# Here are all the answers you want to know about helical gears!

#### How is the profile of helical involute curved surface of helical gear formed?

Answer: when the generating surface of the involute rolls on the base cylinder, a line with a β B angle with the generatrix of the base circle on the generating surface forms the involute spiral surface of the helical gear teeth.

#### Is the helix angle of each coaxial cylindrical surface helix where the helical gear tooth profile is located the same? Why?

Answer: the helix angle is different. Because the helix angle β I is determined by the lead L and the diameter Di of the cylinder, the lead is the same, and the diameters of each circle are different, so the helix angle is different, and the relationship is TG β I = L / π di

#### What are the characteristics of helical gear engagement?

Answer: 1) the tooth profile of the two wheels starts to contact from the point, and the contact line grows from the short to the long, and then shortens, until the point contacts, and then disengages from the engagement. Unlike the straight tooth cylindrical gear transmission, the contact suddenly disengages along the entire tooth width, but gradually enters into the engagement and gradually disengages from the engagement, so the impact is small and the transmission is stable.

2) Large coincidence

ε= εα+εβ

#### Which is the standard parameter surface of helical gear and which is the standard involute? Explain why.

Answer: the normal surface is the standard parameter surface. Theoretically, the end face is a standard involute, because the involute is formed by the pure rolling of the generating surface on the base cylinder, and the track of the oblique line on the generating surface is an involute. In machining, the normal surface is the standard involute, because the standard cutter for machining the helical gear profile is used for machining the straight cylindrical gear, its cutting movement direction is tangent to the helix, and the cutter surface is on its normal surface, so the normal surface is the standard Zhejiang Kaixian line.

#### What is the relationship between the end face of helical gear and the geometric parameters of normal face, and why is the end face parameter required?

Answer: Mn = MT cos β, TG α n = TG α t cos β B, h * at = h * ancos β, c * t = C * ancos β because the geometric dimensions are DT, DBT, DAT, DFT, Pt, PBT of the end face.

#### What are the correct Meshing Conditions and continuous transmission conditions for a pair of helical gears?

Answer: correct engagement condition: m N1 = m N2 = m α N1 = α N2 = α

External engagement β 1 = – β 2

Internal engagement β 1 = β 2

Continuous transmission condition: ε = ε α + ε β ≥ 1

#### What is the equivalent gear and equivalent number of teeth of helical gear? What is the purpose of equivalent number of teeth?

Answer: the straight cylindrical gear equivalent to the normal profile of the helical gear is called the equivalent gear of the helical gear. The number of teeth of an equivalent gear is called the equivalent number of teeth.

The number of equivalent teeth is an important basis for selecting the tooth shape of the cutter in the process of gear copying, and the number of equivalent teeth is the main basis for the strength design of the gear. 