These may be used as reference standards for transferring the dimension of the unit of length from the primary standard to gauge blocks of lower accuracy and for the verification and graduation of measuring apparatus. These are high carbon steel hardened, ground and lapped rectangular blocks, having cross sectional area 0f 30 mm 10mm. Their opposite faces are flat, parallel and are accurately the stated distance apart. The opposite faces are of such a high degree of surface finish, that when the blocks are pressed together with a slight twist by hand, they will wring together. They will remain firmly attached to each other. They are supplied in sets of 112 pieces down to 32 pieces. Due to properties of slip gauges, they are built up by, wringing into combination which gives size, varying by steps of 0.01 mm and the overall accuracy is of the order of 0.00025mm. Slip gauges with three basic forms are commonly found, these are rectangular, square with center hole, and square without center hole.
Wringing or Sliding is nothing but combining the faces of slip gauges one over the other. Due to adhesion property of slip gauges, they will stick together. This is because of very high degree of surface finish of the measuring faces.
Classification of Slip Gauges
Slip gauges are classified into various types according to their use as follows:
1) Grade 2
2) Grade 1
3) Grade 0
4) Grade 00
5) Calibration grade.
1) Grade 2:
It is a workshop grade slip gauges used for setting tools, cutters and checking dimensions roughly.
2) Grade 1:
The grade I is used for precise work in tool rooms.
3) Grade 0:
It is used as inspection grade of slip gauges mainly by inspection department.
4) Grade 00:
Grade 00 mainly used in high precision works in the form of error detection in instruments.
5) Calibration grade:
The actual size of the slip gauge is calibrated on a chart supplied by the manufactures.
Manufacture of Slip Gauges
The following additional operations are carried out to obtain the necessary qualities in slip gauges during manufacture.
i. First the approximate size of slip gauges is done by preliminary operations.
ii. The blocks are hardened and wear resistant by a special heat treatment process.
iii. To stabilize the whole life of blocks, seasoning process is done.
iv. The approximate required dimension is done by a final grinding process..
v. To get the exact size of slip gauges, lapping operation is done.
vi.Comparison is made with grand master sets.
Slip Gauges accessories
The application slip gauges can be increased by providing accessories to the slip gauges. The various accessories are
¬∑ Measuring jaw
¬∑ Scriber and Centre point.
¬∑ Holder and base
1. Measuring jaw:
It is available in two designs specially made for internal and external features.
2. Scriber and Centre point:
It is mainly formed for marking purpose.
3. Holder and base:
Holder is nothing but a holding device used to hold combination of slip gauges. Base in designed for mounting the holder rigidly on its top surface.