the publications the only way to obtain a force model is by lab test there are many types of inserts used today for roller cone bit depending on the rock type drilled if the single insert force model is used a lot of tests have to be done and this is very difficult if not impossible by using the element force model only a few tests may be enough because any kind of insert or tooth can be always divided into elements in other words one element model may be applied to all kinds of inserts or teeth after having the single element force model the next step is to determine the interaction between inserts and the formation drilled this step involves the determination of the tooth kinematics local from the bit and cone kinematics global as described below 1 the bit kinematics is described by bit rotation speed u03c9 rpm revolutions per minute and the rate of penetration rop both rpm and rop may be considered as constant or as function with time 2 the cone kinematics is described by cone rotational speed each cone may have its own speed the initial value is calculated from the bit geometric parameters or just estimated from experiment in the.