Tolerance vs Allowance
In English, tolerance of a person is said to be his limit of patience. This capacity to tolerate is different in different people as in drug tolerance, alcohol tolerance or even religious tolerance. We can see that tolerance is seen as a virtue in human beings. However, the concept has a different meaning in science, especially engineering where tolerance is applied to dimensions. There is another concept of allowance that confuses students as it has similarities with tolerance. However, despite overlapping, there are differences between tolerance and allowance that will be talked about in this article.
In the engineering discipline, much importance is attached to the concept of tolerance. Metal parts are used in great numbers, in assemblies and manufacturing plants. These parts must fit each other comfortably. This is possible if they conform in size with each other. To fit with each other, metal parts need to have tolerance that allows them to compress or expand a bit. The range of tolerance of a metal or substance is based upon its physical and chemical properties.
If two components are required to be fit into each other in such a way that one has to be placed inside a hole in another, the difference in diameters of the two parts is kept normal for ease of fit while, sometimes the clearance is deliberately kept small, to allow for force to be used to fit. This fit is called force fit or press fit. Sometimes the difference in sizes is so small that heat may have to be used to fit the components together.
Metal parts and components are made in batches and when bought from the market have different batch numbers. This means there may be differences in dimensions that are not visible to the naked eye. This is where tolerance levels come handy as otherwise it may not be possible for two metal parts to fit together.
Allowance is a concept very similar to tolerance but is different in the sense that allowance refers to tolerance in dimension that is deliberately given to a metal during the process of manufacture and design. This is a planned deviation from the standard that is intended to allow for compensation should there be any unforeseen circumstances that interfere with the dimensions of the metal parts or components.
What is the difference between Tolerance and Allowance?
• In engineering or science, tolerance is the permissible limit or limits of variation in dimension or value or property.
• As metal parts are made in batches and used frequently in engineering applications, there needs to be a tolerance in dimensions to allow for easy fit of components.
• Allowance is similar in concept though it is a planned deviation from the ideal.
• Allowance still conforms to a specification that is the one set as tolerance but allows for a deliberate shift.