JLG M600 Service Manual - Manual (Page 135)

SECTION 4 - BOOM & PLATFORM
3121813 – JLG Lift – 4-25
4.5 JIB ROTATOR
Operating Principle
Helac’s helical hydraulic rotary actuators use our sliding
spline technology which converts linear piston motion into
powerful shaft rotation. The actuators are composed of a
housing and only two moving parts, the central shaft and
the annular piston. Helical spline teeth machined on the
shaft engage matching splines on the inside diameter of
the piston. The outside diameter of the piston carries a
second set of splines, of opposite hand, which engage
matching splines in the housing’s ring gear. As hydraulic
pressure powers the piston back and forth within the
housing – similar to the operation of a hydraulic cylinder –
the splines cause the shaft to rotate.
Disassembly
1. Remove all hydraulic fittings Drain the oil from both
sides of the piston through the pressure ports.
2. Place the actuator horizontally on a clean work
bench with ample room to place the internal parts as
they are removed.
3. Unthread the socket head cap screws (102) from the
lockwasher(05). Remove the lock washer from the
shaft (02).
4. Secure the actuator firmly to the work surface to pre-
vent movement. A pipe vise works well. Insert two
long screws (1/4-20) into the end cap (04) and,
using a pry bar, unthread the end cap from shaft by
Bars indicate starting positions of piston
and shaft. Arrows indicate direction they
will rotate. The housing’s ring gear
remains stationary.
As fluid pressure is applied, the piston is
displaced axially while, simultaneously...
... the helical gearing forces the rotation of
the shaft. Note how the double helix
design compounds rotation: shaft rotation
is about twice that of the piston.
Figure 4-12. Operating Principle - Jib Rotator