1、 Vernier caliper
(1) Use and construction of vernier caliper:
The caliper structure is mainly composed of two parts as shown in Figure 1-1, i.e. the movable cursor part a and the main ruler Part B. From the back, the cursor is a whole body. There is a spring plate between the cursor and the ruler body (not shown in the figure). Use the spring force of the spring plate to make the cursor close to the ruler body. There is a fastening screw on the upper part of the cursor, which can fix the cursor at any position on the ruler body. There are measuring claws on the ruler body and the cursor. The width of the groove and the inner diameter of the tube can be measured by the inner measuring claw, and the thickness of the part and the outer diameter of the tube can be measured by the outer measuring claw.
(2) Principle and use:
Take the vernier caliper of 50 minutes as an example
The Zui small scale of the main ruler of vernier caliper is 1mm,
There are 10 equal divisions on the vernier, the total length is 49mm, which is 1mm smaller than the scale on the main ruler, so the difference between each division on the vernier and Zui small division on the main ruler is 1 / 50 = 0.02mm, and the degree is 0.02mm.
When the equivalent claw is closed, the zero scale line of the cursor is aligned with the zero scale of the main ruler, and the indication is 0.
During measurement, hold the ruler body with the right hand, move the cursor with the thumb, and hold the object with the outer diameter (or inner diameter) to be measured with the left hand, so that the object to be measured is located between the outer measuring claws. When it is closely connected with the measuring claw, the reading can be made.
When reading, first take the zero scale line of the cursor as the standard and read the whole millimeter on the ruler, that is, the whole part in millimeter. Then look at the alignment of the scale lines on the cursor with the scale lines of the ruler body. If the sixth scale line is aligned with the scale lines of the ruler body, the decimal part is 0.6mm (if there is no exactly aligned line, take the Zui line close to the alignment for reading).
Vernier calipers do not require estimation. If there is no scale on the vernier that is aligned with the scale line of the main ruler, select a reading close to Zui, and the effective number should be aligned with the accuracy.
(3) Precautions for using vernier caliper:
① Before measurement, check the zero reading of vernier caliper to see whether the zero scale line of main and auxiliary ruler is aligned. If not, record the zero reading so as to correct the measured value.
② When the measured object is stuck, the tightness shall be proper, and the force shall not be too large. Pay attention to protect the cutting edge of vernier caliper.
③ When measuring the inner diameter of the cylinder, adjust the position of the knife edge so as to measure the diameter rather than the chord length.
2、 Screw micrometer
(1) Purpose and construction
The screw micrometer (also called micrometer) is a more precise tool to measure the length than vernier caliper. It can measure the length accurately to 0.01mm and the measuring range is several centimeters.
The structure of the screw micrometer is shown in the figure. The fixed scale of the small anvil of the screw micrometer is fixed on the frame, the knob, the fine-tuning knob are connected with the movable scale and the micrometer screw, and is sleeved on the fixed scale by the precise thread.
(2) Principle and use
The screw micrometer is made according to the principle of screw amplification, that is, the screw rotates once in the nut, and the screw moves forward or backward one pitch along the direction of the rotation axis. Therefore, the small distance along the axis direction can be indicated by the reading on the circumference. The pitch of the precision thread of the screw micrometer is 0.5mm, and the movable scale has 50 equally divided scales. The movable scale can rotate for one circle, and the micrometer screw can move forward or backward 0.5mm. Therefore, rotating each small scale is equivalent to 0.5/50 = 0.01mm when the micrometer screw moves forward or backward. It can be seen that each small division of movable scale represents 0.01mm, so the accuracy of screw micrometer can reach 0.01mm. It is also known as micrometer because it can read another digit and can read thousands of millimeters.
When the small anvil and the micro measuring screw are close together, if the zero point of the movable scale coincides with the zero point of the fixed scale, screw out the micro measuring screw, and make the surface of the small anvil and the micro measuring screw just contact the two ends of the length to be measured, then the distance that the micro measuring screw moves to the right is the measured length. The whole millimeter of this distance is read out on the fixed scale, and the decimal part is read out on the movable scale.
(3) The following points should be noted when using the screw micrometer:
① During measurement, when the micrometer screw is close to the object to be measured, stop using the knob, and use the fine adjustment knob instead to avoid excessive pressure, which can not only make the measurement results, but also protect the screw micrometer.
② When reading, pay attention to whether the half millimeter mark on the fixed scale has been exposed.
③ When reading, there is an estimated reading number in the thousandth position, which cannot be thrown away at will. Even if the zero point of the fixed scale is exactly aligned with a certain scale line of the movable scale, it should also be read as "0" on the thousandth position.
④ When the small anvil and the micrometer screw are close together, the zero point of the movable scale does not coincide with the zero point of the fixed scale, and there will be zero error, which should be corrected, that is, the zero error value should be removed from the reading of the last measured length.