Tolerancing of multiple chains
When a product is designed, two points of view must always be accommodated:
The manufacturer’s point of view: they want to be able to produce the parts according to a plan. The quality of production being measured by their ability to deliver parts that conform to the drawings.
The user’s point of view: they want to enjoy a problem-free product. Whether or not the parts conform to the drawings is unimportant to them. The most important thing is that the product has all the necessary functionality.
Obviously, the user’s point of view is the most important because it is the user that will judge the quality of the product in the end. However, when a part is produced it is only the characteristics which allow us to determine whether or not a part is conform. The art of tolerancing aims to reconcile these two points of view.
It is not generally one individual characteristic that determines the quality of a product, but the accumulation of several characteristics.
Let’s use the following example:
In this example, the product functions if the play between the red and orange parts is sufficient (if the play is not sufficient, the parts will jam and the product’s performance will deteriorate). However, this play is not measured; it is the result of the assembly of 4 parts (A, B, C and D) which are all controlled individually./p>
The objective of tolerancing is to recommend tolerance intervals for each part in order to guarantee correct functioning once the final product is assembled.
There are several types of tolerancing: