What is non-standard installation center distance? What are the features of non-standard installation?
Answer: a pair of meshing transmission gears, the installation of which pitch circle does not coincide with graduation circle is called non-standard installation, and the center distance is called non-standard installation center distance.
Characteristics: R ≠ R ′, a ≠ a ′, a ′ = R1 ′ + R ′ 2 = < R1 + R2) cos α / cos α′, i.e. a ′ ≠ a α ′ ≠ α R1 ′ ≠ R1 R2 ′ ≠ R2 C ′ ≠ C, there is backlash, resulting in impact, the degree of coincidence decreases, and the stability is poor.
What are the characteristics of gear rack meshing transmission?
Answer: 1) the position of the meshing line does not change due to the change of the relative position between the gear and the rack. It is always a fixed line tangent to the base circle and perpendicular to the linear profile of the rack.
2) R = R ′ α′ = α = rack angle
What are the characteristics of standard rack and pinion machining?
Answer: the graduation circle of the wheel blank is tangent to the center line of the rack tool, and the number of teeth of the gear to be processed is determined by the moving speed of the tool and the angular speed of the wheel blank to ensure that V tool = R ω.
What is undercutting phenomenon of involute profile? What is the reason?
Answer: when the gear is processed by the generating method, the phenomenon that the processed involute profile is cut off is called undercut phenomenon.
Cause: the intersection of the tooth top line and the meshing line of the cutter exceeds the meshing limit point of the gear to be cut. The reason why the tooth top line of the cutter exceeds the meshing limit point is that the number of teeth of the gear to be machined is too small, the pressure angle is too small, and the tooth top height coefficient is too large.
How to determine the minimum number of teeth without undercutting for standard external gear?
Answer: it is determined by Zmin = 2H * A / sin2 α.
What is a shift gear?
Answer: the gear whose index circle tooth thickness is not equal to the width of the tooth slot and the gear whose tooth top height is not the standard value are called shift gears. In machining, a gear whose center line of rack tool is not tangent to the graduation circle of the gear to be machined is called a modified gear.
What are displacements and coefficients and minimum coefficients?
A: displacement: the vertical distance that the center line of the tool is shifted by the position of the machining standard gear. Modification coefficient: the coefficient required to express the modification amount with standard modulus. Minimum modification coefficient: the minimum value of modification coefficient required for undercutting of involute gear.
xmin = h*a <Zmin – Z）/ Zmin
Compared with the standard gear, which dimensions of the modified gear with the same number of teeth have changed, which dimensions remain unchanged, and why?
Answer: the number of teeth, modulus, pressure angle, graduation circle, base circle, graduation circle pitch, full tooth height remain unchanged, and the tooth top circle, tooth root circle, graduation circle tooth thickness and tooth slot width have changed.
Reason: the machining method of the modified gear with standard gear cutter is the same, i.e. the correct meshing condition is the same, so the module and pressure angle of the graduation circle are the same. Therefore, it can be seen from the formula that the pitch circle and the base circle are the same, and then there are the calculation of the tooth root height, the tooth top height, the tooth root circle and the tooth term circle. The benchmark is the pitch circle. When machining the modified gear, if the center line of the standard tool moves from the pitch circle to the outside, the tooth root circle becomes smaller, and the tooth root circle becomes larger. If the whole tooth height is to be kept constant, the tooth top height becomes larger, and the tooth top circle becomes larger, because the tool moves outward at the gear pitch circle The thickness becomes smaller, that is to say, the tooth slot processed becomes smaller, and the tooth thickness becomes thicker because the pitch circle is the same.