When the first column ratio and teeth numbers fall between those given in the table, the tabular values are found by interpolating as seen in the following examples:
EXAMPLES OF TABULAR VALUES AND SETTING NUMBERS.
_Take a pair of 16 and 56 teeth; radii 5.09 and 17.82 inches respectively; and 2 inches pitch._
+----------------+------+----------------+------+---------------+-------+ | |Number} | | First Column | Tab. | |Kind of Gearing.| of } Kind of Flank. |Ratio | Ratio. | Val. | | |Teeth.} |Radii.+--------+------+---+---+ | | | | | Flank. |Face. |[A]|[B]| +----------------+------+----------------+------+--------+------+---+---+ |Epicycloidal, }|Small |Radial | .29 |Radial | .29 |.. |.44| |Radial Flanks }|Large |Radial | 3.5 |Radial | 3.5 |.. |.44| |Epicycloidal, } |Small |Curved 2 deg. | .29 | 2 | .87 |.63|.36| |Curved Flanks.} |Large |Curved 3 deg. } | 3.5 | 3 | 7. |.82|.30| |Epicycloidal, }|Small |"Sets," Divide} | 2. | 2 | 2. |.63|.26| |Interchange'bl.}|Large |Radii by 2.55 } | 7. | 7 | 7. |.40|.30| |Epicycloidal, } |Pinion|Curved 2 deg. | | 2 |Pinion|.63|.44| |Internal. } |Wheel |Int. face 7 deg.| 3.5 |Pinion | 7[8] |.84|.39| |Epicycloidal, }|Pinion|Curved 2 deg. | | 2 |Pinion|.63|.44| |Rack & Pinion. }|Rack |Parallel | |Parallel|Rack |.. |.31| |Involute } |Small |Face and Flank | | Pinion. | .44 | |Gearing. } |Large |One Curve | | Pinion. | .84 | +----------------+------+----------------+------+--------+------+-------+
[8] The face being here internal, the tabular value is to be found under "flanks." If bevels, use ratio radii .082 and 12.25; and teeth numbers 16.6 and 203.8 respectively.
WALKER'S PATENT WHEEL SCALE.--This scale is used in many manufactories in the United States to mark off the teeth for patterns, wherefrom to mould cast gears, and consists of a diagram from which the compasses may be set to the required radius to strike the curves of the teeth.
The general form of this diagram is shown in Fig. 139. From the portion A the length of the teeth, according to the pitch, is obtained. From the portion B half the thickness of the tooth at the pitch line is obtained. From the part C half the thickness at the root is obtained, and from the part D half the thickness at the point is obtained.