The rack also divides the straight tooth rack and the helical tooth rack, and pairs with the straight tooth cylindrical gear and helical tooth cylindrical gear respectively;The tooth profile of the rack is a straight line instead of an involute (a plane for the tooth surface), which is equivalent to a cylindrical gear with an infinite dividing circle radius.
The main features
(1) since the rack tooth profile is a straight line, all points on the tooth profile have the same pressure Angle, which is equal to the inclination Angle of the tooth profile. This Angle is called the tooth profile Angle, and the standard value is 20°.
(2) the tooth spacing and modulus are the same on any line parallel to the tooth top line.
(3) the straight line parallel to the tooth top line and with tooth thickness equal to the width of tooth groove is called dividing line (middle line), which is the reference line for calculating the rack size.Parameter selection (1) gear run-out, full tooth depth, common normal, tooth direction is qualified or not, tooth pendulum difference, circumferential error is out of tolerance.(2) whether the mounting distance is suitable after the installation of the gear and rack.(3) the meshing gap of rack and gear should be 0.25 modulus.
(4) rack tooth depth, beating, common normal line, especially the tooth direction is qualified.