The gear hob (1) The gear hob The gear hob is a tool that cuts gears using the generative method according to the principle of helical gear pair meshing. The gear hob is equivalent to a pinion, and the cut gear is equivalent to a large gear. The gear hob is a helical gear with a large helix angle β0 and a small number of threads (1 to 3 teeth), a long tooth, and a helical gear that can index a large number of cylinders around a hob, which is like a helix angle γz. A small worm. To form the cutting edge, several flutes are milled along the axis at the end of the worm to form the front and front corners; the flank and relief angles are formed by the scraper and spatula, as shown in Fig. 9-25.
(b) Basic worm gear hob blades on both sides of the gear hob are the intersection of the front and side scoop surfaces. It should be distributed on the spiral surface of the worm. This worm is called the basic worm of the hob.
There are three basic worms:
1. Involute worm Involute worm thread side flanks are involute helicoids. The intersection between the arbitrary plane tangent to the base cylinder and the involute helix plane is a straight line. The end profile is involute. The line of intersection between the axial profile of the involute worm and the involute helicoid is a curve. The hob made with this basic screw has no tooth design error and the precision of the cut gear is high. However, it is difficult to make a hob.
2. Archimedes worm archimedes worm screw side is the Archimedes spiral surface. The line of intersection between the worm axis profile and the Archimedes spiral helix surface is a straight line, and the other profiles are curves. The end profile is an Archimedean spiral. With the hob made of this basic worm, it is simpler and more convenient to manufacture and test the hob tooth shape than the involute worm. However, there is a slight amount of tooth error. However, this error is within the allowable range. For this reason, the basic worm of most of the finishing hobs in production uses the Archimedean worm instead of the involute worm.
3. The profile in the normal straight worm gear section of the normal straight worm gear is a straight line, and the end profile is an extended involute. Using this basic worm instead of the involute basic worm as a hob, the design error of its tooth profile is large, so it is generally used as a large modulus, multi-head and roughing hob.
July 09, 2022
