What is a tip circle ?
A tip circle is the circle obtained by connecting the tooth tips of a gear.
The tip circle and the root circle are visible while the pitch circle is imaginary and cannot visually be seen.
Figure below illustrates the tip circle.
It should be noted that in profile shifted gears, the tip circles become larger for a positive (plus) shifted gears, while for a negative (minus) shifted gears, the tip circles become smaller.