Power Jacks M-Series - Machine - Manual (Page 7)

7
Imperial Series – Machine Screw Jacks
5a On 5-ton and 35-ton models, press load bearing cones onto worm gear (6A) or worm gear nut
assembly (6B). Small end of bearing cone should face away from gear teeth.
6. Install worm gear (6A) or worm gear and nut assembly (6B) in shell (3).
Caution: Strike each end of worm shaft sharply with a wooden mallet to seat bearing
properly. Recheck flange bolts for tightness. Worm should turn freely with
minimum drag and end play. if too much end play is present, remove shims as
required. If worm does not turn freely, add shims as required.
7. Install top load bearing (7) (bottom load bearing (8) for 100 and 150-ton models on worm gear (6A) or
worm gear and nut assembly (6B).
8. Fill housing fully with grease.
9. FOR ALL MODELS EXCEPT 100 AND 150-TON – Install shell cap (2) and screw down until tight.
Note:
Shell cap flange does not necessarily have to bear against top shell, there will usually be a
gap. This will put a slight drag on worm. If worm is hard to turn, back off slightly on shell cap.
FOR 100 AND 150-TON MODELS – Install base plate and screw down base plate until tight.
Note:
This should put a slight drag on the worm. If the worm is hard to turn, back off slightly on the
base plate. Be sure base plate does not project past base surface of housing.
10. Lock shell cap in place with set screws (lock screw on 100 and 150-ton models)
11. FOR ALL MODELS EXCEPT 100 AND 150-TON – Screw bottom pipe (4) into shell (3) (upright
models) or into shell cap (2) (inverted models)
FOR 100 AND 150-TON MODELS
– Screw bottom pipe into base plate (upright models) or into shell
(inverted models)
12. Brush lifting screw (5) with a light film of grease and install in actuator. On inverted models, install guide
bushing (16) and then install lifting screw (5).
13. If screw jack is keyed, install key in shell cap (2) (shell for 100 and 150-ton models) and bolt in place.
14. Operate unit to ensure proper functioning of all components prior to reinstallation.
3.8 Anti-Backlash Nut Function
As shown in Figure 3-1, the worm gear (2) and anti-backlash nut (3) are printed together with guide pins.
The threads in the anti-backlash nut work in opposition to the threads in the worm gear as they engage the
threads of the lifting screw (1). Adjustment of backlash is made by running down on the shell cap of the
screw jack. This forces the anti-backlash nut threads into closer contact, reducing clearance and thus
reducing backlash.
3.9 Anti-Backlash Nut Adjustment
1. To minimise backlash remove the two set screws
(4) and tighten down on shell cap until the desired
backlash is obtained. Spot drill top of shell through
set screw holes, then replace set screws and tighten
to prevent shell cap backing off.
2. To avoid binding and excessive wear, do not adjust
lifting screw backlash to less than 0.002 inch.
3. The clearance (A) designed into the worm gear and
anti-backlash nut is set one-half the thread thickness.
When adjustments have been made to use all this
clearance replace the worm gear and anti-backlash
nut as a set.
Figure
3-1 Anti-backlash Nut Adjustment