.
- Units and format
- Enter a number in balls: balls. The form accepts 1 balls or more. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 5000 balls as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Only changes the lot mass.
- Get it right
- Take it from the order or the package label.
Method and formulas
- DwmL = (mean diameter of the largest ball + mean diameter of the smallest ball) ÷ 2; VDwL = their difference.
- Ordered size = Dw + ball gauge; the lot is accepted when DwmL lies within the limits entered and VDwL does not exceed the allowed variation.
- Ball gauge deviation S = DwmL − (Dw + ball gauge).
- Specific diameter = DwmL rounded to the container marking increment − Dw.
- Balls per kilogram = 1 ÷ (π/6 Dw³ ρ), which is the handbook’s 1,910,000 ÷ (Dw³ ρ) with Dw in mm and ρ in g/cm³.
- Example: 6 mm balls ordered at -4 µm ball gauge measuring 5.9963 mm lot mean are marked with a specific diameter of -3.75 µm; there are about 1,128.8 balls per kilogram.
Limitations
- Grade tolerances, marking increments and ball gauges come from ANSI/AFBMA Std 10 (or ISO 3290) and the order; enter them, they are not built in.
- The check covers the lot size; individual ball diameter variation, form, roughness and hardness are checked separately.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Accept or reject a delivered lot of bearing or valve balls
- Work out the specific diameter for a package label
- Estimate how many balls a weighed quantity contains
Who it is for
- Quality inspectors
- Bearing and valve assemblers
- Purchasing and stores
What you get
- Lot mean diameter and lot diameter variation
- Ordered size and acceptance limits
- Ball gauge deviation
- Specific diameter to mark on the package
- Balls per kilogram and lot mass
Interpreting the result
- A lot outside its limits may still suit another ball gauge; the specific diameter shows where it falls.
- Rounding is to the nearest marking increment.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3355–3357, 3361–3362. Topic reference; no source tables or recommended settings are reproduced.
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