03-07-2013, 01:06 PM
Angular Measurements
Angular Measurements.ppt (Size: 889 KB / Downloads: 50)
Angle is defined as the opening between two lines which meet at a point.
If a circle is divided into 360 parts, then each part is called a degree (o). Each degree is subdivided into 60 parts called minutes(’), and each minute is further subdivided into 60 parts called seconds(”).
The unit ‘Radian’ is defined as the angle subtended by an arc of a circle of length equal to the radius.
If arc AB = radius OA, then the angle q = 1 radian.
VERNIER BEVEL PROTRACTOR
It is a simplest instrument for measuring the angle between two faces of a component.
It consists of a base plate attached to a main body and an adjustable blade which is attached to a circular plate containing vernier scale.
The adjustable blade is capable of sliding freely along the groove provided on it and can be clamped at any convenient length.
The adjustable blade along with the circular plate containing the vernier can rotate freely about the center of the main scale engraved on the body of the instrument and can be locked in any position with the help of a clamping knob.
An acute angle attachment is also provided.
Limitations of Sine bars
The accuracy of sine bars is limited by measurement of center distance between the two precision rollers & hence it can not be used as a primary standard for angle measurements.
Sine principle is fairly reliable at angles less than 15o, but becomes inaccurate as the angle increases. For angles exceeding 45o, sine bars are not suitable for the following reasons:
The sine bar is physically clumsy to hold in position.
The body of the sine bar obstructs the gauge block stack, even if relieved.
Sine centre
Sine centers are used for mounting conical work pieces which can not be held on a conventional sine bar.
Sine centre consists of a self contained sine bar hinged at one roller and mounted on its own datum surface & the top surface of the bar is provided with clamps & centers to hold the work.
For the dial gauge to read zero, the accurate semi cone angle a=q=sin-1(H/L).
Numericals on building of angles
The required angle may built by wringing suitable combination of angle gauges similar to that of slip gauges.
Each angle is a wedge and thus two gauges with narrow ends together provide an angle which is equal to the sum of angles of individual gauges.
Two gauges when wrung together with opposing narrow ends give subtraction of the two angles.
Clinometer
The Clinometer is first placed on one face of the workpiece and the rotary member is adjusted till the bubble is exactly at the center of the spirit level. The angle is noted on the scale.
A second reading is taken in a similar manner on the second face of the workpiece. The included angle is then the difference between the two readings. i.e. from fig, g=180-(a+b).
Clinometers are used for checking face & relief angles on large cutting tools & milling cutter inserts.
Also used for setting jig boring machine tables & angular work on grinding machines.