A machine is formed by combining the different types of parts together. It runs continuously to give output, but due to continuous working, sometimes its parts get damaged. At that time, the stability with which the damaged parts get replaced by new ones is known as the interchangeability of parts. Interchangeability is a very important phenomenon as in this case, if the pare is not interchangeable then, one has to make new parts, which can replace the damaged parts. The whole process consumes much time and affects the production of plants or machines.
Therefore, it is essential that each and every part of the machine should be made very accurate so that whenever replacement of the worn-out part is needed, it can be replaced easily. Interchangeability of the parts depends upon the many factors such as limit, tolerance, and fit given between the mating parts.
So, in this chapter, we will study the factors on which interchangeability depends and its various related aspects. But firstly, we will start with the basic size and actual size of the job as they show the size of parts that are to be interchanged and the whole factors that affect the interchangeability.
Basic Size
Here, basic size refers to the size of a job on which, the limitation is permissible. e.g., If the dimensional representation of a job is given by 50 ± 0.02 mm, then the basic size will be 50 mm.
Actual Size
The actual size of a job is referred to as the job size obtained after the machining of a workpiece. If the size of a product (job) is within the limitation, which means the actual size is greater than the lower limit size and smaller than the upper limit size, then it will be passed.
If the actual size is lower than the lower limit size and greater than the upper limit size, then the job will be rejected. To assign and maintain the limitations and fits, there are many standard organizations as given below.
(i) International Standard Organisation (ISO)Â
(ii) British Standard Organisation (BSO)