The main differences are the method of copying and the method of rounding

The method of copying is based on the fact that the shape of the cog-wheel cavity repeats the profile of the grinding wheel, which is being processed.

    Pros:

  • Simplicity of obtaining a modification along the tooth profile and modification along the tooth line (barrel modification). Modifications are used to obtain the most advantageous location of the contact patch, eliminates edge contact of the teeth (especially high-loaded gears), reduces noise in the transmission.
  • Higher productivity with fewer teeth.
  • The possibility of straightening a circle for processing gears with different profile angles with a single diamond roller.
  • The possibility of dressing the grinding wheel in the machining cycle with the subsequent automatic compensation of the allowance removed during the correction. This increases the stability of obtaining the wheel's precision parameters.

The rolling method  is based on the reproduction of the gear engagement (workpiece) and the worm wheel (tool), which results in an involute profile on the gear wheel. To implement this method, precise synchronization of the rotation of the worm grinding wheel and the machined gear wheel is necessary.

    Pros:

  • A higher productivity when machining gears with a large number of teeth.

    Minuses:

  • The complexity of adjustment for obtaining modifications.
  • The complexity of changing over when changing over to another type of product (setting the diamond rollers to a different tooth width, changing the rollers when grinding wheels with a different profile angle, etc.)
  • Higher cost of grinding wheels.

The pros and cons of each method determined the scope of their application. The method of rolling is used, mainly in mass production, the method of copying - in small-scale and serial production.

Historically, the first method for processing gears was the rolling method. This is due to the fact that the shaping motion: uniform rotation of the grinding wheel, uniform rotation of the gear wheel, uniform movement along the axis of the gear wheel, are easily realized on machines without using the CNC. Also, when straightening a grinding wheel, diamond rollers of a simple profile (cone) are used. The method of copying without the use of a computer for calculating the profile and without the CNC for machine control is quite difficult to implement. With the modern development of computer technology and numerical control, all the difficulties in implementing the method of copying have receded into the background.