Omni Gear and Machine Corporation - Toll Free: (800) 876-7216 - Fax: (815) 723-9207

Span
Measurements

  

SPAN MEASUREMENTS
30º PA
N T

W
6
7
8
9		 2
2
2
2		 4.3604
4.4069
4.4534
4.5000
10
11
12
13		 2
3
3
3		 4.5465
7.3138
7.3604
7.4069
14
15
16
17		 3
3
3
4		 7.4534
7.5000
7.5465
10.3138
18
19
20
21		 4
4
4
4		 10.3604
10.4069
10.4534
10.5000
22
23
24
25		 4
5
5
5		 10.5464
13.3168
13.3604
13.4069
26
27
28		 5
5
5		 13.4534
13.5000
13.5464
N T

W
29
30
31
32		 6
6
6
6		 16.3138
16.3604
16.4069
16.4534
33
34
35
36		 6
6
7
7		 16.5000
16.5465
19.3138
19.3604
37
38
39
40		 7
7
7
7		 19.4069
19.4534
19.5000
19.5465
41
42
43
44		 8
8
8
8		 22.3138
22.3604
22.4069
22.4534
45
46
47
48		 8
9
9
9		 22.5000
25.2671
25.3138
25.3604
49
50
 		 9
9
 		 25.4069
25.4534
 
The limitations of span measurement are:
1) Span measurement cannot be applied when a combination of helix angle and narrow face width prevent the caliper from spanning a sufficient number of teeth.
2) Readings are influenced by errors in base pitch, tooth profile, and lead.  Readings would be erroneous if attempted on a portion of profile, which had been modified from true involute shape.

Inspection of Tooth Thickness by Means of a Span Measurement.