"Projects" at georgesbasement.com 
 

Upgrading the Brown & Sharpe Indexing Centers
This Brown & Sharpe set of indexing centers was intended for use on a grinding machine, as there is provision only for working between centers; the main spindle center is permanently attached.  However, the existing index plate, made integral with the worm wheel, permits only a limited number of divisions for such things as spur gears, which is the use for which I have upgraded the device.
Brown & Sharpe Indexing Center

   This view shows the back side and indexed worm gear of the centers along with both the old worm gear and plain crank and the new worm gear and its articulated crank and removeable index plate. 
 

   The original pin arm was left in place but is not needed in order to operate the indexing mechanism.
 

   The old worm is shown lying underneath.
Bottom of indexing centers   The bottom view here shows how the newly adapted indexing disk is attached with a carrier that is press fit over the end of the worm shaft's housing.
  

   I made no changes to the original casting of the indexing centers; the new parts can be removed and the old parts replaced with no repairs or adapters necessary. 
 

   The new worm was made as an Acme-threaded 6 tpi screw of the same outside diameter as the original worm, even its hourglass profile. 
 

   I ground the worm's threading tool to match a B&S Acme single-point threading tool gauge. The carrier is steadied by the 0.500 inch diameter tool steel shaft of the new worm.
Top view of Brown & Sharpe indexing centers   The worm shaft has bronze thrust bearings at each end, and the end play/backlash is adjusted by rotating the articulated crank on the 1/2-13 threaded end of the shaft and then clamping it with the 1/4-20 socket head cap screw. 
 

   Another socket head cap screw, No.5-40 size, easily clamps the articulation joint of the crank so that the pin can be reliably dropped in the chosen circle of index holes. 
 

   The aluminum sector arms are clamped by three No.6-32 size flat head socket screws and rotate on the two steel plates that the clamp screws engage. The assembly rotates on the disk carrier; friction is applied by an O-ring sandwiched between the two steel plates.
    Pin mechanism
   The pin housing is hollow; the two rollpins act to hold the pin in the disengaged position and also to keep the pin from rotating away from the guiding keyway.
Pin internals  The short spring is completely compressed when the pin is withdrawn to the position in the first image above. When the pin is engaged with a hole in the index disk, the spring is completely extended. The split collar against which the spring presses at the bottom is let into a groove cut in the pin.
  

   After this picture was taken, I bent the upper end of the spring so it could not get past the bottom rollpin.
  

   The short arm of the articulated crank has an integral boss at each end; the central hole in each boss lets the arm be carried on a 3/8 inch diameter mandrel for machining.
Maker's marks   The Brown & Sharpe maker's marks do not give a model number; this indexing center pair was not made for one of Brown & Sharpe's many milling machines.  

In the 1916 Brown & Sharpe General Line Catalog, it's the  4-3/4 inch indexing centers for the No.'s 2, 12 & 13 surface and  universal & tool grinding machines.
The worm wheel has 75 teeth. The following table gives the indexing data calculated from the ratio of {75/(No.ofTeeth)}.
I have three disks with circles of (18, 24, 28, 30, 34 & 37), (38, 39, 41, 42, 43, & 46) and (47, 49, 54, 58, 62, & 66) holes.
Underlined circles must be created; best candidates are circles of 44, 52, 56, 64, 68,76, 82, 86, 88, 92, 94, 98, and 127 (the last is for metric conversions).
The worm wheel itself has indexing circles of 24, 28, 32, 36 & 40 holes; the worm is a single start type.

Counts greater than half a circle can be reduced by moving the sector backwards by the complement of the turns ratio.
Example: for 39 teeth, go two turns less 3/39th of a turn.

No. of  Teeth
Circle
Turns
No. of  Teeth Circle Turns No .of  Teeth Circle Turns No. of  Teeth Circle Turns No. of  Teeth Circle Turns No. of  Teeth Circle Turns No. of  Teeth Circle Turns
2
18
37+9/18
16
64
4+44/64
30
18
2+9/18
44
44
1+31/44 64
64
1+11/64
86
86
75/86
116
116 75/116
3
any
25
17
34
4+14/34
31
62
2+26/62
45
18
1+12/18
65
39
1+6/39
88
88
75/88
120 24
15/24
4
24
18+16/24
18
18
4+3/18
32
64
2+22/64
46
46
1+29/46
66
66
1+9/66
90
18
15/18
124
124 75/124
5
any
15
19
38
3+18/19
33
66
2+18/66
47
47
1+28/47
68
68
1+7/68
92
92
75/92
127
127 75/127
6
18
12+9/18
20
24
3+18/24
34
34
2+7/34
48
64
1+9/16
70
28
1+2/28
94
94
75/94
128
128 75/128
7
49
10+35/49
21
42
3+24/42
35
49
2+7/49
49
49
1+26/49
72
24
1+1/24
95
38
30/38
130
52 30/52
8
24
9+9/24
22
44
3+18/44
36
24
2+2/24
50
18
1+9/18
74
74
1+1/74
96
64
50/64
132
132 75/132
9
18
8+6/18
23
46
3+12/46
37
37
2+1/37
52
52
1+23/52
75
any
1
98
98 75/98 135
54
30/54
10
18
7+9/18
24
24
3+3/24
38
38
1+37/38
54
54
1+21/54
76
76
75/76
100
24
18/24
136
136 75/136
11
66
6+54/66
25
any
3
39
39
1+36/39
55
66
1+24/66
78
52
50/52
102
34
25/34
140
28
15/28
12
24
6+6/24
26
52
2+46/52
40
24
1+21/24
56
56
1+19/56
80
64
60/64
104
104 75/104 144
144 75/155
13
39
5+30/39
27
54
2+42/54
41
41
1+34/41
58
58
1+17/58
82
82
75/82
108 108 75/108 145
58
30/58
14
28
5+10/28
28
28
2+9/28
42
42
1+33/42
60
24
1+6/24
84
28
25/28
110
66
45/66
148 148 75/148
15
any
5
29
58
2+14/58
43
43
1-32/43
62
62
1+13/62
85
34
30/34
115
46 30/46 150
18
9/18
Ready to Run
Finished sector & crank pin
Indexing gear side view