Tolerances on dimensions

BS2989 1992, Specification for continuously hot-dip zinc coated and iron-zinc alloy coated steel flat products tolerances on dimensions and shape ... 

Tight tolerances on dimensions should be specified only where absolutely necessary. Too many drawings show limits of sizes where other means of attaining desired results would be more constructive or the tolerances... 

Although hot-pressing is usually regarded as an expensive process and only simple shapes with a wide tolerance on dimensions can be made, it provides the only route for several valuable materials. Continuous hot-pressing methods have been developed for some magnetic ferrites and piezoelectric niobates. They olfer higher production rates but tool wear is very severe. 

Square bars, tolerances on dimensions and form NE A 50-703 ANSI H35.2... 

The interchangeability of joints is ensured by the use of a standard taper of 1 in 10 on the diameter (i.e., a cone of semi-angle 2° 51 45 ) and limited tolerances on the cone semi-angles and the dimensions of the joints. The specifications for joints in Great Britain and the U.S.A. differ. It will accordingly be necessary to treat each separately. 

Following the tolerance stack through the end assembly, the bobbin dimension of 22 mm from the outside face to the back face of the magnetic pole is analysed next. This characteristic dimension does not include the tolerance on the impact extruded pole. The pole is to be moulded into the bobbin and the pole face is considered to be part of a mould related dimension. The bobbin is injection moulded using 30% filled polybutylene terephthalate (PBT). The tolerance assigned to the bobbin dimension is 0.035 mm. 

In general, tolerance stack models are based on either the wor.st case or statistical approaches, including those given in the references above. The worst case model (see equation 3.1) assumes that each component dimension is at its maximum or minimum limit and that the sum of these equals the assembly tolerance (initially this model was presented in Chapter 2). The tolerance stack equations are given in terms of bilateral tolerances on each component dimension, which is a common format when analysing tolerances in practice. The worst case model is ... 

To determine the risk value A , look along the horizontal axis until the characteristic dimension is found, and at the same time, locate the adjusted tolerance on the vertical axis. Read off the A value in the zone at which these lines intersect on the map by interpolating as required between the zone bands, A = 1 to A = 9. 

Establishing the interface design parameters is easy enough, but forcing designers to establish acceptable tolerance on interface boundary conditions is difficult. Operating parameters need tolerance just as much as manufactured dimensions. 

An influence on dimensions and tolerances involves the coefficient of linear thermal expansion or contraction. This CLTE value has to be determined at the product s operating temperature (Chapter 2, THERMAL EXPANSION AND CONTRACTION) Plas tics can provide all extremes in CLTEs. As an... 

The factors that cause a gear to mesh tightly are (1) tolerance on concentricity of shaft hole with pitch diameter, (2) tolerance on center distance, (3) tolerance on quality, (4) coefficient of thermal expansion, and (5) change in dimensions due to moisture absorption, which is a consideration/detriment in some materials. The first three apply to gears of any material. Item 4, and in some cases Item 5, for plastic gears deserves special consideration. 

It is important to set close tolerances on the weir height, downcomer clearance, and plate flatness, to ensure an even flow of liquid across the plate. The tolerances specified will depend on the dimensions of the plate but will typically be about 3 mm. 

The first requirement is that the test piece should be dimensionally accurate but this is not dealt with in ISO 23529, the necessary tolerances and dimensions remaining a subject for the individual test method. The important dimensions can be conveniently checked on a cut test piece using a projection microscope, but the dimensions of the cut test piece will not necessarily be identical with the dimensions of the die because of the pressure of the blade deforming the rubber. In the majority of tests it is the test piece dimensions which are those specified. 

Codes and standards relevant to safety relief valves (SRVs) can vary quite considerably in format around the world, and many are sections within codes relevant to boilers or pressure-containing vessels. Some will only oudine performance requirements, tolerances and essential constructional detail, but give no guidance on dimensions, orifice sizes and so forth. Others will be related to installation and application. It is quite common within many markets to use several codes in conjunction with one another and it is not uncommon that specifications call for sections taken from several codes, which makes compliance by manufacturers complex and uneconomical. An overview of most common worldwide codes and standards is given in Appendix M. 

Customer expectations for service operate at two levels—desired and adequate. In other words, there is the ideal of what customers expect and the level of service that will satisfy them. Ideally, one would expect every airline flight to arrive and depart precisely on time, the attendants be personally solicitous, and luggage never be lost or damaged. Realistically, the customer personally may find a 15-minute delay, a courteous attendant, and a rare problem with luggage to be acceptable. Any level of service in the gap between ideal and adequate service is characterized as a zone of tolerance. The zone of tolerance for acceptable service varies based on the specific service dimension. The zone of tolerance for reliability on the filling of a prescription is exceedingly narrow. More than likely there is no zone of tolerance on this dimension. Conversely, the zone of acceptance for the appearance of a pharmacy for many customers is probably quite wide. More than likely, once a minimum standard for cleanliness is met, the customer may care little about how the pharmacy looks (Parasuraman, Berry, and Zeithaml, 1991). 

Tolerances on panel dimensions - length and width, squareness and thickness. 

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