Go no go gauge (smooth limit gauge)

Go no go gauge is a special tool for inspection hole and shaft without scale. It can not measure the actual size of the workpiece, but can only measure whether the workpiece is within the specified limit size range, so as to judge whether the workpiece is qualified. It is simple and rapid to use it to test workpieces.

The working principle of the go no go gauge is to use the go end and stop end of the go no go gauge to check whether the size of the parts exceeds the maximum and minimum size respectively, so as to judge whether the inspected parts are qualified. The through end is manufactured according to the maximum physical size of the measured hole, that is, the minimum limit size of the hole, and the stop end is manufactured according to the minimum physical size of the measured hole, that is, the maximum limit size of the hole. When in use, when the through end of the go no go gauge passes through the tested hole, it means that the measured hole diameter is greater than the minimum limit size, and the stop end of the go no go gauge cannot plug into the tested hole, it means that the measured hole diameter is less than the maximum limit size, that is, it means that the size of the tested hole is within the specified limit size range, so this part is a qualified product. The go no go gauge used to check the shaft diameter is called ring gauge or snap gauge. The go end of the snap gauge is manufactured according to the maximum physical size of the measured shaft (i.e. the maximum limit size of the shaft), and the snap gauge is manufactured according to the minimum physical size of the measured shaft (i.e. the minimum limit size of the shaft). When in use, when the go end of the snap gauge passes through the shaft diameter smoothly, it means that the measured shaft diameter is smaller than the maximum limit size, and the stop end of the snap gauge cannot pass through the shaft diameter, It means that the diameter of the measured shaft is larger than the minimum limit size, that is, the size of the measured shaft is within the limit size range of your, and this part is a qualified product.

The code of the through end of the go no go gauge is t and the code of the stop end is Z. the go no go gauge is an easily worn part. Therefore, when in use, pay attention to handle it with care, do not insert it forcibly, and try to avoid collision, so as to cause the size of the go no go gauge to deteriorate and affect the accuracy of measurement. When not in use, it shall be cleaned, oiled and maintained, and placed in a special place to prevent corrosion and deformation

I. Basic Concepts

Smooth limit gauge is a special inspection tool without scale. It can not determine the actual size of the workpiece, but can only determine whether the workpiece size is within the range of limit size.

The smooth limit gauge of the inspection hole is called the plug gauge. The plug gauge generally has two ends, and one end is manufactured according to the maximum physical size of the measured hole (the minimum limit size of the hole), which is called the through gauge; The other end is manufactured according to the minimum physical size of the measured hole (the maximum limit size of the hole), which is called the stop gauge. Figure 2-5-22 shows the relationship between the diameter of the plug gauge and the hole diameter. The smooth limit gauge of the inspection shaft is called the ring gauge or caliper. Similarly, one end of the caliper is manufactured according to the maximum physical size of the measured shaft (the maximum limit size of the shaft), which is called the through gauge, The other end is manufactured according to the minimum physical dimension (the minimum limit dimension of the shaft) of the measured shaft, which is called the stop gauge. Fig. 2-5-23 shows the relationship between the caliper size and the shaft diameter. The through gauge and non-stop gauge must be used together during measurement. The hole or shaft is qualified only when the through gauge can pass through the measured hole or shaft and the non-stop gauge cannot pass through the measured hole or shaft.

The smooth limit gauge is used to inspect holes and shafts with basic dimensions up to 500mm tolerance grade it6-it16 specified in the national standard tolerance and fit gb1800-79. The gauge standard is formulated according to the principle of Taylor (i.e. the principle of limit dimension determination).

In actual production, it is very difficult or even impossible to adopt gauges that fully comply with Taylor’s principle. When it can be ensured that the shape error of the inspected workpiece does not affect the fitting property, the gauge deviating from Taylor principle is allowed to be used

When testing the workpiece with a standard gauge, in case of any dispute, the go no go gauge of the gauge block shall be equal to or close to the maximum / minimum physical size of the workpiece, or a quantifiable testing instrument shall be used.

According to Taylor’s principle, the through end of the gauge shall be made into a complete shape as far as possible, and the stop gauge shall be in point contact with the workpiece in theory. According to the size of the measured workpiece, the gauge type recommended by the national standard of smooth limit gauge and its application size range are as follows:

When the workpiece is inspected with a gauge conforming to the smoothness limit, if the go gauge can pass and the no go gauge cannot pass, the workpiece is qualified.

“Go gauge passing” means that the go gauge can enter the workpiece in any direction and pass the workpiece. “No go gauge passing” means that it cannot pass the workpiece. Strictly speaking, it should not only fail, but also cannot enter the workpiece. When the workpiece with deep or long hole is used according to practical experience, it is allowed to enter 1-2mm

There are clear provisions on the use of gauges in the world: 1) when the through-end plug gauge is operated by hand without great force, it shall be able to fully fit with the hole, and the whole length of the hole shall be inspected. When the stop plug gauge is operated by hand without using strong force, it shall not enter the hole. If possible, both ends of the hole should be inspected. 2) when the through-end clamp gauge is used to inspect the horizontally placed shaft, the weight of the gauge should be able to pass through the shaft. When the non full plug gauge is inspected, it should be inspected at no less than four positions along and around the shaft. 3) when the through-end ring gauge is operated by hand without applying great force, it should be able to pass through the full length of the shaft

When it is stipulated in the international standard that “great force is not used” rather than how much force is used, because there will always be a certain measuring force when using the gauge to inspect the workpiece. Because the gauge has no force measuring mechanism, it is difficult to unify the measuring force into a quantitative value in use, so the specific value is not clearly specified.

Operation method of the gauge: when using the through end of the plug gauge to inspect the workpiece, the handle of the plug gauge shall be held by hand. Generally, no pressure shall be applied. Under its own force, the plug gauge shall slide gently into the hole and pass through the full length of the hole, or a little force shall be added to gently send the plug gauge into the hole by hand

When using the stop end of the plug gauge to inspect the workpiece, strictly speaking, only the chamfered part is allowed to be placed on the edge of the empty mouth and cannot be plugged in, it is regarded as qualified. Even if only a small part of the end stop can be inserted into the hole, the hole shall be considered unqualified. However, in actual use, the stop end of the plug gauge with a depth of less than 10mm is allowed to enter less than 1mm, and the mouth with a depth of more than 10mm is allowed to enter 1-2mm