Screw Thread And Gear Measurement Pdf

NPTEL Mechanical Engineering - Metrology

Draw the root diameter light blue by drawing a circle about O with a radius smaller than the pitch circle by the value of the dedendum. It is the surface of the gear tooth above the pitch surface.

Pitch comparator Two dial gauges on adjacent teeth with the gear mounted in centres. This is used to measure the Chordal Thickness of the gear tooth. The enlarged image can be compared with accurate drawing made to the scale of magnification.

For a drunken thread, it will be a curve as shown in fig b. Worktable is placed on the base of the instrument.

The composite deviation of a circular part during one full rotation of Eccentricity is the distance of the axis from the geometric center. The gear is indexed through successive pitches to give a constant reading on dial A. The floating carriage diameter-measuring machine is a bench micrometer mounted on.

This is measured using Gear eccentricity testers. This is the one having erratic pitch, in which the advance of the helix is irregular in one complete rotation. For a true thread, if the thread is imagined to be unwound from the pitch cylinder, the helix will be a straight line. The eccentricity in the pitch circle is called runout. Considering one gear tooth, the theoretical values of w and d can be found out which may be verified by the instrument.

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Since the cycloidal teeth have wider flanks, therefore the cycloidal gears are stronger than the involute gears, for the same pitch. Interpretation of Hydraulic Fracturing Pressure in Low permeability. This process is known as gauge setting.

Thread and gear measurement.ppt

The diameter across their outer edges can be changed by sliding them over each other. As the chart moves and rotates, the line traced records the movements of floating carriage.

The fiducial indicator is used to ensure all the measurements are made at same pressure. The measurements are made by means of cross lines engraved on the ground glass screen.

NPTEL Mechanical Engineering - Metrology


It is the radial distance of a tooth from the pitch circle to the top of the tooth. One wire, two wire, three wire method.

Gear eccentricity testers. Screw thread- definition A screw thread is a continuous helical groove of specified cross-section produced on the external or internal surface of a cylinder or a cone. It is the circle from which gear teeth profiles are generated. If the size of the wire is such it contacts the flanks at the pitch line, it is called the best size of wire which can be determined by geometry of screw thread.


Included angle between sides of thread measured in axial plane. If the development of the thread is taken then the drunken can be visualised. The face and flank of involute teeth are generated by a single curve where as in cycloidal gears, exercices corrigs d electrostatique pdf double curves i.

Hence some backlash is necessary. It is the width of the gear tooth measured parallel to its axis. The Pressure angle indicates the angle at which the contact force between gear teeth occur. This repeats itself at regular intervals along the thread.

Though there are advantages of cycloidal gears but they are outweighed by the greater simplicity and flexibility of the involute gears. By rotating the gear, tooth by tooth, dial gauge readings over the rollers can be noted and plotted in the form of a graph.

Documents Similar To thread and gear measurement. Possible sources are faults in the machine and irregular cutting action resulting from material non uniformity. Similar to Pitter machine.


The wires may be held in hand or hung from a stand. The tooth flank is the tooth surface below the pitch circle, parallel to the axis of the gear. In involute system, the basic rack has straight teeth and the same can be cut with simple tools. The dial indicator of the tester possesses special tip depending upon the module of the gear to be checked.

Thread and gear measurement.ppt

For diameters less than mm the use of Taper parallels and micrometer is very common. The distance between the fixed and sensitive tip is equivalent to base pitch of the gear.

The main art thus lies in obtaining a perfect cast. Read the horizontal vernier slide and note the reading. The rotation of micrometer head produces movement of the longitudinal carriage along the bed of the base Another carriage carrying the indicating and amplifying units comprising stylus. Draw a circle about O which is tangent to the line of action.

Lead The distance a screw thread advances in one turn. It is the distance between terminology Depth of crest and root measured perpendicular to axis of screw. Readings are taken in this manner until the whole length of the screw thread has been covered.

It gives the chordal thickness of tooth. The properly set-up instrument is applied to the gear so that all the three tips contact the tooth profile. It is also known as pitch diameter. An indirect approach of measuring internal dia is obtained by obtaining the cast of the Thread.

Draw a tangent to the pitch circle pink. It is the circle drawn through the bottom of the teeth. The distance from a point on a screw thread to a corresponding point on the next thread measured parallel to the axis. Set the chordal depth addendum on the vertical slide of the gear tooth vernier and then insert the jaws of the instrument on the tooth to be measured. It is necessary to use suitable indexing device to obtain accurate results.