Interchange Ability

Interchangeability

Interchangeable parts are components of any device designed to specifications which insure that they will fit within any device of the same type. This streamlines the manufacturing process, since all pieces are guaranteed to fit with all others,

and it similarly creates the opportunity for replacement parts. In the U.S., Eli Whitney saw the potential benefit of developing "interchangeable parts" for the firearms of the United States military, and thus, around 1798, he built ten guns, all containing the same exact parts and mechanisms, and disassembled them before the United States Congress. He placed the parts in a large mixed pile and, with help, reassembled all of the weapons right in front of Congress And Engineers started to use Geometric Dimensioning and Tolerancing in the Engineering Drawing to tell the Machinist. Hey

look this is the actual dimension and you are allowed to attain the finished component dimension plus or minus tolerance value. This makes job easy for Machinist to work with machines and make cost effective products. Interchangeability of manufactured parts is a critical element of present day production. The production of closely mating parts, although theoretically possible, is economically unfeasible. For this reason, the engineer, designer or drafter specifies an allowable

deviation (tolerance) decimal limits.

between

The definition of a Tolerance, per ASME Y14.5.5M-1994, is the total amount a specific dimension is permitted to vary. For instance, a dimension shown as 1.498” to 1.502” means that it may be 1.498” or 1.502” or anywhere between these dimensions. Since greater accuracy costs money, you would not callout the tightest possible tolerance, but instead would callout as generous a tolerance as possible. Important Terms Definition:

Maximum Material Condition (MMC) – Is the condition where a feature of a finished part contains the maximum amount of material. That is, the largest shaft or smallest hole. See Example 1. Least Material Condition (LMC) - Is the condition where a feature of a finished part contains the least amount of material. That is, the smallest shaft or the largest hole. See Example 1.

Nominal Size – Approximate size used for the purpose of identification such as stock material. Basic Size – Is the theoretical exact size from which limits of size are determined by the application of allowances and tolerances. Tolerance – The total amount by which a given dimension may vary or the difference between the limits.

Limits – The extreme maximum and minimum sizes specified by a toleranced dimension.