Gear processing

Structure classification

Generally, there are gear teeth, tooth grooves, end faces, normal surfaces, tooth top circles, tooth root circles, base circles, and indexing circles.

Gear tooth

Short for tooth, it refers to each convex part on the gear for meshing. These convex parts are generally arranged in a radial manner. The teeth on the matching gear contact each other, which can make the gear continuously mesh.

Alveolar

Is the space between two adjacent teeth on the gear; The end face is the plane perpendicular to the axis of the gear or worm on the cylindrical gear or worm.

end face

Is the plane at both ends of the gear.

Normal plane

Refers to the plane perpendicular to the gear tooth line.

Addendum circle

It refers to the circle where the top of the tooth is located.

Dedendum circle

It refers to the circle at the bottom of the groove.

Base circle

The generating line that forms an involute is a circle with pure rolling.

Graduation circle

It is the reference circle for calculating the geometric dimension of the gear in the end face.

main parameter 

Number of teeth Z

Generally, the speed of closed gear transmission is high. In order to improve the stability of transmission and reduce impact vibration, it is better to have more teeth. The number of teeth of pinion can be taken as z1=20~40. Open (semi-open) gear transmission, because the gear teeth are mainly worn out, in order to prevent the gear from being too small, it is not appropriate to select too many teeth for the pinion, generally z1=17~20.

Helix angle

β >  0 is left-handed;

β <  0 is right rotation

Pitch

pn=ptcos β (subscripts n and t represent the marks of normal direction and end face respectively)

modulus

Modulus refers to the quotient obtained by dividing the pitch (mm) by the circumference π, or the quotient obtained by dividing the diameter of the indexing circle (mm) by the number of teeth. (Note: Normal modulus is defined on the normal section of the basic rack)

Module is one of the most basic parameters of modular gear teeth. The module of straight and helical involute cylindrical gears can refer to the standard module series table (GB/T 1357-2008). [9] 

mn=mtcos β

m=p/ π

The gear indexing circle is the benchmark for designing and calculating the size of each part of the gear, and the circumference of the gear indexing circle=π d=z p

The module m is a basic parameter that determines the gear size. If the gear with the same number of teeth has large module, its size is also large.

pressure angle

α  rb=rcos α= 1/2mzcos α

At the tangent point P of the two gear pitch circles, the sharp angle between the common normal of the two tooth profile curves (i.e. the stress direction of the tooth profile) and the common tangent of the two pitch circles (i.e. the instantaneous movement direction at point P) is called the pressure angle, also known as the meshing angle. For a single gear, it is the tooth shape angle. The pressure angle of standard gears is generally 20 ". It is also used in some occasions α= 14.5 °, 15 °, 22.50 ° and 25 °.

Indexing circle diameter

d=m*z

Center distance

a=1/2*m(z1+z2)

Proper Meshing Conditions 

m1=m2, α 1= α 2, β 1= β two

In order to prevent the gear from undercutting α= The standard straight edge cylindrical gear of 20o shall be taken as z1 ≥ 17. Z2=u·z1。

Addendum height coefficient and backlash coefficient

—h*a 、C*

When two gears mesh, the tooth top of one gear always enters into the tooth root of the other gear. In order to prevent thermal expansion from jacking up and have space for storing lubricating oil, the tooth root height is required to be higher than the tooth top height. For this reason, the addendum height coefficient and the backlash coefficient are introduced.

Normal teeth: h * a=1; C *=0.25 short tooth: h * a=0.8; C*=0.3