Limit Gauges – Application , Advantages and Disadvantages
Introduction to Limit Gauges:
“Limit gauging is a method of checking dimensions in which a fixed gauge is applied to the work in order to determine whether a given component lies within its limits.”
Gauges are inspection tools of rigid design, without a scale, which used to check the dimensions of manufactured components.
Gauges do not indicate the actual value of the dimensions of the component. They are only used to check whether the inspected part has been made within the specified limits.
Thus, a limit gauge, unlike a conventional measuring tool, simply determines whether, the part is inside or outside the tolerance zone. The gauge neither measures a value of dimensions, nor shows the value of error evolved in the component. It simply checks that part is correct or not.
These are also called „go‟ and „no go‟ gauges. These are made to the limit sizes of the work to be measured. One of the sides or ends of the gauge is made to correspond to maximum and the other end to the minimum permissible size. The function of limit gauges is to determine whether the actual dimensions of the work are within or outside the specified limits. A limit gauge may be either double end or progressive. A double end gauge has the „go‟ member at one end and „no go‟ member at the other end. The „go‟ member must pass into or over an acceptable piece but the „no go‟ member should not. The progressive gauge has „no go‟ members next to each other and is applied to a workpiece with one movement. Some gauges are fixed for only one set of limits and are said to be solid gauges. Others are adjustable for various ranges.
Need of Limit Gauges:
There are two methods to ensure whether the components being produced on the shop floor are as per the pre-decided specifications or not.
(i) Measurement by measuring instruments.
(ii) Limit Gauging by fixed design limit gauges.
Obviously, measurement is the best method, but is not practical to check every dimension on each manufactured part. On the other hand, Limit gauging is faster, easier, and does not required skill inspector.
Also, accuracy of component greatly reflects itself in the cost of the product. To achieve a greater accuracy than necessary, it makes the project uneconomical. Thus, in repetition work it is not possible to check dimensions with the precision instruments like vernier, micrometer etc. This conventional measurement requires skilled or semiskilled workers.
Hence, in mass production where inter changeability is to be maintained at relatively low cost, the dimensional tolerance (high and low limits) are controlled by the limit gauges.
Advantages of Limit Gauges:
1. Quicker Inspection Method:
It is quicker than direct measurement. The time to inspect on shop-floor is minimized.
2. Used In-Mass Production:
Limit gauges are conveniently used in mass production for checking and controlling various dimensions.
3. Ensure Interchangeability:
A Limit gauge ensures interchangeability and hence components can be assembled without difficulty.
4. Need Semiskilled Operator:
Limit gauges can easily be used by semi-skilled operators.
5. Check both Linear and Geometric Features:
A proper designed limits gauge can check both linear and geometric features simultaneously.
Limit gauges are economical in their own cost as well as in inspection cost.
Limitations or Disadvantages of Limit Gauges:
1. Do not Indicate Exact Size:
Limit gauges do not indicate exact size of the component. They only indicated whether the component is within the tolerance zone or not.
2. Errors due to Wear:
Limit gauges are subjected to errors due to wear of gauges during use.
3. Difficulty in Checking of Finer Tolerance:
It is generally uneconomical to manufacture a limit gauge with 0-0.0013 mm tolerance, to check the work tolerance of about 0.013mm. Such fine limit gauges are also difficult to use in shop-floor, due to wear.
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