What Is a Thread Angle?

The lead angle is also called "thread rising angle". On a medium diameter cylinder or a medium diameter cone, the angle between the tangent of the spiral and the plane perpendicular to the thread axis. In worm gear transmission, the worm lead angle is the angle between the tangent of the spiral on the worm indexing cylinder and the end surface of the worm.

Lead angle: is the angle between the circumferential line and the spiral line of the middle diameter of the thread. Calculation method: tangent alpha = lead ÷ (medium diameter × 3.14).

the difference:

1. The acute angle between the tangent of the cylindrical spiral line on the cylindrical surface and the straight generatrix of the cylindrical surface passing through the tangent point is called the spiral angle

2. On a conical surface, the acute angle between the tangent of the conical spiral and the straight generatrix of the conical surface passing through the tangent point is also called the helix angle.

3, by

The worm lead angle is the angle between the tangent of the spiral on the worm indexing cylinder and the end face of the worm

(1) In the middle plane, in order to ensure the correct transmission of worm and worm gear

Selection of lead angle material

1. It has excellent processing performance, can obtain good surface finish and less residual internal stress, and has less effect on tool wear.

2. The tensile limit is generally not less than 588 MPa.

3. It has good heat treatment processability, good hardenability, hard to crack, uniform structure, small heat treatment deformation, and can obtain higher hardness, thereby ensuring the wear resistance and dimensional stability of the worm.

4. The hardness of the material is uniform, and the metallographic structure meets the standard. Commonly used materials are: T10A, T12A, 45, 9Mn2V, CrMn and so on. Among them, 9Mn2V has good processability and stability, but poor hardenability; the advantage is that the deformation after heat treatment is small, suitable for making high-precision parts, but it is easy to crack, the grinding process is poor, the higher the hardness of the worm, the more wear-resistant, However, it is not easy to grind during manufacture.

Lead angle positioning base selection

The set worm uses the inner hole to process the base surface, so the inner hole should be finished first, and then the outer circle and the supporting journal should be processed with the inner hole as the base surface. The thread processing is also based on the inner hole as the base surface, so a mandrel is required. Generally, the precision requirements of the inner hole of precision indexing worms are very high, and some need to be ground to ensure the accuracy. Generally, the inner hole of the precision indexing worm should be no less than level 1 accuracy, the surface roughness should be no less than 0.12, and the end face of the inner hole should be no less than 0.005mm. When the worm is mounted on the mandrel, it should first check whether the radial runout of the shaft shoulders at both ends is within the specified tolerance. Each subsequent process should be checked. When the worm is assembled, the shaft shoulders at both ends should also be checked. For radial runout, the accuracy of the mandrel must be equal to or higher than the accuracy of the shaft that matches the set worm.

The overall worm uses the center hole as the processing base surface. The requirements for the center hole are very high. There should be a taper to ensure the smoothness and contact area. The center hole should be checked and corrected before each process. The bearing journal should be the same as the center hole. Axiality and its geometrical accuracy. Before semi-finishing and finishing operations, you should check whether the radial, runout and axial runout of the bearing journal are within tolerances. ^[3]

Lead angle process route

1.Unquenched

Material preparationnormalizingrough turning (modulation) semi-finished turning outer circle, rough turning spiral surface artificial aging precision turning (finishing) inner hole end face key slot semi-finished turning Spiral surface-pliers (complete incomplete teeth)-semi-finished outer circle-fine-ground spiral surface-low temperature aging-research center hole-fine-ground outer circle-fine-ground spiral surface

2.Carburizing and quenching

Forging-annealing-rough turning-normalizing-semi-finished car outer circle and spiral surface-pliers (complete incomplete teeth)-carburizing-fine car outer circle (to remove the carburized part)- Quenching and temperinggrinding center holeturning threadmillingsemi-finished outer circlesemi-finished spiral surfacelow temperature aginggrinding center holefinished outer ring and end face Refined spiral surface

Installation of lead angle workpiece

1. Installation between double centers: Drill center holes at both ends of the solid shaft, install cone plugs or cone sleeve spindles with center holes at both ends of the hollow shaft, and use center holes at both ends of the lathe spindle and tailstock center shaft Mounting method of the workpiece.

2. When using the follower tool holder or the center to install long shaft parts, use the follower tool holder or the center holder to contact and support the outer surface of the shaft to enhance the rigidity of the workpiece and improve the machining accuracy. The tool holder is installed on the Chengchuang mop and moves with the mop during cutting. The center frame is installed separately in the middle of the shaft. ^[1]