|Measuring and Testing - Course: Technique for Manual Working of Materials. Trainees' Handbook of Lessons|
Testing tools (gauges) are sensitive instruments of surface hardened steel without any graduation. The measure is represented by their shape or size or setting.
Some testing tools have their type of measure engraved on them.
3.1. Size gauges
Size gauges are used to determine sizes or to check whether any dimensions of parts are within admissible limits.
The answer may be:
Yes - the size is within the admissible range.
No - the size is smaller than required.
No - the size is bigger than required.
If the answer is "no", it is to be decided whether (reworking) corrections of the part are possible.
Instrument with movable legs for outside and inside testing which are set to the size of the workpiece or setting of which is done by means of a measuring instrument before use.
Instrument which consists of several leaves of different thicknesses (0.05 to 0.1 mm increments) and is used to determine the size of narrow clearances by inserting a leaf into the clearance.
Drill and wire gauges:
Instruments with holes on a steel disk in 0.1 mm increments to quickly determine the diameter of drills or wires.
Square, standardized blocks, each representing a very precise measure of length (from 0.1 mm) .They are arranged in sets in boxes and are used for differential or comparative measurements.
Instruments representing the maximum and minimum limits of very small, standardized tolerance ranges (such as to the ISA system of tolerances and fits):
- Cylindrical limit plug gauge - for fitting inside diameters
1 "go" end (minimum size), 2 handle with designation of fit, 3 marking (red) of "not go" end, 4 "not go" end (maximum size)
- Limit screw plug gauge - for fitting female threads.
The "go" end (minimum diameter) must easily go into the bore, the "not go" end (maximum diameter, marked with red colour) must not go into the bore.
- Limit snap gauge - for fitting outside diameters
1 "go" end (maximum size), 2 gauge body with designation of fit, 3 marking (red) of "not go" end, 4 "not go" end (minimum size)
The "go" end (maximum diameter) must easily go over the work-piece, the "not go" end (minimum diameter, marked with red colour) must not slide over the workpiece,
- Ring thread gauge - for fitting male threads
When the ring can be screwed onto the thread, the thread is fitting!
(This does, however, not say whether the thread is possibly skew or dented).
What is the difference between measuring and testing tools?
What are the special features of limit gauges compared to simple size gauges?
What testing method is typical of the use of cylindrical limit plug gauges?
What are the results of testing by means of limit screw plug gauges and ring thread gauges?
3.2. Form gauges
Form gauges are used to determine whether the requirements as to flatness, squareness, roundness or other forms are met.
The light-gap testing method is applied:
Place the gauge against the workpiece and hold it against the light! The light gap between the gauge and workpiece must be evenly narrow!
(Form errors from 0.003 mm can be detected)
Instrument designed as steel straightedge (with straight reference faces) or as bevelled steel straightedge (with one knife edge) for flatness tests on finished surfaces.
Instrument designed as millwrights' steel square (with straight reference faces), back square (with straight reference faces and one reference face designed as stock support) or bevelled edge square (with one knife edge) for flatness tests of faces and angularity tests (mostly 90° degrees) of two faces or edges to each other.
Instruments for specific angles (60, 120, 55. 118 degrees).
Instruments consisting of one or more specifically radiused leaves (increment of radii 1 mm) for convex or concave radii.
Which testing method is typical of form gauges?
What is the difference between try squares and angle gauges?