gear and screw measurement
DESCRIPTION
Screw Thread measurement: Two wireScrew Thread measurement: Three wireScrew Thread measurement: Floating CarriageGear measurement: Gear tooth comparatorGear measurement: Master GearGear measurement: Using Rollers and Parkinson Gear TesterSpecial measuring Equipments: Principles of measurement using Tool Maker’s microscope,Special measuring Equipments: Principles of measurement using Profile ProjectorSpecial measuring Equipments: Principles of measurement using 3D CMMTRANSCRIPT
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MODULE NO – 310- 12 Marks
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PREPARED BY,
Afaqahmed M J , AIKTC
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Screw thread-definitionA screw thread is the helical ridge produced byforming a continuous helical groove of uniformsection on the external or internal surface of acylinder or a cone.A screw thread is a ridge wrapped around a cylinderor cone in the form of a helix, with the former beingcalled a straight thread and the latter called a taperedthread.The helical groove opened to internaland external surface
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Types of thread1. External thread: A thread formed on
outside of a work piece is known asexternal thread. Example: on bolts orstuds etc.
2. Internal thread: A thread formed on insideof a work piece is known as internalthread. Example: on a nut or female screwgauge.
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Screw Thread terminology1. Pitch: The distance from a point on a screw
thread to a corresponding point on the next threadmeasured parallel to the axis.
2. Lead :The distance a screw thread advances inone 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 cutby a plane containing the axis.
4. Major Diameter: This is the diameter of animaginary cylinder, coaxial with the screw, whichjust touches the crests of an external thread orroots o f an internal threads. It is also called as‘Nominal diameter
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5. Minor diameter: This is the diameter of animaginary cylinder, co-axial with the screw whichjust touches the roots of an external thread or thecrest of an internal thread. This is also referred to as‘root’ or ‘core diameter’.
6. Effective diameter or Pitch diameter: It is thediameter of an imaginary cylinder coaxial with theaxis of the thread and intersects the flanks of thethread such that width of the threads & width ofspaces between threads are equal.
7. Flank: It is the Thread surface that connects crestwith root.
8. Depth of thread: It is the distance between crestand root measured perpendicular to axis of screw.
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9. Angle of thread: Included angle betweensides of thread measured in axial plane.10. Helix angle: Angle that the thread makeswith plane perpendicular to thread axis.11. Flank angle: It is half the included angle ofthe thread.12. Addendum: It is the distance between thecrest and the pitch line measuredperpendicular to axis of the screw.13. Dedendum: It is the distance between thepitch line & the root measured perpendicularto axis of the screw.
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1. It consists of three main units. A base casting carries a pair ofcentres, on which the threaded work-piece is mounted. Anothercarriage is mounted on it and is exactly at 90° to it.2. On this is provided another carriage capable of moving towards thecentres. On carriage one head having a large thimble enablingreading upto 0.002 mm is provided.3. Thus the micrometer elements are exactly perpendicular to the axisof the centres as the two carriages are located perpendicular to eachother.4. On the fixed carriage the centres are supported in two bracketsfitted on either end. The distance between the two centres can beadjusted depending upon the length of tie threaded job.5. job is fitted between the centres the second carriage is adjusted incorrect position to take measurements and is located in position, Thethird carriage is then moved till the Fiducial indicator is against theset point.
Construction & Working
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6. The upper carriage is free to float on balls and enables micrometer readings to be taken on a diameter without restraint.
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Effective Diameter Measurement1. Two Wire Method
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Working
1. Place two wires / rods of identical diameter between the flanks ofthe thread
2. This method can only be carried out on diameter measuringmachine.
3. Axis of the micrometer is maintained @ 90 degree to the axis ofscrew thread.
4. Micrometer is attached with the wires which shows the readings5. Effective Diameter is calculated as
E = Effective Diameter
E = T + P
Where T = Dimension under the wires = M – 2dM = Dimension over the wiresd = Diameter of each wire
P = Value which depend on Dia & PitchP = 0.9605 p – 1.1657 d (Whitworth Thread)P = 0.866 p – d (Metric thread)
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Effective Diameter Measurement2. Three Wire Method
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Working
1. Most accurate method to measure effective diameter2. Three wires of known diameters are used : one on one side
& two on other side3. This method is precisely aligned with anvil of micrometer4. 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 ThreadM = D + 3.1657 d – 1.6 pWhere D = Outside dia2. Metric threadM = D + 3d – 1.5155 p
4. By finding the value of M we can find out E by knowing d.
Slide 18
a1 aafaq, 18-02-2016
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What is a gear ?
A gear is a wheel with teeth that mesh together with other gears.
Gears change the :
• Speed
• Torque (rot. force)
• Direction of rotating axles.
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Purpose :
To transmit rotary 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.
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TYPES OF GEARS1.According to the position of axes of the shafts. a. Parallel
1.Spur Gear2.Helical Gear3.Rack and Pinion
b. IntersectingBevel Gear
c. Non-intersecting and Non-parallelworm and worm gears
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This machine, developed by James Parkinson, is popularlyused for testing of spur gears, in pair.
The principle of this device is to mount a standard gear on afixed vertical spindle and the gear to be tested on anothersimilar spindle mounted on a similar spindle mounted on asliding carriage, maintaining the gears in mesh by springpressure.
Movements of the sliding carriage as the gears are rotatedand indicated by a dial indicator, and these variations are ameasure of any irregularities in the gear under test ,alternatively a recorder can be fitted ,in the form of a waxedcircular chart and records made of the gear variation inaccuracy of mesh.
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When the waxed paper recorder is fitted, the chart makes arevolution for each one of the gears mounted on the slidingcarriage. As the chart moves and rotates, the line tracedrecords the movements of floating carriage. A circle is drawnat the same time as the record as shown in figure.
METHOD OF MEASUREMENT
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A ray of light from a light source fig. is reflected by amirror through 90’ It then passes through atransparent glass plate (on which flat parts may beplaced ).
A shadow image of the outline or counter of theworkspaces passes through the objective of the opticalhead and is projected by a system of three prisms to aground glass screen.
Observations are made through an eyepiece.Measurements are made by means of cross linesengraved on the ground glass screen.
The screen can be rotated through 360’; the angle ofrotation is read through an auxiliary eyepiece.
WORKING PRINCIPLE
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• The idea of using profile projector, which is created by James Hartness andRussell W. Porter, came from mixing optics and measurement in a device.
• The use of the term comparator for metrological equipment, had existed inother forms prior to Hartness's work; but they had remained in realms ofpure science (such as telescopy and microscopy) and highly specializedapplied science (such as comparing master measuring standards).
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(i) A single setting of the specimen provides observation, comparison andinspection 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 ofpeople.(iii) The image can be magnified according to requirement. Thus, dimensions tobe inspected individually or their interrelation with other dimensions of thesame 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. Suchstandard charts are made of glass plates.(vi) There is no physical contact between the specimen and the measuringinstruments in projectors. Thus, specimen to be inspected is free frommechanical distortion or defects. This increases the accuracy in measurement.(vii) Unlike the mechanical gauges, which undergo wear and tear due to prolonguses, measurements by optical projectors are free from wear.(viii) Optically obstructed surface elements can be traced by means ofprojectors.
PROS
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A coordinate measuring machine (CMM) is a devicefor measuring the physical geometricalcharacteristics of an object. This machine may bemanually controlled by an operator or it may becomputer controlled. Measurements are defined bya probe attached to the third moving axis of thismachine. Probes may be mechanical, optical, laser,or white light, amongst others. A machine whichtakes readings in six degrees of freedom anddisplays these readings in mathematical form isknown as a CMM.
Definition :
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INTRODUCTION
• Ogden developed an inspection machine in1956,which is considered to be the first coordinatemeasuring machine (CMM).
• A Coordinating measuring machine is anelectromechanical system design to performcoordinate metrology.
• CMMs are also considered as transducers that canconvert physical measurements into electricalsignals.
• They are versatile in their capability to recordmeasurement of complex profiles with highsensitivity (0.0025 mm) and speed.
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COMPONENTS OF CMM
To accomplish measurements in 3-D, a basic CMM iscomposed 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 tomeasure the coordinate values of each axis
In addition, many CMMs have the following components:
• Drive system and control unit to move each of the threeaxes
• Digital computer system with application software
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TYPES OF CMM
As per the mechanical structure the CMM are classified into six types , which are as follows:
CANTILEVER MOVING BRIDGE FIXED BRIDGE HORIZONTAL ARM GANTRY COLUMN
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CMM WORKING
• After placing a workpiece on themachine table, a probe is used tomeasure different points on it bymapping the x, y, z coordinates.
• The probe operates either manuallyvia an operator or automatically viaa control system.
• These points are then uploaded to acomputer interface where they canbe analyzed using modelingsoftware (e.g. CAD) and regressionalgorithms for further development.
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PROS OF CMM
Dimensional measurement Profile measurement Angularity or orientation Depth mapping Digitizing or imaging Shaft measurement
