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All rights reserved. Maximum Material Requirement Least Material Requirement Theoretically exact dimensions Projected Tolerance Zonee Envelope Requirement Common zone Datum targets Free State tolerances These notes attept to clarify the meanings of the supplimentary symbols used for geometric tolerancing. The notes are outline in nature. Detailed notes are found in the identified standards and it is suggested that these standards are consulted for clearest understanding of the requirements.
Note: The following descriptions are very much shortened versions of those found in the standards and are not considered to be definitive. Used when defining a reference surface using one or more daturm target features LMC: Least material condition of a component at that limit of size where the material of the feature is at its minimum everywhere, e.
LMVS :The size generated by the collective effect of the least material size, LMS, of a feature and the geometrical tolerance form, orientation or location. LMVC: Least material virtual condition. The condition of a component of least material virtual size. LMR: Least material requirement, defining a geometrical feature of the same type and of perfect form, with a given dimension equal to LMVS, which limits a a feature on the inside of the material e.
MMS :Maximum material size; The size of the maximum material condition. MMVC:Maximum material virtual condition, is a perfect form condition of the feature.
MMVS:Maximum material virtual size, is the size generated by the collective effect of the maximum material size, MMS, of a feature of size and the geometrical tolerance form, orientation or location given for the derived feature of the same feature of size NOTE 1 Maximum material virtual size, MMVS, is a parameter for size used as a numerical value connected to MMVC.
PJ: Projected tolerance zone. A geometric tolerance zone which projects from an actual design features such as a hole MMR,Maximum material requirement; The identified requirement for a feature of size, defining a geometrical feature of the same type and of perfect form, with a given value for the intrinsic characteristic dimension equal to MMVS, which limits the non-ideal feature on the outside of the material.
This parameter is used to control the assembleability of the components. The minimum assembly clearance occurs when each of the mating componentsis at its maximum material size e. Assembly clearance are maximised when the sizes of the assembled features of size are at least material size e.
If the size of one mating part is less than its maximum material size, the indicated geometrical tolerance of the feature may be increased without endangering the assembly to the other part. This assembly function is controlled by the maximum material requirement.
The maximum metal requirement is that the component boundaries should not violate the maximum metal virtual condition of the perfect form at the size meeting the maximum metal requirement e. When the maximum metal condition symbol M in circle when used in the tolerance frame, it is indicated by a symbol placed after.
With maximum material requirement, the two requirements size and geometrical tolerance are transformed into one collective requirement. In the figure below the shaft is required to be perfectly straight at maximum metal condition. If the shaft was at its lower limit of size then it is acceptable that the shaft is allowed to be 0,5mm out in straightness.
In the figure below maximum metal requirement is with a 0,5mm allowance. The datum face B is positioned using the two datum circular areas B1 and B2. The datum surface C is positioned using the datum circular daturm surface C1. This condition applies to parts made of elastic or plastic materials or of thin flexible materials.
The free state condition of a part is when it is not restrained and subject only to the force of gravity. The distortion of such a part should be such that if will be brought within the specified tolerances for verification at assembly or by assembly using forces expected under the normal assembly conditions.
Drawings of non-rigid parts should include ;. An identification of the standard BS ISO in the notes section A note identifying the conditions providing the restraint in the assembled conditions when the drawing requirements apply Geometrical variations allowed in the free state with a modifying in the tolerance frame.
A note identifying the condition of the free state e. A crude example of how a free state geometrical tolerance is applied is provided in the figure below. The interpretation of this figure is that the tolerances followed by shall apply in the free state. The other tolerances apply in the assembled condition. Remember - the information on this site is for general information purposes only and while we endeavour to keep the information up to date and correct, we make no representations or warranties of any kind, express or implied, about its completeness, accuracy, reliability, suitability or availability.
Any reliance you place on such information is therefore strictly at your own risk. Roy Beardmore passed away on 9th March He is sadly missed.
This website, Roymech, has been an invaluable resource for engineers around the world and we hope to maintain this incredible legacy going forward. Have a question? Contact us. Introduction These notes attept to clarify the meanings of the supplimentary symbols used for geometric tolerancing. Maximum Material Requirement The minimum assembly clearance occurs when each of the mating componentsis at its maximum material size e.
When the maximum metal condition symbol M in circle when used in the tolerance frame, it is indicated by a symbol placed after - the tolerance value - the datum letter - or both With maximum material requirement, the two requirements size and geometrical tolerance are transformed into one collective requirement. The maximimum metal requirement is applied to holes in a similar way as shown below.
An example of the application of maximum material requirement to coaxiality is illustrated in the figure below Least Material Requirement The least material requirement shall be indicated by the specification modifier symbol. When the least metal requirement symbol is used in the tolerance frame, it is indicated by a symbol placed after - the tolerance value - the datum letter - or both This requirement is generally used to limit the least material situation e.
Theoretically exact dimensions The dimension determining the theoretically exact form, orientation or position respectively must not be toleranced. This is illustrated in the figure below Projected tolerance zones In some cases, the tolerance of orientation and position shall apply not to the feature itself but to the external projection of it.
This requirement is illustrated by the following simple example Common zone it is possible to apply a single tolerance zone to several separate features. Datum Targets When surfaces are identified as datum faces there is the problem that real surfaces vary significantly from ideally flat surfaces.
The figure below provides a crude example of a block with three datum faces to be identified and a hole which is provided with geometrical tolerances relative to the three datum faces The figure illustrates the representative drawing. Drawings of non-rigid parts should include ; An identification of the standard BS ISO in the notes section A note identifying the conditions providing the restraint in the assembled conditions when the drawing requirements apply Geometrical variations allowed in the free state with a modifying in the tolerance frame.
For access to document , on European-Standard-based drawing procedures Volvo Geometrical Tolerancing For access to document ,2e on European-Standard-based geometrical tolerancing Baseline Uncertainty in Geometric Tolerance Inspection Interesting downloadable paper Drawing Standards Downloadable Notes from Dartmouth U.
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