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Gear and Screw measurement
This document provides a comprehensive overview of screw thread measurements, including definitions, types of threads, and key terminology. It also discusses various methods for effective diameter measurement such as the two-wire and three-wire methods, as well as details about gears, gear measurement, and the functioning of tools like coordinate measuring machines and optical projectors. Overall, it serves as a guide to understanding measurement techniques in mechanical engineering.
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Gear and Screw measurement
- 1. www.company.com MODULE NO –3 10- 12 Marks Company LOGO PREPARED BY, Afaqahmed M J , AIKTC Prof. Afaqahmed (c) Copyright
- 2. www.company.com Company LOGO 1. SCREW THREADMEASUREMENT Prof. Afaqahmed (c) Copyright
- 3. www.company.com Company LOGO Screw thread-definition A screwthread is the helical ridge produced by forming a continuous helical groove of uniform section on the external or internal surface of a cylinder or a cone. A screw thread is a ridge wrapped around a cylinder or cone in the form of a helix, with the former being called a straight thread and the latter called a tapered thread. The helical groove opened to internal and external surface Prof. Afaqahmed (c) Copyright
- 4. www.company.com Company LOGO Types of thread 1.External thread: A thread formed on outside of a work piece is known as external thread. Example: on bolts or studs etc. 2. Internal thread: A thread formed on inside of a work piece is known as internal thread. Example: on a nut or female screw gauge. Prof. Afaqahmed (c) Copyright
- 5. www.company.com Company LOGO TERMINOLOGY OF SCREW THREAD Prof.Afaqahmed (c) Copyright
- 6. www.company.com Company LOGO Screw Thread terminology 1.Pitch: The distance from a point on a screw thread to a corresponding point on the next thread measured parallel to the axis. 2. Lead :The distance a screw thread advances in one turn. For a single start threads, lead = pitch, For double start, lead = 2 x pitch, & so on. 3. Thread Form: The cross –section of thread cut by a plane containing the axis. 4. Major Diameter: This is the diameter of an imaginary cylinder, coaxial with the screw, which just touches the crests of an external thread or roots o f an internal threads. It is also called as ‘Nominal diameter Prof. Afaqahmed (c) Copyright
- 7. www.company.com Company LOGO 5. Minor diameter:This is the diameter of an imaginary cylinder, co-axial with the screw which just touches the roots of an external thread or the crest of an internal thread. This is also referred to as ‘root’ or ‘core diameter’. 6. Effective diameter or Pitch diameter: It is the diameter of an imaginary cylinder coaxial with the axis of the thread and intersects the flanks of the thread such that width of the threads & width of spaces between threads are equal. 7. Flank: It is the Thread surface that connects crest with root. 8. Depth of thread: It is the distance between crest and root measured perpendicular to axis of screw. Prof. Afaqahmed (c) Copyright
- 8. www.company.com Company LOGO 9. Angle ofthread: Included angle between sides of thread measured in axial plane. 10. Helix angle: Angle that the thread makes with plane perpendicular to thread axis. 11. Flank angle: It is half the included angle of the thread. 12. Addendum: It is the distance between the crest and the pitch line measured perpendicular to axis of the screw. 13. Dedendum: It is the distance between the pitch line & the root measured perpendicular to axis of the screw. Prof. Afaqahmed (c) Copyright
- 9. www.company.com Company LOGO Floating Carriage threadMeasurement Prof. Afaqahmed (c) Copyright
- 10. www.company.com Company LOGO 1. It consistsof three main units. A base casting carries a pair of centres, on which the threaded work-piece is mounted. Another carriage is mounted on it and is exactly at 90° to it. 2. On this is provided another carriage capable of moving towards the centres. On this carriage one head having a large thimble enabling reading upto 0.002 mm is provided. 3. Thus the micrometer elements are exactly perpendicular to the axis of the centres as the two carriages are located perpendicular to each other. 4. On the fixed carriage the centres are supported in two brackets fitted on either end. The distance between the two centres can be adjusted depending upon the length of tie threaded job. 5. job is fitted between the centres the second carriage is adjusted in correct position to take measurements and is located in position, The third carriage is then moved till the Fiducial indicator is against the set point. Construction & Working Prof. Afaqahmed (c) Copyright
- 11. www.company.com Company LOGO 6. The uppercarriage is free to float on balls and enables micrometer readings to be taken on a diameter without restraint. Prof. Afaqahmed (c) Copyright
- 12. www.company.com Company LOGO Effective Diameter Measurement 1.Two Wire Method Prof. Afaqahmed (c) Copyright
- 13. www.company.com Company LOGO Working 1. Place twowires / rods of identical diameter between the flanks of the thread 2. This method can only be carried out on diameter measuring machine. 3. Axis of the micrometer is maintained @ 90 degree to the axis of screw thread. 4. Micrometer is attached with the wires which shows the readings 5. Effective Diameter is calculated as E = Effective Diameter E = T + P Where T = Dimension under the wires = M – 2d M = Dimension over the wires d = Diameter of each wire P = Value which depend on Dia & Pitch P = 0.9605 p – 1.1657 d (Whitworth Thread) P = 0.866 p – d (Metric thread) Prof. Afaqahmed (c) Copyright
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- 15. www.company.com Company LOGO Effective Diameter Measurement 2.Three Wire Method Prof. Afaqahmed (c) Copyright
- 16. www.company.com Company LOGO Working 1. Most accuratemethod to measure effective diameter 2. Three wires of known diameters are used : one on one side & two on other side 3. This method is precisely aligned with anvil of micrometer 4. Wires are either held in hand or hung from a stand to get adjusted themselves under micrometer pressure. Calculations to find out effective Dia. 1. Whitworth Thread M = D + 3.1657 d – 1.6 p Where D = Outside dia 2. Metric thread M = D + 3d – 1.5155 p 4. By finding the value of M we can find out E by knowing d. Prof. Afaqahmed (c) Copyright
- 17. www.company.com Company LOGO VIDEO OF THREEWIRE METHOD Prof. Afaqahmed (c) Copyright
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- 19. Folie 18 a1 aafaq;18.02.2016 Prof. Afaqahmed (c) Copyright
- 20. www.company.com Company LOGO What is agear ? A gear is a wheel with teeth that mesh together with other gears. Gears change the : • Speed • Torque (rot. force) • Direction of rotating axles. Prof. Afaqahmed (c) Copyright
- 21. www.company.com Purpose : To transmitrotary motion and force. Gears are used in groups of two or more. A group of gears is called a gear train. The gears in a train are arranged so that their teeth closely interlock or mesh. The teeth on meshing gears are the same size so that they are of equal strength. The spacing of the teeth is the same on each gear. Prof. Afaqahmed (c) Copyright
- 22. www.company.com Company LOGO TYPES OF GEARS 1.Accordingto the position of axes of the shafts. a. Parallel 1.Spur Gear 2.Helical Gear 3.Rack and Pinion b. Intersecting Bevel Gear c. Non-intersecting and Non-parallel worm and worm gears Prof. Afaqahmed (c) Copyright
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- 24. www.company.com Company LOGO PARKINSON’S GEAR TESTER Prof.Afaqahmed (c) Copyright
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- 26. www.company.com Company LOGO This machine, developedby James Parkinson, is popularly used for testing of spur gears, in pair. The principle of this device is to mount a standard gear on a fixed vertical spindle and the gear to be tested on another similar spindle mounted on a similar spindle mounted on a sliding carriage, maintaining the gears in mesh by spring pressure. Movements of the sliding carriage as the gears are rotated and indicated by a dial indicator, and these variations are a measure of any irregularities in the gear under test , alternatively a recorder can be fitted ,in the form of a waxed circular chart and records made of the gear variation in accuracy of mesh. Prof. Afaqahmed (c) Copyright
- 27. www.company.com Company LOGO When the waxedpaper recorder is fitted, the chart makes a revolution for each one of the gears mounted on the sliding carriage. As the chart moves and rotates, the line traced records the movements of floating carriage. A circle is drawn at the same time as the record as shown in figure. METHOD OF MEASUREMENT Prof. Afaqahmed (c) Copyright
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- 29. www.company.com Company LOGO TOOL MAKER’S MICROSCOPE Prof.Afaqahmed (c) Copyright
- 30. www.company.com Prof. Afaqahmed (c)Copyright
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- 32. www.company.com Company LOGO A ray oflight from a light source fig. b is reflected by a mirror through 90’ It then passes through a transparent glass plate (on which flat parts may be placed ). A shadow image of the outline or counter of the workspaces passes through the objective of the optical head and is projected by a system of three prisms to a ground glass screen. Observations are made through an eyepiece. Measurements are made by means of cross lines engraved on the ground glass screen. The screen can be rotated through 360’; the angle of rotation is read through an auxiliary eyepiece. WORKING PRINCIPLE Prof. Afaqahmed (c) Copyright
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- 36. www.company.com Company LOGO • The ideaof using profile projector, which is created by James Hartness and Russell W. Porter, came from mixing optics and measurement in a device. • The use of the term comparator for metrological equipment, had existed in other forms prior to Hartness's work; but they had remained in realms of pure science (such as telescopy and microscopy) and highly specialized applied science (such as comparing master measuring standards). Prof. Afaqahmed (c) Copyright
- 37. www.company.com (i) A singlesetting of the specimen provides observation, comparison and inspection of several dimensions and form characteristics in a projector. (ii) Several people can observe the projected image simultaneously. Thus, projectors are handy tools when images are to be inspected by a group of people. (iii) The image can be magnified according to requirement. Thus, dimensions to be inspected individually or their interrelation with other dimensions of the same part can be observed without any additional instruments. (iv) Projector provides direct measurements of various lengths and angles. Lengths are measured by graduated rulers and angles by drafting protractors. (v) Precise comparison is possible in projectors. Standard comparator charts, specially for repetitive forms such as circular arcs with different radii, angles, thread forms, gear contours can be used on optical projector screen. Such standard charts are made of glass plates. (vi) There is no physical contact between the specimen and the measuring instruments in projectors. Thus, specimen to be inspected is free from mechanical distortion or defects. This increases the accuracy in measurement. (vii) Unlike the mechanical gauges, which undergo wear and tear due to prolong uses, measurements by optical projectors are free from wear. (viii) Optically obstructed surface elements can be traced by means of projectors. PROS Prof. Afaqahmed (c) Copyright
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- 39. www.company.com Coordinate Measuring Machine (Schematic) Prof.Afaqahmed (c) Copyright
- 40. www.company.com A coordinate measuringmachine (CMM) is a device for measuring the physical geometrical characteristics of an object. This machine may be manually controlled by an operator or it may be computer controlled. Measurements are defined by a probe attached to the third moving axis of this machine. Probes may be mechanical, optical, laser, or white light, amongst others. A machine which takes readings in six degrees of freedom and displays these readings in mathematical form is known as a CMM. Definition : Prof. Afaqahmed (c) Copyright
- 41. www.company.com INTRODUCTION • Ogden developedan inspection machine in 1956,which is considered to be the first coordinate measuring machine (CMM). • A Coordinating measuring machine is an electromechanical system design to perform coordinate metrology. • CMMs are also considered as transducers that can convert physical measurements into electrical signals. • They are versatile in their capability to record measurement of complex profiles with high sensitivity (0.0025 mm) and speed. Prof. Afaqahmed (c) Copyright
- 42. www.company.com COMPONENTS OF CMM Toaccomplish measurements in 3-D, a basic CMM is composed of the following components: • Probe head and probe to contact the workpart surfaces • Mechanical structure that provides motion of the probe in three Cartesian axes and displacement transducers to measure the coordinate values of each axis In addition, many CMMs have the following components: • Drive system and control unit to move each of the three axes • Digital computer system with application software Prof. Afaqahmed (c) Copyright
- 43. www.company.com TYPES OF CMM Asper the mechanical structure the CMM are classified into six types , which are as follows: CANTILEVER MOVING BRIDGE FIXED BRIDGE HORIZONTAL ARM GANTRY COLUMN Prof. Afaqahmed (c) Copyright
- 44. www.company.com MECHANICAL STRUCTURES OF CMM Prof.Afaqahmed (c) Copyright
- 45. www.company.com CMM WORKING • Afterplacing a workpiece on the machine table, a probe is used to measure different points on it by mapping the x, y, z coordinates. • The probe operates either manually via an operator or automatically via a control system. • These points are then uploaded to a computer interface where they can be analyzed using modeling software (e.g. CAD) and regression algorithms for further development. Prof. Afaqahmed (c) Copyright
- 46. www.company.com PROS OF CMM Dimensionalmeasurement Profile measurement Angularity or orientation Depth mapping Digitizing or imaging Shaft measurement Prof. Afaqahmed (c) Copyright
- 47. www.company.com Prof. Afaqahmed (c)Copyright