For two meshing spur gears on parallel shafts, what is the effect on the gear train if the module of both gears is increased while keeping the number of teeth constant for each gear? 

Concept:

In gear systems, the module (m) is a measure of the size of gear teeth and is defined as:

\(m = \frac{d}{z}\), where d is the pitch circle diameter and z is the number of teeth.

Rearranging the formula, the pitch circle diameter is:

\(d = m \cdot z\)

Calculation:

For two meshing spur gears with pitch diameters d₁ and d₂, and modules m and tooth counts z₁, z₂, we have:

\(d_1 = m \cdot z_1\)  and  \(d_2 = m \cdot z_2\)

The center distance between the two gears is:

\(C = \frac{d_1 + d_2}{2} = \frac{m(z_1 + z_2)}{2}\)

If the module m is increased while keeping z₁ and z₂ constant, the center distance C will increase proportionally.