Measuring Instruments Commonly Used In The Machining Workshop

Classification Of Measuring Instruments

A measuring instrument is an instrument with a fixed form, which is used to reproduce or provide one or more known values. The measuring tools can be divided into the following categories according to their purposes:

1. Single value measuring tool

The measuring tool can only reflect a single measurement value. It can be used to calibrate and adjust other measuring instruments or as a standard quantity for direct comparison with the measured, such as gauge block, angle gauge block, etc.

2. Multivalued measuring tool

It can reflect a group of measuring tools of the same kind. It can also calibrate and adjust other measuring instruments or directly compare them with the measured ones as standard quantities, such as linear ruler.

3. Special measuring tools

A measuring tool specially used to check a specific parameter. Common ones are: the smooth limit gauge for testing smooth cylindrical holes or shafts, the thread gauge for judging the qualification of internal threads or external threads, the inspection template for judging the qualification of surface profiles with complex shapes, and the functional gauge for testing assembly accuracy by simulating assembly pass through, etc.

4. Universal measuring tools

In China, measuring instruments with simple structures are customarily called universal measuring tools. Such as vernier caliper, outside micrometer, dial indicator, etc.

Hardness Tester Measurement

Technical Performance Indexes Of Measuring Instruments

1. Nominal value of measuring tool

The quantity value marked on the measuring tool to indicate its characteristics or guide its use. Such as the size marked on the gauge block, the size marked on the scriber, and the angle marked on the angle gauge block.

2. Graduation value

The difference between the values represented by two adjacent graduation lines (minimum unit measurement value) on the scale of the measuring instrument. If the difference between the values represented by the two adjacent graduation lines on the differential cylinder of an outside micrometer is 0.01mm, the graduation value of the measuring instrument is 0.01mm. The graduation value is the minimum unit value that can be directly read out by a measuring instrument, which reflects the reading accuracy and the measurement accuracy of the measuring instrument.

3. Measuring range

Within the allowable uncertainty, the range from the lower limit value to the upper limit value of the measured value that can be measured by the measuring instrument. For example, the measuring range of the outside micrometer is 0-25mm, 25-50mm, etc., and the measuring range of the mechanical comparator is 0-180mm.

4. Measuring force

In the process of contact measurement, the contact pressure between the measuring head of the measuring instrument and the measured surface. Too much measuring force will cause elastic deformation, and too little measuring force will affect contact stability.

5. Indication error

The difference between the indicated value of the measuring instrument and the measured true value. The indication error is a comprehensive reflection of various errors of the measuring instrument itself. Therefore, the indication error is different at different working points within the instrument indication range. Generally, gauge blocks or other measuring standards with appropriate accuracy can be used to verify the indication error of measuring instruments.

Selection Of Measuring Tools

Before each measurement, measuring tools shall be selected according to the special characteristics of the parts to be measured. For example, calipers, height gauges, micrometers and depth gauges can be selected for length, width, height, depth, outer diameter, segment difference, etc. Micrometer and caliper can be selected for shaft diameter. Plug gauge, block gauge and feeler gauge can be selected for holes and grooves; The right angle ruler shall be selected for measuring the right angle of parts. R gauge is selected for measuring R value. The third dimension and anime can be selected when the measuring fit tolerance is small, the precision is high or the geometric tolerance is required to be calculated; Hardness tester shall be used to measure steel hardness.

1. Application of caliper

Calipers can measure the inner diameter, outer diameter, length, width, thickness, segment difference, height and depth of objects. Calipers are the most commonly used and convenient measuring tools, which are used most frequently on the processing site.

Digital caliper: resolution 0.01mm, used for size measurement with small fit tolerance (high precision).

Meter card: resolution 0.02mm, used for regular size measurement.

Vernier caliper: resolution 0.02mm, used for rough machining measurement.

2. Application of micrometer

Before using the micrometer, first remove the dust and dirt with clean white paper (use the micrometer to measure the contact surface and screw surface to clamp the white paper and then pull it out naturally, repeat 2-3 times), then twist the knob to measure the quick contact between the contact surface and screw surface. When the contact surface and screw surface are in full contact, use fine adjustment. When both sides are in full contact, adjust the zero point after base note, and then the measurement can be carried out.

3. Application of height gauge

The height gauge is mainly used to measure the height, depth, flatness, perpendicularity, concentricity, coaxiality, surface vibration, tooth vibration, depth and height. When measuring, first check whether the measuring head and all connecting parts are loose.

4. Application of feeler gauge

The feeler gauge is applicable to the measurement of flatness, bending and straightness

5. Application of plug gauge (rod needle):

It is applicable to measuring the inner diameter, groove width and clearance of holes.

6. Precision measuring instrument: Quadratic element measure.

Quadratic element measure is a non-contact measuring instrument with high performance and high precision. The sensing element of the measuring instrument does not directly contact the surface of the measured part, so there is no measuring force under mechanical action. Quadratic element measure transmits the captured image to the data acquisition card of the computer through the data line through projection, and then the software images on the computer display; It can measure various geometric elements (points, lines, circles, arcs, ellipses, rectangles), distances, angles, intersections, geometric tolerances (roundness, straightness, parallelism, perpendicularity, inclination, position, concentricity, symmetry) on parts, and can also export 2D profiles to CAD. Not only the contour of the workpiece can be observed, but also the surface shape of the opaque workpiece can be measured.

7.Precision measuring instrument: Coordinate Measuring Machining (CMM)

The characteristics of the Coordinate Measuring Machining are high precision ( μ M), omnipotence (can replace a variety of length measuring instruments), can be used to measure geometric elements (in addition to the elements that can be measured by the anime element, it can also measure cylinders and cones), form and position tolerance (in addition to the form and position tolerance that can be measured by the anime element, it also includes cylindricity, flatness, line profile, surface profile, coaxiality), complex surfaces, as long as the CMM probe can reach the place, it can measure its geometric size, mutual position and surface profile, and complete data processing with the help of computers. With its high precision, high flexibility and excellent digital ability, it has become an important means and effective tool for modern mold processing and manufacturing and quality assurance.

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