With sufficient increase in the thrust force in the drilling process, the web thickness of the drill and the relief angle increase; otherwise, the drill point angle and the helical angle
decrease [21, 22].
The parameters of the mating gears are: normal module [m.sub.n], pinion and wheel number of teeth [z.sub.p] and [z.sub.w], normal pressure angle [[alpha].sub.n], pitch helical angle
[[beta].sub.p], center distance d, pinion and wheel moments of inertia [I.sub.p] and [I.sub.w], pinion and wheel loads [M.sub.p] and [M.sub.w], teeth contact stiffness K and damping D.
where [beta] is the helical angle
; [T.sub.i] is the mean torque applied to gear-i; [[phi].sub.ik] = [[psi].sub.k] - [[delta].sub.ik][[alpha].sub.i], where [[alpha].sub.i] is the transverse operating pressure angle and [[delta].sub.ik] = 1 for external gear pair and [[delta].sub.ik] = -1 for internal gear pair; [k.sub.ik] is the meshing stiffness of gear-i and planet gear-k; [h.sub.ik] = 0 if the teeth lose contact and otherwise [h.sub.ik] = 1 according to the assumption of solid-solid contact; [e.sub.ik] is the static transmission error (TE) excitation function.
 analyze the factors that influence the efficiency of a ball screw and provide the formula for efficiency based on contact angle and helical angle
. Wei and Lin  further study the BSM based on the research result of .
Q: How much helical angle
should I use with my fletching?
The rotors have trapezoidal cutters on a helical angle
, not perpendicular to the rotor axis, making a staggered cut that reportedly uses less energy and is less likely to jam.
The helical angle
of the flute depends on the type of material being tapped.
You get this with large fletching set to an aggressive helical angle
. This creates maximum drag and spin to bring a poorly released hunting arrow under control fast, for the best possible accuracy under difficult shooting conditions.