Spur Gear Designing: Pitch Circle or Base Circle First?

[wings_of_fire]

Hi,

I know basics of gear design but have never designed a gear before. I want to know, while designing a spur gear what is defined first 1] Pitch Circle or 2] Base Circle ?

In case. if base circle is defined first, then how to determine its diameter ?

Lot of design materials explain how to design a gear on a very surface level. I have gone through lot of material on gear design before posting this querry but I was unable to find the answer. please guide me.

 

[minger]

The pitch circle is typically defined first as that is essentially the standard "distance" between centerlines of the gearset. From here, you then can typically just use addendum and deddendum factors to adjust the OD and base circle.