A gear with a conical indexing surface is called a bevel gear. According to the shape of the tooth line, bevel gears can be divided into straight teeth, helical teeth and curved teeth. Bevel gears are used for cross shaft gear transmission and cross shaft gear transmission. For the processing of milling straight bevel gears, let's introduce it in detail below.
Geometric characteristics of spur bevel gears
1. The top conical surface (top cone), indexing conical surface (sub cone) and root conical surface (root cone) of straight bevel gear intersect at one point.
2. The teeth of spur bevel gears are distributed on the conical surface, and the grooves are wide and deep at the big end and narrow and shallow at the small end. The teeth gradually shrink from the big end to the top of the cone.
3. In the developed surface of the back cone of a spur bevel gear (usually the big end face of the bevel gear tooth, and the prime line of the back cone is perpendicular to the sub cone), the tooth profile curve of the tooth is an involute.
4. The module of straight bevel gear is different from big end to small end. In the design and calculation of bevel gear, it is stipulated to take the big end module as the basis and adopt the standard module.
Straight bevel gear milling cutter and its selection
The teeth of straight bevel gear are distributed on the conical surface, and the tooth shape gradually shrinks from the big end to the top of the cone. The diameters of the big end and the small end of the bevel gear are not equal, and the diameters of the base circle are not equal. The base circle diameter of the big end is large, and the curvature of its involute tooth profile curve is small (that is, the tooth profile curve is relatively straight); The diameter of the base circle at the small end is small, and the curvature of the involute tooth profile curve is larger (that is, the tooth profile curve is more curved). The tooth profile of straight bevel gear milling cutter can only be designed according to a certain section of the prime line of the indexing conical surface, and the tooth profile of the processed gear can only be more accurate in a certain section, while there are certain errors in other sections. Therefore, the precision of straight bevel gear formed by bevel gear milling cutter is low. The less the number of teeth or the larger the width of bevel gear, the greater the error.
Usually, the tooth profile curve of the straight bevel gear milling cutter is designed according to the tooth profile curve of the big end, and the thickness of the milling cutter is designed according to the slot width of the small end, so as to ensure that the blade can pass through the small end in the milling process. Therefore, the straight bevel gear milling cutter is thinner than the straight cylindrical gear milling cutter with the same modulus.
Milling of straight bevel gear
Straight bevel gears can be machined on horizontal or vertical milling machines with disk bevel gear cutters. When machining on a horizontal milling machine, it can be divided into longitudinal (horizontal) feed milling method and vertical feed milling method according to the feed direction. When using the longitudinal feed milling method, first adjust the spindle of the dividing head to be parallel to the worktable and the rotation plane of the milling cutter, and check the radial circular runout of the big end and the small end after the gear blank is installed. Then make the main shaft of the dividing head tilt up by an angle, which should be equal to the root cone angle of the processed bevel gear.
When the root cone angle of the bevel gear is large, and the length and diameter are also large, it is possible that even if the workbench is at the lowest position (the lifting table will touch the base), the tooth groove bottom of the bevel gear cannot pass under the milling cutter. At this time, the vertical feed milling method can be used for processing.