Page 111 - Mechanical Engineer's Data Handbook

100 MECHANICAL ENGINEER’S DATA HANDBOOK

Coefficient of friction for worm gears

Velocity (m s- *)
0.5 1 .o 2.0 5.0 10.0 20.0

Hard steel worm/phosphor bronze wheel 0.06 0.05 0.035 0.023 0.017 0.014
Cast iron worm/cast iron wheel 0.08 0.067 0.050 0.037 0.022 0.018

2.10.7 Epicyclic gears Let :
N = speed
The main advantage of an epicyclic gear train is that n = number of teeth
the input and output shafts are coaxial. The basic type Note that a negative result indicates rotation reversal.
consists of a ‘sun gear’ several ‘planet gears’ and a ‘ring
gear’ which has internal teeth. Various ratios can be
obtained, depending on which member is held station-
ary.

Ratio of output to input speed for various types