# The computer drawing method of standard spur gear profile

In gear processing, we often use the tooth profile template when checking the tooth profile. In the past, in this case, the technician needs to draw the tooth profile template point by point according to the manual, which is very troublesome. Every gear with different module needs to be redrawn, and the workload can be imagined. Now the computer is widely used. According to the formation principle of the involute and the cutting principle of the gear, and combined with the practical experience, we have developed a method of drawing the tooth profile by using the computer. We can draw the tooth profile of the gear with different number of teeth (the module is 1) as the model. For different modules, as long as we enlarge the corresponding multiple, we can draw the corresponding tooth profile. In this way, we can draw the tooth profile The tooth profile drawing is not only more accurate than that drawn by hand, but also can be done once and for all, which is much more convenient.

##### A detailed drawing of the profile of spur gear

Next, we take the gear with 18 teeth as an example to introduce the drawing method of this kind of tooth profile in detail. We divide the drawing of tooth profile into the drawing of involute tooth profile and the drawing of base circle and root circle according to the different components of tooth profileIf the number of gear teeth is 18 and the modulus is 1, then the radius of graduation circle is 8.457mm. First draw the base circle, then take an arc with an angle of 3 on the base circle, and the measured value is 0.44mm

Draw a vertical line of horizontal axis with a length of 0.44mm tangent to the base circle, and then circle the center of the base circle to array the line and its vertical horizontal line, with an angle of 3 degrees

Extend the tangent line of the base circle obtained by the array: the tangent line at 3 ° remains unchanged, the tangent line at 6 ° doubles, the tangent line at 9 ° doubles, and the tangent line at 12 ° doubles By analogy, the tangent line at 45 ° is extended 15 times. A smooth curve connecting the end points of each tangent extension line in turn

Draw the graduation circle (radius: 9mm) and tooth top circle (radius: 10 mm) of the gear, connect the intersection of the over degree circle and the involute with the center of the circle, rotate the line to the horizontal (the curve obtained in the third step rotates with it), clear other auxiliary lines, then draw a ray with an angle of 5 degrees through the center of the circle, which is the symmetry line of one tooth of the gear, turn the curve to the mirror phase, and the tooth top circle and the base circle The curve part is the involute part of a gear tooth

The involute part array of a gear tooth is obtained, and the involute tooth profile of a gear with a module of 1 and a number of teeth of 18 is obtained.

The above five steps are the drawing of involute part of gear teeth. From the sixth step, draw the tooth profile of base circle and root circle.First draw the rack figure with module 1, which is 0.25mm higher than the standard rack top

In the actual processing of the gear, the rack moves 0.157mm horizontally every 1 ° of gear rotation. According to this principle, take a tooth of rack to study, move it horizontally to the left by 0.157mm, rotate it around the center of the gear by 1 °, then move it horizontally to the left by 0.157mmx2, and rotate it around the center of the gear by 2 ° , and so on, when it is moved horizontally to the left by 0.157mmx7, it should be rotated around the center of the gear by 7 °

Take an envelope line from the point tangent to the track of each rack tooth in turn to the base circle, take the fillet of the rack tooth top at the tooth root, and get the tooth profile of the base circle and the tooth root circle section of the rack, then get a complete tooth profile along the mirror phase of the symmetrical line at the involute tooth profile of the rack, and finally get all the tooth profiles of the rack along the center array, so far, the tooth profile of the rack is all drawn Complete.

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