unit 3 Form Measurement

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Metrology and Measurement

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Form Measurement:

Form Measurement Unit 3

Syllabus :

Syllabus Measurement of screw threads-Thread gauges, floating carriage micrometer-measurement of gears-tooth thickness-constant chord and base tangent method-Gleason gear testing machine - radius measurements-surface finish, straightness, flatness and roundness measurements

PowerPoint Presentation:

Screw thread measurement Gear measurement Radius measurement Surface Finish measurement Straightness measurement Flatness and roundness measurements.

Screw thread:

Screw thread

Terminology :

Terminology Crest It is top surface joining the two sides of thread. Flank Surface between crest and root. Root The bottom of the groove between the two flanks of the thread

Contd.,:

Contd., Pitch The distance measured parallel to the axis from a point on a thread to the corresponding next point. Helix angle: The helix is the angle made by the helix of the thread at the pitch line with the axis. Flank angle Angle made by the flank of a thread with the perpendicular to the thread axis

Contd.,:

Contd., Depth of thread The distance between the crest and root of the thread Major diameter: Diameter of an imaginary co-axial cylinder which would touch the crests of external or internal thread. Minor diameter (Root diameter or Core diameter): Diameter of an imaginary co-axial cylinder which would touch the roots of an external thread.

Contd.,:

Contd., Addendum Radial distance between the major and pitch cylinders For external thread. Radial distance between the minor and pitch cylinder For internal thread. Dedendum Radial distance between the pitch and minor cylinder = For external thread. Radial distance between the major and pitch cylinders = For internal thread

Errors in Screw Thread :

Errors in Screw Thread Major diameter error reduction in the flank contact interference with the matching threads Minor diameter error Interference reduction of flank contact

Contd.,:

Contd., Effective diameter error Pitch error the total length of thread engaged will be either too high or too small Flank angles error Crest and root error

Pitch Errors Classification:

Pitch Errors Classification Progressive error Periodic error Drunken error Irregular error

Errors in Thread:

Errors in Thread 1) Progressive error: The pitch of the thread is uniform but is longer or shorter its nominal value and this is called progressive error .

Contd.,:

Contd., 2. Periodic error These error repeats itself at regular intervals along the thread. Causes of periodic error: Teeth error in gears. Lead screw error. Eccentric mounting of the gears.

Contd.,:

Contd.,

Contd.,:

Contd., 3) Drunken error: Drunken errors are repeated once per turn of the thread in a Drunken thread. In Drunken thread the pitch measured parallel to the thread axis. If the thread is not cut to the true helix the drunken thread error will form

Contd.,:

Contd., 4) Irregular errors: It is vary irregular manner along the length of the thread. Irregular error causes: 1. Machine fault. 2. Non-uniformity in the material. 3. Cutting action is not correct. 4. Machining disturbances

MEASUREMENT OF VARIOUS ELEMENTS OF THREAD:

MEASUREMENT OF VARIOUS ELEMENTS OF THREAD 1) Major diameter 2) Minor diameter 3) Effective or Pitch diameter 4) Pitch 5) Thread angle and form angle

Major Diameter:

Major Diameter Ordinary micrometer Bench micrometer

Measurement by Bench micrometer::

Measurement by Bench micrometer:

Measurement by Bench micrometer::

Measurement by Bench micrometer: Then the cylinder is replaced by the threaded work piece and the new reading is taken

Measurement by Bench micrometer::

Measurement by Bench micrometer:

Measurement by Bench micrometer::

Measurement by Bench micrometer:

Measurement of the major diameter of an Internal thread::

Measurement of the major diameter of an Internal thread : The major diameter is usually measured by thread comparator fitted with ball-ended styli. First the Instrument is set for a cylindrical reference having the same diameter of major diameter of internal thread and the reading is taken. Then the floating head is retracted to engage the tips of the styli at the root of spring under pressure. For that the new reading is taken,

Measurement of the major diameter of an Internal thread::

Measurement of the major diameter of an Internal thread:

Measurement of Minor diameter:

Measurement of Minor diameter The minor diameter is measured by a comparative method by using floating carriage diameter measuring machine and small ‘ V pieces which make contact with the root of the thread. These V pieces are made in several sizes, having suitable radii at the edges. V pieces are made of hardened steel. The floating carriage diameter-measuring machine is a bench micrometer mounted on a carriage.

Measurement of Minor diameter:

Measurement of Minor diameter

Measurement of Minor diameter:

The threaded work piece is mounted between the centers of the instrument and the.V pieces are placed on each side of the work piece and then the reading is noted. After taking this reading the work piece is then replaced by a standard reference cylindrical setting gauge. Measurement of Minor diameter

Measurement of Minor diameter of Internal threads::

Measurement of Minor diameter of Internal threads: The Minor diameter of Internal threads are measured by 1. Using taper parallels 2. Using Rollers .

Measurement of Minor diameter of Internal threads::

Measurement of Minor diameter of Internal threads: Using taper parallels: For diameters less than 200mm the use of Taper parallels and micrometer is very common. The taper parallels are pairs of wedges having reduced and parallel outer edges. The diameter across their outer edges can be changed by sliding them over each other.

Measurement of Minor diameter of Internal threads::

Measurement of Minor diameter of Internal threads: Using rollers: For more than 200mm diameter this method is used. Precision rollers are inserted inside the thread and proper slip gauge is inserted between the rollers. The minor diameter is then the length of slip gauges plus twice the diameter of roller.

Measurement of Effective Diameter:

Measurement of Effective Diameter One wire Two Wires Three wires method

One wire method:

One wire method

Two wire method:

Two wire method In this method wires of suitable size are placed between the standard and the micrometer anvils

Three Wire Method:

Three Wire Method

Pitch measurement:

Pitch measurement Pitch measuring machine Tool makers microscope Screw pitch gauge

Pitch measuring machine:

Pitch measuring machine

Tool makers microscope:

Tool makers microscope

Thread form and flank angle measurement:

Thread form and flank angle measurement Thread gauge Ring gauge Optical projectors

Gear Measurement:

Gear Measurement Types of gears Spur gear Spiral gear Helical gears Bevel gears Worm and Worm wheel Rack and Pinion:

Gear tooth Terminology :

Gear tooth Terminology

PowerPoint Presentation:

Tooth profile It is the shape of any side of gear tooth in its cross section Pitch circle It is the imaginary circle of gear that rolls without slipping over the circle of its mating gear. Addendum circle The circle coincides with the crests (or) tops of teeth. Dedendum circle (or) Root circle This circle coincides with the roots (or) bottom on teeth

PowerPoint Presentation:

Module(m) It is the ratio of pitch circle diameter to the total number of teeth Face Part of the tooth in the axial plane lying between tip circle and pitch circle. Flank Part of the tooth lying between pitch circle and root circle. Top land Top surface of a tooth

Gear Errors:

Gear Errors Profile error The maximum distance of any point on the tooth profile form to the design profile. Pitch error Difference between actual and design pitch Cyclic error Error occurs in each revolution of gear Run out: - Total range of reading of a fixed indicator with the contact points applied to a surface rotated, without axial movement, about a fixed axis

Gear Errors:

Gear Errors Eccentricity: - Half the radial run out Wobble Run out measured parallel to. the axis of rotation at a specified distance from the axis Radial run out Run out measured along a perpendicular to the axis of rotation.

Gear Errors:

Gear Errors Eccentricity: - Half the radial run out Wobble Run out measured parallel to. the axis of rotation at a specified distance from the axis Radial run out Run out measured along a perpendicular to the axis of rotation.

Gear Errors:

Gear Errors Axial run out Run out measured parallel to the axis of rotation at a speed Periodic error Error occurring at regular intervals

GEAR MEASUREMENT:

GEAR MEASUREMENT Run out Pitch Profile Back lash Tooth thickness Alignment

Run out:

Run out In the testing the gears are placed in the mandrel and the dial indicator of the tester possesses special tip depending upon the module of the gear and the tips inserted between the tooth spaces and the gears are rotated tooth by tooth and the variation is noted from the dial! indicator

Pitch measurement:

Pitch measurement Point to point measurement (i.e. One tooth point to next toot point) Direct angular measurement

Tooth to Tooth measurement:

Tooth to Tooth measurement

Direct Angular Measurement:

Direct Angular Measurement Measuring the error by using set dial gauge against a tooth in this method the position of a suitable point on a tooth is measured after the gear has been indexed by a suitable angle If the gear is not indexed through the angular pitch the reading differs from the original reading. The difference between these is the cumulative pitch error

Profile checking:

Profile checking Optical projection method Involute measuring machine

Involute measuring machine:

Involute measuring machine

Backlash:

Backlash Backlash is the distance through which a gear can be rotated to bring its nonworking flank in contact with the teeth of mating gear The determination of backlash is, first one of the two gears of the pair is locked, while other is rotated forward and backward and by the comparator the maximum displacement its measured

Tooth thickness measurement:

Tooth thickness measurement Gear tooth vernier caliper method (Chordal thickness method) Base tangent method

Gear tooth vernier caliper:

Gear tooth vernier caliper

Base tangent method:

Base tangent method

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