Expressing Tolerances for Small Cutting Tools: Upper and Lower Deviations, Plus/Minus Signs, and Chinese-Language Marking
Using dimensional tolerance formulas and worked examples, this article explains the relationships among negative deviations, bilateral tolerances, superscripts and subscripts, and the permissible size range.
Small cutting tools have very small dimensions, but the information conveyed by tolerance symbols is far from small. Negative signs, plus/minus signs, and deviations stacked above and below one another all take part in defining the permissible range. When reading a drawing, check the symbols, the direction of the deviations, and the units in full to avoid misjudging the permissible size.
A one-sided negative deviation is not a bilateral tolerance
Example of a deviation for the tool nose radius: the upper deviation is 0, and the lower deviation is −0.05 mm.This marking indicates that the permissible value cannot be higher than the nominal value, and the lower limit is determined by the negative deviation. It differs from a bilateral tolerance centered on the nominal value. Here the symbol RE stands for the tool nose radius; this example is for reading markings and does not claim that any given model uses the same tolerance.
Example of a dimensional deviation: retain the letter, the upper and lower positions, the negative sign, and the decimal places.Bilateral tolerances and the permissible range
Self-prepared range example: ±0.10 mm corresponds to symmetric upper and lower limits.Taking a nominal length of 10.00 mm as an example, ±0.10 mm corresponds to a lower limit of 9.90 mm and an upper limit of 10.10 mm. This standalone worked example only demonstrates the arithmetic relationship; it does not use the source page to make any dimensional commitment for any specific tool model.
Annotation type | Upper deviation | Lower deviation | Explanation |
|---|---|---|---|
Arc radius example | 0 mm | −0.05 mm | Unilateral negative deviation |
Dimension example | 0 mm | −0.02 mm | Unilateral negative deviation |
Standalone length calculation example | +0.10 mm | −0.10 mm | Bilateral symmetric tolerance |
Dimension name and deviation direction
The dimension name, nominal value, upper deviation and lower deviation should each be checked separately. For a unilateral negative deviation, the upper limit is the nominal value and the lower limit is determined by the negative deviation; for a bilateral symmetric tolerance, the permissible range extends on both sides of the nominal value, and the two must not be treated as the same requirement.
When reading a tolerance, compare the letters, plus and minus signs, decimal places, superscripts and subscripts, units and permissible range item by item, and confirm whether a unilateral deviation or a bilateral tolerance is specified. Dimensional acceptance should satisfy both the symbol definition and the upper and lower limit requirements.
This article is a tolerance reading case study. When ordering, inspecting, or preparing machining programs, use the latest drawings and catalogs for the actual model, and verify according to the measurement method approved by your company.
Source note: This article was originally written based on the public technical materials listed, and the calculation examples have been independently recalculated.
Mitsubishi Materials: Overview of small cutting tools: https://www.mmc-carbide.com/cn/technical_information/tec_turning_tools/small_tools/guide/tec_small_tools_outline