Davidbrown tangent comparator & Constant chord method

Davidbrown tangent comparator

 BASE TANGENT Method: 

•In  this  method,  a  span  of  convenient number  of  teeth  b/n  two  parallel  planes which are tangential  to opp tooth flanks are  measured  with  the  help  of  David Brown tangent comparator.

Constant chord method

Now let us move to the another method of measurement of tooth thickness that is constant chord method in this diagram we can see the w is chordal thickness is measured at the pitch line at depth of d now the expressions chordal thickness expressions and the depth expressions used for measurement for calculated for tooth thickness these expressions contain the value N that is number of teeth. Both the expressions w and depth contains the number of teeth N if a large number of gears for a number of set each having different values of N are to be tested then separate calculations would become laborious.

In such cases the method of constant chord is useful method so this constant chord is used in dimension since it has the same nominal value for all gears of a common system irrespective of number of teeth provided that the backlash allowance is same on all gears.