Manufacturing Manufacturing Processes-1 Lecture#6
Date: 18-10-2012
INDEXING Definition: Indexing is an operation of dividing a periphery of a cylindrical workpiece into equal number of divisions by the help of index crank and index plate when milling gear teeth, squares, hexagons, and octagons. Also used to rotate workpiece at predetermined ratio to table feed rate
A manual indexing head includes a hand crank. Rotating the hand crank in turn rotates the spindle and therefore the work piece. The hand crank uses a worm gear drive to provide precise control of the rotation of the work. The work may be rotated and then locked into place before the cutter is applied, or it may be rotated during cutting depending on the type of machining being done. Most dividing heads operate at a 40:1 ratio; that is 40 turns of the hand crank generates 1 revolution of the spindle or work piece. In other words, 1 turn of the hand crank rotates the spindle by 9 degrees. Because the operator of the machine may want to rotate the part to an arbitrary angle indexing plates are used to ensure the part is accurately positioned
. Types of Indexing: 1. 2. 3. 4. 5.
Direct Indexing Simple Indexing Compound Indexing Differential Indexing Angular Indexing
Direct indexing:
In direct indexing,the index plate is directly mounted on the dividing head spindle with a standard indexing plate having 24 holes all factors of 24 can be indexed i.e the work can be divided into 2,3,4,6,8,12, and 24 parts 1 10-ME-33,54,57
Manufacturing Processes-1 Lecture#6
Date: 18-10-2012
Simplest form of indexing
Performed by disengaging worm shaft from worm wheel by means of eccentric device in dividing head, spring-loaded tongue lock engages numbered slots in index plate
Used for quick indexing of workpiece when cutting flutes, hexagons, squares, etc.
Simple indexing:
In simple or plain indexing,an indexed plate is fitted on the worm shaft and locked through a locking pin. A typical set has following number of holes. Plate 1:
15,16,17,18,19,20
Plate 2:
21,23,27,29,31,33
Plate 3:
37,39,41,43,47,49
Compound indexing:
When none of the indexed plate has a hole circle which would enable the work to be divided by simple indexing method we can use compound indexing . The procedure is explained below; Let; z = no. of division needed Crank rotations for each indexing= 40/z i. ii. iii. iv.
Write z above and 40 below a straight line and factorized them Select 2 numbers representing 2 hole circles in the same plate. Write these numbers below 40 and factorized them. Write their difference above z and factorize it. These hole numbers are too be chosen in such a manner that all the factors above the line get cancelled out. Let these holes numbers be N1 and N2 Let n1 be the numbers of holes indexed in N1 hole circle and n2 the number of holes to be indexed in N2 hole circle. Then; n 1/N1 +/- n 2 /N2 = 40/z 2
10-ME-33,54,57
Manufacturing Processes-1 Lecture#6
Date: 18-10-2012
n1 and n2 are found by hit and trail method. Example
Let z=77 Steps ;
i. ii.
77=11x7 40=2 x 2 x 2 x 5 Let N1= 21 and N2 = 33 Difference 12= 2 x 2 x 3 Therefore 77 = 11 x 7 40 = 2 x 2 x 2 x 5 21 = 7 x 3 33 = 11 x 3 Since all the factors above the line get cancelled out, therefore, selection of N1 and N2 is correct.
Now; n1 /21 +/- n 2/33 = 40/77 Values of n1 and n2 would be determined by hit and trail method. Differential indexing:
Differential indexing in reality is an automatic method of doing compound indexing and is achieved in a single step.
Used when 40/N cannot be reduced to a factor of one of the available hole circles.
Index plate must be revolved either forward or backward part of a turn while index crank turned to attain proper spacing (indexing).
Procedure:
Let z = no. of divisions required to be indexed k = number very nearly equals to z 3 10-ME-33,54,57
Manufacturing Processes-1 Lecture#6
Date: 18-10-2012
No. of crank turns for each simple indexing n = 40/k
No. of crank turns needed for z indexing N = 40z/k
i. ii.
If N >40, then(N-40) turns have to be subtracted if N < 40 , then (40-N) turns indexed plate should rotate in same direction as of crank.
The gear ratio will be: I=40(k-z)/k Example :
Do differential indexing for 93 divisions Solution;
z = 93, therefore, Let k = 90, which can be simple indexed each indexing = 40/90 =4/9 =8/18, i.e., 8 holes in an 18 holes circle. For 93 indexing’s, N = 8/18 x 93 = 41 1/3 Since N>40, the indexed plate must rotate 4/3 backward I=40(k-z)/k= 40/90 x 3 =4/3 In brown and sharp dividing head, the gears supplied are 24,28,32,40,44,48,56,64,72,86,100 Angular Indexing:
Angular indexing is used when it is necessary to cut grooves subtending a given angle at the center of the circle. Now 1 turn of crank = 9◦ of the spindle. Example: Calculate indexing for 60º Indexing
60
9
6
2 3
6 full turns plus 12 holes on 18 hole circle
4 10-ME-33,54,57
Manufacturing Processes-1 Lecture#6
Date: 18-10-2012
Example: Calculate indexing for 24º30'
First, convert angle into minutes (24 x 60') = 1440' now add 30' = 1470‘ Convert 9° to minutes 9°x90’ = 540’ Divide
1470'/540' = 2 13/18
2 full turns and 13 holes on 18 hole circle
Therefore ; Turns of crank to give any angle = angle required/9. Example: Do angular indexing for 51◦37’ Solution: Indexing = 51◦ 37’/9 =5 + 397’/540’ Let us convert the residual turn to a continued fraction, 397 ) 540 ( 1 397 143 ) 397 (2 286 111 ) 143 ( 1 111 32 ) 111 ( 3 96 15 ) 32 ( 2 30 2 ) 15 ( 7 14 5 10-ME-33,54,57
Manufacturing Processes-1 Lecture#6
Date: 18-10-2012
1)2(2 2/0 So we have, 1,2/3,3/4,11/15,25/34,186/253,397/540 Now select Those values of numerator and denominator which occur in 1,2,3 plates. So, 5 x 11/15 x 9 = 51° 36’ Difference of one minute occurs. (not acceptable) So now we have Cinnaciti and Parkinson 1- 24,25,28,30,34,37,38,39,41,42,43 2- 46,47,49,51,53,54,57,58,59,62,66
So
5 x 25/34 x 9 = 51°37’ 3 11/16’’
Now it I acceptable because it has minimum difference of seconds.
6 10-ME-33,54,57
