35 MICROMETER SCREW GAUGE Micrometer screw gauge or micrometer caliper is a

35 micrometer screw gauge micrometer screw gauge or

This preview shows page 23 - 26 out of 33 pages.

3.5 MICROMETER SCREW GAUGE Micrometer screw gauge (or micrometer caliper) is a fine precision instrument or device used for measuring length of an object which is more precise than a ruler and vernier caliper. Ihis is because a micrometer screw gauge has the smallest scale of 0.01 mm. The device is widely used in mechanical engineering for measuring small diameter, thickness, or angles to a high degree of accuracy
Image of page 23
24 Fig. 2.4.1 micrometer screw gauge (outside micrometer) 2.4.2 Basic types of micrometers ° Outside micrometer (aka micrometer caliper), typically used to measure wires, spheres, shafts and blocks. One good example is the one shown in fig 2.4.1 ° Inside micrometer , used to measure the diameter of holes. ° Depth micrometer , measures depths of slots and steps 2.4.3 MICROMETER PARTS With reference to figure 2.4.1, the parts of a micrometer are defined as follows; Frame: This is a C-shaped body that holds the anvil and barrel in constant relation to each other. It is thick because it needs to minimize flexion, expansion, and contraction, which would distort the measurement. The frame is heavy and consequently has a high thermal mass, to prevent substantial heating up by the holding hand/fingers. It is often covered by insulating plastic plates which further reduce heat transference. This is because if you hold the frame long enough so that it heats up by 10°C, then the increase in length of any 10 cm linear piece of steel is of magnitude 1/100 mm. For micrometers this is their typical accuracy range. Micrometers typically have a specified temperature at which the measurement is correct (often 20°C [68°F], which is generally considered "room temperature " in a room with HVAC ). Tool rooms are generally kept at 20°C [68°F]. Anvil: The shiny part that the spindle moves toward, and that the sample rests against. Sleeve / barrel / stock: The stationary round part with the linear scale on it. Sometimes it has vernier markings. Lock nut / lock-ring / thimble lock: The knurled part (or lever) that one can tighten to hold the spindle stationary, such as when momentarily holding a measurement. Screw (not shown in the diagram): The heart of the micrometer, it is inside the barrel. This forms a very common method for measuring instruments, and is based on the thread principle. In effect,
Image of page 24
25 as a thread is turned, a large motion on the outside of the thread will result in a very small advance in the position of the thread Spindle: The shiny cylindrical part that the thimble causes to move toward the anvil. Thimble: The part that one's thumb turns or rotates and it has graduated markings. Ratchet stop: Device on end of handle that limits applied pressure by slipping at a calibrated torque. Inch system micrometer Fig 3.5a Micrometer thimble showing 0.276 inch The spindle of an inch-system micrometer has 40 threads per inch, so that one turn moves the spindle axially 0.025 inch (1 ÷ 40 = 0.025), equal to the distance between two graduations on the frame. The 25 graduations on the thimble allow the 0.025 inch to be further divided, so that turning the thimble through one division moves the spindle axially 0.001 inch (0.025 ÷ 25 = 0.001). Thus, the reading is given by the number of whole divisions that are visible on the scale
Image of page 25
Image of page 26

You've reached the end of your free preview.

Want to read all 33 pages?

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Stuck? We have tutors online 24/7 who can help you get unstuck.
A+ icon
Ask Expert Tutors You can ask You can ask You can ask (will expire )
Answers in as fast as 15 minutes
A+ icon
Ask Expert Tutors