微米

A micrometer is another useful device for magnifying small measurements. In micrometer, the accurate screw and nut are used for measurement. The micrometers having good accuracy (about 0.01 mm), hence is used for most engineering precision work.

微米原理

• 微米适用于螺钉和螺母的原理。螺钉附接到同心圆柱或顶针，其圆周分为多个相等的部分。我们知道，当螺钉通过螺母通过一个旋转转动时，其轴向运动等于螺钉螺纹的间距。
• If I am pitch or lead of screw-in mm, each rotation of screw advances it in relation to the internal threads a distance equal to I mm. If the circumference of the concentric cylinder is divided into n equal divisions, movement (rotation) of a cylinder through one division indicates 1/n rotation of the screw or 1/n mm axial advance.
• In millimeter micrometer instruments the screw has a pitch (lead) of 0.5 mm and thimble has 50 divisions so that the least count of the micrometer is equal to 0.5/50 =mm. By reducing the pitch of the screw thread or by increasing the number of divisions on the thimble, the axial advance value per one circumferential division can be reduced and the accuracy of measurement can be increased.

See also:工程计量介绍 - 测量型

至少计数千分尺

至少计数千分尺= pitch of the spindle screw / no of division in the spindle

微米零件外：

The figure illustrates an outside micrometer. It is used to measure the outside diameter and length of small parts to an accuracy of 0.01mm. The main parts of anoutside caliper are:

1. U形钢框架
2. anvil & spindle
3. lock nut
4. sleeve or barrel
5. thimble
6. ratchet

1.U shaped steel frame

The outside micrometer has a U shaped or C shaped frame. It holds all the micrometer parts together. The gap of the frame permits the maximum diameter or length of the job to be measured. The frame is generally made of steel, cast iron, malleable cast iron, or light alloy. It is desirable that the frame of the micrometer be provided with conveniently placed finger grips of heat-insulating materials.

2.Anvil and spindle

The micrometer has a fixed anvil protruding 3mm from the left-hand side frame. The diameter of the anvil is the same as the diameter of the spindle. Another movable anvil is provided on the front of the spindle. The anvils are accuracy ground and lapped with its measuring faces flat and parallel to the spindle. These are also available with WC faces. The spindle is the movable measuring face with the anvil on the front side. The spindle engages with the nut. It should run freely and smoothly throughout the length of its travel. There should be no backlash between the spindle screw and nut. There should be a full engagement of nut& screw when the micrometer is at its full reading.

3.Locknut

• A lock nut is provided on the micrometer spindle as shown in fig, to lock it when the micrometer is at its correct reading.
• The design of the locknut is such that it有效地锁定主轴而不改变测量面之间的距离。因此，它保持完美的对齐中的主轴。

4.Sleeve or Barrel:

套筒沿其长度精确地分开，清晰​​地标记为0.5mm，其是主要规模。它是镀铬和可调节零settings.

5.Thimble:

The thimble can be moved over the barrel, it has 50 equal divisions around its circumference.

6.Ratchet:

• The ratchet is provided at the end of the thimble. It is used to assure accurate measurement and to prevent too much pressure from being applied to the micrometer.
• 当待测量的工作表面附近的主轴倾斜时，操作者使用棘轮螺钉更紧密。棘轮在此时自动滑倒correct (uniform) pressure is applied and prevents the application of too much pressure.

Range Of Micrometer :

千分尺通常具有25毫米的最大开口。它们的测量范围为0至25 mm，25至50毫米，125至150 mm，可达575至600毫米。

Procedure to take micrometer reading

Procedure for measuring dimensions with the help of micrometer

1. Select a micrometer with a desired range of measurement.
2.检查千分尺是否零误差。它可以通过接触砧座和主轴的脸来检查。顶针上的零应在桶（主刻度）上的参考线上与零一致，如图4所示。如果不会发生这种情况，则在剪辑中存在零误差，该摩擦表中必须占最终读数。

3.按住工件，尺寸在砧座和主轴之间测量，如图3所示。然后通过Rachet进行最终调整，并在JOCK螺母的帮助下锁定它。

4.现在，采取读取主尺度，假设主尺度读数为13毫米，如图4所示。采取与枪管上的参考线一致的顶针读数。第35个分区线与参考线重合。

总读数=主尺度读数+（L.C. x读取顶针）
= 13.5 + 0.01 x 35
= 13.850毫米

Precautions to be taken while using a micrometer:

1. The micrometer is available in various sizes and ranges, and the corresponding micrometer should be selected depending upon the size of the workpiece.
2.千分尺应清洁任何灰尘，主轴应自由移动。
3. Check and set the zero reading before measuring.
4. The workpiece whose dimension is to be measured must be held in the left hand and micrometer in the right hand.
5. Make sure that the dimension to be measured in parallel to the axis of the spindle and the anvil.
6. Always use the rachet for final adjustment and locknut for taking readings.
7. In case of measurement of diameter make sure that the anvil and spindle faces touch the maximum dimension only.

微米误差源

1. The faces of anvil and spindle may not be truly flat.
2.在某些或所有部分的砧座或轴的砧座或主轴上缺乏平行和平坦度。
3. The setting of zero reading may be inaccurate.
4. Inaccurate readings have shown by fractional divisions on the thimble.
5.在砧座和主轴的脸上磨损，并在主轴的螺纹中磨损。
6. Error due to too much pressure on the thimble or not using the ratchet.

Types of Micrometers

There is a number of different micrometers available for specific application and accuracy.
1. Outside micrometer
2.在微米内
3. Vernier micrometer
4. Depth micrometer
5. Bench micrometer
6. Digital micrometer
7.差动螺旋千分尺
8. Micrometer with dial gauge
9.螺纹剪影

Inside micrometer

• 内部千分尺用于测量工件的内部尺寸。图1.25显示内部千分尺，施工类似于外部千分尺。然而，内部千分尺没有U形框架和主轴。测量尖端由钳口构成，其面将面部硬化并研磨到半径。
• One one of the jaw is held stationary at the end and the second one moves by the rotation of the thimble. The locking arrangement is provided with a fixed jaw. Fig. 1.26 shows another inside micrometer is used for a larger internal dimension. It consists of two anvils, sleeve, thimble, rachet, stop, and extension rods.

• The range of this micrometer is 50 mm to 210 mm. however, the range can be increased by anyone extension rod provided with it. This micrometer has no frame and spindle. The measuring points are at Extreme ends provided with anvils. The axial movement of endpoints is taken place by thimble rotation about the barrel axis.
• A series of extension rods are provided in order to obtain a wide measuring range. Before taking the measurement, the approximate internal dimension of a workpiece (whose dimension is to be measured by inside micrometer) is measured by a scale.
• The extension rod is then selected to the nearest one and inserted in a micrometer head.
• 然后,千分尺检查零错误智慧h the help of a standard-sized specimen whose internal dimension is known. The micrometer is then adjusted at a dimension slightly smaller than the internal (bore) diameter of the workpiece.
• 然后将微米头精细地保持在孔上，如图2所示。通过移动顶针调节其他接触表面直至感测正确的手感。然后除去千分尺并拍摄读数。延伸杆和套环的长度被添加到千分尺读取中。

Vernier micrometer

• 为了提高精度，vernier原理也适用于外部千分尺。这种类型的千分尺可以读取0.001mm长度。
• The vernier micrometer as shown in Fig.consists of three scales as follows:

1. The main scale is graduated on the barrel with two sets of division marks. The set below the reference line reads in mm and set above the line reads in 1/2 mm.
2. A thimble scale is graduated on the thimble with 50 equal divisions. Each small division of thimble represents 1/50 of a minimum division of the main scale. The main scale minimum division value is 1/2 mm.
3.枪管标记游标。枪管有10个部门，相当于顶针的9个部门。因此，游标标度的一个划分等于9 / 10thatofthimble。但是顶针的一个分裂等于0.01 mm。因此，vernier标度上的一个划分等于

Least count of vernier micrometer

L.C. = Value of smallest division on thimble- Value of smallest division on the vernier scale.
= 0.01 – 0.009
= 0.001毫米
因此，游标千分尺的精度为0.001mm。

Reading the vernier micrometer:

Main scale reading= 11.5 mm

顶针读书
= No. of thimble division coinciding with reference line x L.C. of a thimble
= 12 x 0.01
= 0.12毫米
第四个游标缩放线与顶针的分裂一致

Hence, vernier reading
=No. of vernier division coinciding with thimble scale x L.C. of vernier
= 6 x 0.001
= 0.006毫米
Total reading= 11.5 + 0.12 + 0.006
= 11.626 mm

If vernier line coincident with the reference line is 0, then no vernier reading added to the final reading.

Depth micrometer

• Depth micrometer (micrometer depth gauge) is used to measure the depth of holes, slots and recessed areas.
• 它由底座（测量面）组成，该基部（测量面）固定在筒和测量主轴上，该主轴连接，如图2所示。主轴的轴向运动通过顶针的旋转进行。

• The measurement is made between the end face of the spindle and the measuring face of the base. As spindle moves away from the base, the measurement increases due to scales on the barrel are reversed from the normal.
• The scale indicates zero when spindle flush with the face and maximum when the spindle is fully extended from the base Fig.shows the use of depth micrometer.
• 主尺度读数是17.顶针与参考线匹配的第14行。因此，顶针读数是
  Total reading= 17 + 0.14 = 17.14 mm
• The depth micrometer is available in ranges 0 -25 mm or0-50 mm. The range can be increased up to 0-90 mm by using extension rods in steps of 25 mm. The extension rod can easily be inserted by removing the spindle cap.

Differential screw micrometer

• Differential screw micrometer uses differential screw principle and hence the accuracy of -this micrometer is increased compared to an ordinary micrometer.
• In this micrometer, the screw has two types of pitches as shown in Fig., one smaller and other larger, instead of one uniform pitch as in ordinary micrometer.

• Both the screws are right-handed and the screws are so arranged that the rotation of thimble, one screw. Moves forward and other moves backward. The anvil is not attached to the thimble, but it slides inside the barrel.
• The smaller screw nut is fixed in the anvil while larger screw nut fixed with a barrel, hence screw rotates with the thimble. In the case of a metric micrometer, the normally employed pitch for the screws is 0.4 mm and 0.5 mm.
• Therefore, one revolution of the thimble, the measuring anvil will advance by an amount equal to 0.5-0.4 = 0.1 mm. The thimble circumference is graduated in 100 equal divisions. Hence anvil moves in an axial direction by mm corresponding one division of thimble this micrometer has a smaller range due to small total axial movement (differential axial movement) of the spindle.

Digital micrometer

• 作为千分尺和vernier的机械测量装置适用于在0.001mm内进行准确的测量。该装置便宜，轻巧，紧凑，相对粗糙。
• But when greater accuracy of measurement is desired, these mechanical devices are inadequate. In the case of digital or electronic instruments, measuring instruments having an electronic digital readout has become common in the industrial measuring instrument in order to get superior precision and ease of reading provided by the electronic digital readout.

• A digital micrometer consists of the frame, anvil, spindle, locknut, barrel, thimble, ratchet, LCD display, and ON/OFF ZERO key as shown in Fig. It has incorporated a digital readout into the structure of the micrometer’s body.
• The digital readout is integrated with a rotary encoder that is capable of reading the axial displacement of a spindle which rotates as a thimble is rotated.
• The digital micrometers are available in a large number of different sizes, normally 0-25 mm, 25-50 mm, 50- 75 mm, and 75-100 mm. They are used to measure length, diameter, or thickness.