For example, use the following procedure to make

a gear 3.250 inches in diameter that has 24 teeth:

1. Find the pitch diameter (PD) by using the

formula:

2. Find the diametral pitch (DP) by using the

formula:

run from 1 to 48 diametral pitch and 8 cutters to each

3. Find the whole depth of tooth (WD) by using

pitch.

the formula:

To check the dimensional accuracy of gear teeth,

use a gear tooth vernier caliper (see fig. 14-3). The

vertical scale is adjusted to the chordal addendum (a c)

and the horizontal scale is used to find the chordal

thickness (tc). Before you calculate the chordal

addendum, you must determine the addendum (ADD)

You can select the cutter to machine the gear teeth

and circular thickness (Ct).

as soon as you compute the diametral pitch. Formed

gear cutters are made with eight different forms

To determine the addendum, use the formula:

(numbered from 1 to 8) for each diametral pitch. The

number of the cutter depends upon the number of teeth

the gear will have. The following chart shows which

cutter to use to cut various numbers of teeth on a gear.

Using the values from the preceding example,

If, for example, you need a cutter for a gear that has

24 teeth, use a No. 5 cutter since a No. 5 cutter will cut

all gears containing from 21 to 25 teeth.

To determine the circular thickness, use the

Range of teeth

Number of cutter

formula:

135 to a rack

1

55 to 134

2

35 to 54

3

Using the values from the preceding example,

26 to 34

4

21 to 25

5

The formula used to find the chordal addendum is

17 to 20

6

14 to 16

7

12 to 13

8

Most cutters are stamped to show the number of the

cutter, the diametral pitch, the range for the number of

the cutter, and the depth. Involute gear cutters usually

14-4

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