Types of limit gauges and their uses

LIMIT GAUGES

. principle of Go and No-Go gauges

. the common types of limit gauges and their uses

. essential features of Go and No-Go gauges

Components manufactured using mass production methods are checked only to ensure that the sizes are within the prescribed limits. The  most economical method of checking such components is by using limit gauges. These gauges are used in inspection because they provide a quick means of checking.

Go and No-Go principle

The Go and No-Go principle of gauging is that the Go-end of the gauge must go into the feature of the component being checked and the No-Go end must not go into the same feature. The diemensions of the Go and No-Go ends of gauges  are  determined from the limits stated on the dimension of the component to be gauged. The diemension of the Go-end is equal to the minimum permissible dimension and that of the No-Go end is equal to the maximum permissible dimension.

Essential features

These gauges are easy to handle and are accurately finished. They  are generally finished to one tenth of the tolerance they are designed to control. For example, if the tolerance to be maintained is at0.02mm, then the gauge must be finished to within 0.02mm, of the required size.

These gauge must be resistant to wear, corrosion and expansion due to temparature. The plugs of the gauges are ground and lapped.

The Go-end is made longer than the 'No-Go' end for easy identification. Sometimes a groove is cut on the handle near the 'No-Go' end to distinguish it from the 'Go' end.

The diemensions of these gauges are usually stamped on them.

Types of cylindercal plug gauges

There are several types of cylindercal plug gauges

Duble ended  plug gauge

Progressive plug gauge

These plug gauges are used for checking the diameter of a straight hole. The Go-gauge checks the lower limit of the hole and the 'No-Go' gauge checks the upper  limit.

Plain ring gauges

These are used to check the outside diameter of the workpiece. Seperate gauges are used for checking Go and No-Go sizes. The No-Go gauge is identified by an annular groove, cut on the knurled surface.

Taper ring gauges

These gauges are used to check both the accuracy and the outside diameter of a taper. Ring gauges often have scribed lines or a step ground on the small end to indicate the Go and No-Go diemensions.

Thread plug gauges

Internal threads are checked with thread plug gauges of 'Go' and 'No-Go' variety which employ the same principle as the cylindercal plug gauges. The thread plug gauges check the form and dimensional accuracy of internal threads.

Thread ring gauges

These gauges are used to check the accuracy of an external thread. They check the form and the diemensional accuracy of external threads.

Snap gauges

Snap gauges are used as a quick means for checking sizes within certain limits by comparing the size of the parts with the opening of the gauge.

Adjustable caliper gauge

These gauges are generally C-shaped and are adjustable to the maximum and minimum limits of the part being checked. When in use, the work should slide into the Go anvil but not into the No-Go anvil. Snap gauges and adjustable caliper  gauges can be used for checking external sizes in any place along the length of a work.