BIZOMAT MAKEOS · Engineering
Preferred Size Selection (Renard Series Size for Each Requirement, Oversize, Distinct Sizes)
For a set of required sizes or ratings, which preferred numbers should I pick, how much oversize does each choice give, and how many distinct sizes does the range need?
Selection of preferred sizes from a Renard series (R5 to R80) for up to five requirements: the ratio of the series and the preferred numbers around each requirement (as the preferred numbers tool), the smallest preferred number at or above each requirement and its rounded value, the oversize of each choice, and the number of distinct sizes, against the largest oversize you accept.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Series | choice | Renard series to choose from (finer series give smaller steps). |
| Requirement 1 (0 = unused) | First required size or rating. | |
| Requirement 2 (0 = unused) | Second requirement. | |
| Requirement 3 (0 = unused) | Third requirement. | |
| Requirement 4 (0 = unused) | Fourth requirement. | |
| Requirement 5 (0 = unused) | Fifth requirement. | |
| Largest oversize accepted | % | Largest amount a chosen size may exceed its requirement. |
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: Series
- What it is
- The Renard series of preferred numbers to choose sizes from. Each series has a fixed number of steps per decade; finer series have smaller steps between sizes.
- Units and format
- Choose one of 5 options from the list: R5 (ratio 1.58); R10 (ratio 1.26); R20 (ratio 1.12); R40 (ratio 1.06); R80 (ratio 1.03).
- Example
- The form opens with “R10 (ratio 1.26)” selected as a worked example. Choose the option that matches your case.
- Get it right
- A finer series gives less oversize but more distinct sizes to stock.
What this means: Requirement 1 (0 = unused)
- What it is
- The first size or rating you need, as a minimum, in any unit. The tool picks the smallest preferred number at or above it. 0 leaves it out.
- Units and format
- Enter a plain number with no unit. The form accepts 0 or more. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 12 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use the same unit for every requirement you want to compare; the tool rounds up, so enter the minimum you need.
What this means: Requirement 2 (0 = unused)
- What it is
- The second size or rating you need, as a minimum, rounded up to the series. 0 leaves it out.
- Units and format
- Enter a plain number with no unit. The form accepts 0 or more. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 47 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Each requirement is treated as a minimum; round down yourself where it is a maximum.
What this means: Requirement 3 (0 = unused)
- What it is
- The third size or rating you need, as a minimum, rounded up to the series. 0 leaves it out.
- Units and format
- Enter a plain number with no unit. The form accepts 0 or more. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 150 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Each requirement is treated as a minimum; round down yourself where it is a maximum.
What this means: Requirement 4 (0 = unused)
- What it is
- The fourth size or rating you need, as a minimum, rounded up to the series. 0 leaves it out.
- Units and format
- Enter a plain number with no unit. The form accepts 0 or more. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 300 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Each requirement is treated as a minimum; round down yourself where it is a maximum.
What this means: Requirement 5 (0 = unused)
- What it is
- The fifth size or rating you need, as a minimum, rounded up to the series. 0 leaves it out.
- Units and format
- Enter a plain number with no unit. The form accepts 0 or more. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 900 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Each requirement is treated as a minimum; round down yourself where it is a maximum.
What this means: Largest oversize accepted
- What it is
- The largest amount by which a chosen preferred size may exceed its requirement, as a share of the requirement.
- 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 1000%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 15% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Type the percentage itself, not a fraction.
Method and formulas
- Series ratio = 10^(1/n); preferred numbers 10^(i/n) (as the preferred numbers tool).
- Chosen size = 10^(⌈n log₁₀ r⌉ ÷ n), the smallest preferred number at or above the requirement; rounded to three figures as usually listed.
- Oversize = chosen ÷ required − 1.
- Example: the largest oversize is 11.111% with 5 distinct sizes.
Limitations
- Exact series values; the rounded values used in standards differ slightly (for example 3.15 for 3.162).
- Each requirement taken as a minimum; round down instead when the requirement is a maximum.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Choose tank, motor or pulley sizes from a preferred series
- Rationalise a product range
- See how a coarser series changes the oversize
Who it is for
- Design engineers
- Product managers
- Standards engineers
What you get
- Preferred size for each requirement
- Oversize of each
- Distinct sizes and decision
Interpreting the result
- The worst oversize of a series is its step: about 58% for R5, 26% for R10, 12% for R20.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 672. Topic reference; no source tables or recommended settings are reproduced.
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