Form Tools.

• Most metal cutting processes produce the desired surface by generating.

• In generating, the desired surface is produced by suitably combining the cutting speed and feed motions of the machine. The surface generated does not take the shape of the tool.

• Some complex shapes which are difficult to generate can be produced by forming using form tools. These tools have the same shape as the shape desired and reproduce their shape on the job in reverse.

• During cutting, form tools are given only a small radial movement every time and no axial movement.

• These types of tools are used for form grooving, taper turning, gear cutting, and many similar operations.

• They are also used on some large quantity production machine tools.

• In general, these tools are costlier than generating tools and are limited to smaller sizes because larger sizes are liable to chatter.

• Form tools are used for machining profiles o relatively small width. For larger widths copy turning is more desirable.

• Use of form tools leads to following advantages:

1] High production rate.

2] Uniform contouring of all work pieces.

3] Accurate dimensions.

• Most form tools are made of H.S.S. However using contoured cemented carbide tips leads to increased productivity of 30 to 40 percent compared to H.S.S. form tools.

• When designing form tools it is necessary to provide suitable rake and relief angles on the tool so that the cutting can occur easily. Tables 7.3.1 and 7.3.2 give recommended values of rake and relief angles to be used.

Table 7.3.1 : Recommended rake angles for form tools.

Table 7.3.2 : Recommended relief angles.