Observe that our D1 value is falling in the range. The below empirical formula is the cross check for the correctness of the whole design calculation:.Now, we can calculate the centre to centre distance ( C) by the following equation:.The following AGMA empirical formula to be used for calculating the pitch circle diameter of the gear ( D2):.Calculate the pitch circle diameter of the worm ( D1) by using the below AGMA empirical formula:.By using the two equations ( Eqn.1 & Eqn.2), we will get the approximate values of.Now use the following AGMA empirical formula:.Say, we are going ahead with the Module as 2 and the Pitch as 6.238. Select the suitable module and its corresponding pitch from the following AGMA specified table: Now, let’s say we have the following design input:Īnd, we have to find out the Module (m), Pitch (P), Number of helix of Worm (T1), Number of teeth of Gear (T2), Pitch circle diameter of Worm (D1), Pitch circle diameter of Gear (D2), Centre to centre distance(C).Also, the module of the worm as well as the gear must be equal for a mating worm and gear.We will use the term Pitch (P) for both the pitch in this tutorial. The axial pitch of the worm and the circular pitch of the gear must be same for a mating worm and gear.Design calculations of the other aspects of the worm gear will be discussed in a subsequent part of the tutorial. We will use the AGMA formulae for doing the calculations. This worm gear design tutorial will discuss up to the selection of the module and pitch and the calculation of the number of teeth, pitch circle diameter and centre to centre distance between the worm and gear. Look at the picture below:Ĭ – Centre to Centre Distance between the Worm and the Gear A worm gear box must contain a worm and a mating gear (helical gear) and normally the axis of the worm is perpendicular to the axis of the gear.