Experiment No: 9Date: ___/___/2013

Experiment No: 08 Date:___/___/2015

Title: To measure the external taper of a taper shank drill using standard rollers and comparing the results with plate protractor measurements.Objectives:

Students will be able to knowi. What Taper shank drill is.ii. Different ways of measuring external taper.iii. Measurement of taper shank drill using standard rollers.

Theory:

Theshankis the end of adrill bitgrasped by thechuckof adrill. The cutting edges of the drill bit contact the workpiece and are connected via the shaft with the shank, which fits into the chuck. In many cases a general-purpose arrangement is used, such as a bit with cylindrical shaft and shank in a three-jaw chuck which grips a cylindrical shank tightly. Different shank and chuck combination can deliver improved performance, such as allowing higher torque, greater centering accuracy, or moving the bit, but not the chuck, with a hammer action.Different kinds of shanks are available in marked based on their geometry including brace shank (a), straight shank (b), hex shank (c), triangular shank (d) and taper shank.(a)(b)(c)(d)

Fig.1 Types of Shank drill bits

Taper Shank Drill:A taper may be defined as a uniform change in diameter of a workpiece measured along its axis. Tapers in the inch system are expressed in taper per foot, taper per inch or degrees. Fig.2 Taper shank Drill

External taper measurement:[1] Plate Protactor: Protractor is the simplest device used to measure the angles of workpieces and cutting tools. It is graded from 0 to 180 degrees, provided with measuring arm which rotates relative to protractor pivot. Pointer; at the end arm, is used to specify the protractor reading. Plate protractor is used for measurement of angles of workpieces, external angles, slopes, drill angles, marking etc.

[2] Combination Squares: These are used for marking angles, squares and level.

[3] Universal Bevel Protector: Universal Bevel Protractor is the most accurate device for angle measurement of workpieces and cutting tools in workshops and labs. Its accuracy reaches 1/12 (= 5).

[4] Sine bar: The sine bar is provided with locating angular grooves in which two rollers of equal diameter are placed. The taper is mounted between the two centers on the table. He sine table is placed on a surface plate and adjusted by means of slip gauges until the top surface of taper shaft is made parallel to the surface plate. This can be chaecked by a dial gauge mounted on the surface plate.

[5] Standard rollers:The tapered element is to be placed with its small end on a surface plate as shown in figure. Two precise rollers of equal diameter are then placed on the surface plate to contact the surface of the taper plug of two points diametrically opposite.

Measurement of taper shank drill using Standard rollers:Fig.3

If the tapered element has a taper length not exceeding 100mm, then standard rollers alongwith slip gauges and micrometer. Tapered shaft is placed on surface plate and two precision rollers of equal diameters are then placed on surface plate to contact the surface of the taper plug of two points diametrically opposite. The distance L1 across the rollers can be measured by the micrometer. The same rollers are placed on two equal columns of slip gauges of height h and the dimension L2 across them is also measured.Then, L2 L1 = 2h. tan Tan = L2 L1/2hWhere, = taper angle or half the included cone angle.

Observations and calculations: Diameter of Precision balls used = Distance across the rollers at base, L1= Height of slip gauges, h =Distance across the rollers at height h, L2=Since, Tan = L2 L1/2hTherefore, standard rollers =

Now, measure taper angle using plate protractor plate protractor = Percentage Error =

Comments:

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