Tolerances Flóra Hajdu B406 hajdfl@sze.hu

Content Tolerances Plus- and –minus tolerance Fits and allowances Geometric tolerances 2019.04.26. Hajdu Flóra

Tolerances Exact dimensions and shapes could not be atttained in the manufacture of materials and products Tolerances are the permissible variations in the specified form, size or locations of individual surfaces of part from that shown on the drawing The finished form and size into which material is to be fabricated are defined on a drawing by various geometric shapes and dimensions Generally most parts require only a few features to be held to high accuracy In order to assembled parts function properly and to allow for interchangeable manufacturing it is necessary to permit only a certain amount of tolerance on each of the mating parts and certain amount of allowance between them 2019.04.26. Hajdu Flóra

Terminology Actual size: measured size Basic size: theoretical size from which the limits for that dimension are derived by the application of the allowance and tolerance Design size: refers to the size from which the limits of size are derived by the application of tolerances Limits of size: maximum and minimum sizes permissible for a specific dimension Nominal size: the designation used for the purpose of general identification Tolerance: the total permissible variation in the size of a dimension Bilateral tolerance: variation is permitted in both directions from the specified dimension Unilateral tolerance: variation is permitted only one direction from the specified dimension Maximum material size: limit of size of a feature that results in the part containing the amount of material. Thus it is the maximum limit of size for a shaft or an external feature or athe minimum limit of size for a hole or internal feture 2019.04.26. Hajdu Flóra

Tolerancing All dimensions required in the manufacture of a product have a tolerance, except those who are identified as reference, maximum, minimum or stock Tolerances may be expressed in one of the following ways: As specified limits of tolerances shown directly on the drawing for a specified dimension As plus and minus tolerancing Combining the dimension with a tolerance symbol In a general tolerance note referring to all dimensions on the drawing for which tolerances are not utherwise specified In the form of a note referring to specific dimensions Tolerances on dimensions that locate features may be applied directly to the locating dimensions or by the position tolerancing method Tolerancing applicable to the control of form and runout referred to as geometric tolerancing 2019.04.26. Hajdu Flóra

Direct tolerancing methods A tolerance applied directly to a dimension may be expressed in 2 ways Limit dimensioning Plus-and-Minus Tolerancing Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design 2019.04.26. Hajdu Flóra

Plus-and-Minus Tolerancing 2019.04.26. Hajdu Flóra

Tolerance accumulation It is necessary to consider the effect of each tolerance with respect to other tolerances and not to permit a chain of tolerances to buid up a cumulative tolerance When the position of a surface in any one direction is controlled by more than one tolerance the tolerances are cummulative 2019.04.26. Hajdu Flóra

Dimension method comaprison Chain dimensioning: the maximum variation between any 2 features is equal to the sum of tolerances on the intermediate distances. Greatest tolerance accumulation Datum dimensioning: the maximum variation between any 2 features is equal to the sum of tolerances on the 2 dimensions from the datum to the feature. Reduced tolerance accumulation Direct Dimensioning: The maximum variation between any 2 features is controlled by the tolerance on the dimension between the features. Least tolerance accumulation Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design 2019.04.26. Hajdu Flóra

Dimension chain tolerance calculation Dimension tolerance calculations are necessary in case of: Product design: to check if the dimensions are inside the given tolerances Manufacturing design: check reference dimensions and their tolerances 2019.04.26. Hajdu Flóra

Dimension chain tolerance calculation 𝐴 1 = 100 −0.1 +0.2 𝐴 2 = 20 −0.3 +0.2 𝐴 0𝑚𝑎𝑥 = 𝐴 1max − 𝐴 2min =100.2−19.7=80.5 𝐴 0𝑚𝑖𝑛 = 𝐴 1𝑚𝑖𝑛 − 𝐴 2max =99.9−20.2=79.7 𝐴 0 = 80 −0.3 +0.5 2019.04.26. Hajdu Flóra

Fits and allowances In order that assembled parts function properly and to allow for interchangeable manufacturing it is permit only a certain amount of tolerance on each of the mating parts and a certain amount of allowance between them Fits: the fit between 2 mating parts is the relationship between them with respect to the amount of clearance or interference present when they are assembled Allowance: an international difference between the maximum material limits of mating parts 2019.04.26. Hajdu Flóra

Terminology Basic size: the size to which limits or deviations are assigned Deviation: The algebraic difference between a size and the corresponding basic size Upper deviation: The algebraic difference between the maximum limit of size and the corresponding basic size Lower deviation: The algebraic difference between the minimum limit of size and the corresponding basic size Tolerance: The difference between the maximum and minimum size limits on a part Tolerance zone: A zone representing the tolerance and its position in relation to the basic size Fundamental deviation: The deviation closest to the basic size 2019.04.26. Hajdu Flóra

Terminology Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design 2019.04.26. Hajdu Flóra

Fundamental deviation - shafts 2019.04.26. Hajdu Flóra

Fundamental deviation - holes 2019.04.26. Hajdu Flóra

International tolerance grade Establishes the magnitude of the tolerance zone Identified by prefix IT + grade number (e.g. IT6) The smaller the grade the smaller the tolerance zone Grade 1-4: very precise grades intented primarily for gage making and similar precision work Grade 5-16: a progressive series suitable for cutting operations, such as turning, boring, grinding, milling and sawing Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design scan 2019.04.26. Hajdu Flóra

Calculating tolerance 𝑇=𝑞∙𝑖 𝑖=0.45 3 𝐷 +0.001D 𝑞 𝑛 = 5 10 𝑛−1 2019.04.26. Hajdu Flóra

Example ∅20𝑠7 𝐷= 18∙30 =23.24 𝑖=0,45 3 𝐷 +0,001𝐷=0,45 3 23,24 +0,001∙23.24 𝑖=1.3 𝑞= 5 10 7−1 =15.85 𝑇=𝑞𝑖=15.85∙1.3=20.6≈21 𝜇 2019.04.26. Hajdu Flóra

Example N=20 FD=0,035 LD=FD=0,035 UD=FD+T=0,035 +0,021=0,056 Max size=20+ 𝑈𝐷=20+ 0,056=20,056 2019.04.26. Hajdu Flóra

Dimensions with tolerances 2019.04.26. Hajdu Flóra

Dimensions with tolerances 2019.04.26. Hajdu Flóra

Geometric tolerances 2019.04.26. Hajdu Flóra

Summary Tolerances Direct tolerancing methods Fits Tolerance calculations Next week: Surface finish

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