Help computer rack parameters.

Racks generally need to be used in conjunction with gears. The main parameters of rack and pinion are tooth height, tooth thickness, tooth root height, tooth top height, tooth root circle radius, tooth slot width and pressure angle.

I. Rack and pinion parameters:

1, tooth height: the distance from the tooth tip to the tooth root is determined by the modulus.

2. Tooth thickness: the reference value of tooth thickness is 1/2 pitch.

3. Tooth root: the part between the indexing circle and the tooth root circle.

4. Tooth crest: the part between the indexing circle and the tooth crest circle.

5. Tooth root height: the distance from the tooth root to the scale line.

6. Tooth tip height: the distance from the tooth tip to the scale line.

7. Radius of tooth root circle: the minimum curvature radius of tooth root transition surface.

8. Slot width: The distance between two adjacent teeth can be divided into two types: end slot width and normal slot width.

9. Pressure angle: the inclination of gear tooth surface.

Secondly, several aspects need to be considered when selecting the parameters of the rack and pinion:

1. Whether the installation distance of the rack and pinion is appropriate after installation.

2. Whether the gear runout, full tooth depth, common normal and tooth direction are qualified, and whether the pitch error is out of tolerance.

3, rack tooth depth, bounce, common normal, especially the tooth direction is qualified.

4, rack, gear meshing clearance should be 0.25* modulus, etc.

Extended data

Machining method of rack and pinion: (1) hobbing (2) grooving (3) shaving (4) grinding (5) honing.

gear hobber

Machining the tooth surfaces of gears, worm gears, etc. Generating method with gear hob.

The principle of machining gears with gear hob on hobbing machine is equivalent to the principle of meshing a pair of spiral gears.

Hob is essentially a spiral gear with large helix angle. Because of the small number of teeth (the number of teeth of single-head hob K= 1) and the long teeth, it can turn around the shaft many times, so it becomes a worm with small helix angle-the basic worm of hob. This kind of worm becomes a gear hob with cutting edge and front and rear angles after grooving and shoveling teeth.

The generating motion of gear hob and machined gear is shown in figure 16-8. When the hob rotates, it is equivalent to the axial movement of a toothed bar, which is equivalent to the meshing movement of an imaginary rack and a machined gear. Therefore, there are the following requirements between hob and machined gear:

(1) The normal module mn cutter and the normal tooth angle α of the hob should be equal to the corresponding parameters of the gear to be machined.

(2) The hob and the gear to be machined must strictly keep the meshing motion relationship of a pair of spiral gears, namely:

Where n is the hob speed per minute;

N-the speed of the workpiece per minute;

Z- the number of teeth of the workpiece;

K—— Number of hob heads.

(3) In order to make the spiral direction of the hob consistent with the tooth direction of the gear to be machined, the axis of the hob should be inclined to the end face of the gear by an installation angle γ-An, and γ-An =λf when hobbing spur gears, where λf is the spiral angle of the hob. When hobbing a helical gear, γ A = βf λ F, where βf is the helix angle of the gear to be machined. When the spiral direction of hob and workpiece is opposite, take "+"sign, and when it is the same, take "-"sign.

In gear hobbing, in addition to the rotation (cutting motion) of the hob and the generating motion between the hob and the workpiece, the hob also needs the feed motion δ axis along the axial direction of the workpiece, which constitutes the basic motion of gear hobbing.

These three basic movements are also necessary when hobbing helical gears, but because the teeth of helical gears are spirals along the tooth width, it is necessary to feed the S-axis axially with a hob and rotate the workpiece additionally. That is to say, the workpiece and the hob are required to strictly maintain the generated motion relationship. When the hob moves axially to a lead T of the workpiece, the workpiece has more or less additional motions.

Gear hobbing is the most commonly used method of gear cutting. Can process straight, helical and variable profile cylindrical gears. General hobbing accuracy can reach 7 ~ 8, and the highest accuracy can reach 4 ~ 5 or even 3. Because the whole cutting process of hobbing is continuous, the productivity is high.

gear-shaping

Machining the tooth surfaces of internal and external gears or racks by generating method or forming method with gear shaper cutter.

Gear shaping, like hobbing, is also processed by generating method. The gear shaper cutter is like a gear with front and back angles and is shaped like a cutting edge, so the machining principle of the gear shaper cutter is equivalent to the meshing principle of a pair of cylindrical gears with parallel axes.

During gear shaping, the gear shaper cutter moves up and down, and the cutting speed is expressed by double strokes per minute. Similarly, the gear shaper cutter and the gear to be machined must keep the meshing motion of a pair of cylindrical gears, namely:

Where n cutter, n power-gear shaper cutter and the rotating speed of the workpiece;

Z- cutter, Z- cutter-number of teeth between gear shaper cutter and workpiece.

At the beginning of gear shaping, in order to gradually cut to the full tooth depth, the gear shaper cutter must have radial feed movement, and the radial feed δ diameter is expressed by the radial feed times of each double stroke of the gear shaper cutter. When cutting to the adjusted depth, the radial feed automatically stops. The radial feed process and feed amount are generally controlled by cams.

When the gear shaper cutter reciprocates up and down, the downward motion is cutting motion, and the upward motion is idle stroke. In order to avoid scratching the machined tooth surface during idle stroke and reduce the wear of the gear shaper cutter, the cutter is needed to move the workpiece.

Generally, the accuracy of gear shaping can reach 7 ~ 8 grades, and the highest can reach 6 grades.

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