27
NOTICE
11. Backlash Adjustment of Worm Gears
The worm shaft and worm wheel are made of the special materials and they are accurately machined.
The dual lead worm system is adopted for eliminating the backlash of worm gear. It changes the lead of
right and left teeth of worm shaft a little and adjusts the backlash for the worm wheels by shifting this
worm shaft in the axis direction.
This dual lead worm system can adjust the backlash finely without changing an ideal engagement state
and it is theoretical and most secure backlash adjustment method.
Although the backlash of worm gear has already been adjusted before shipping, it is necessary to adjust
the backlash when the machine is operated for a long period of time. The proper values for backlash are
shown in the following list. These are values when the machine is cooled. Thus, they are values after
interrupting for a long period of time. Consequently, when the machine is operated for a long period of
time, the backlash becomes small in comparison with the following values.
If backlash is too small, the worm gear will cause seizing.
○
Adequate Backlash
TT200
Circular arc length at peripheral table position (
μ
m)
Converted angle (sec.)
Rotating axis
14
～
42
29
～
86
Tilting axis
8
～
17
14
～
29
When adjusting the backlash, measure the current backlash by the following method. After that, adjust it.
This adjustment affect the indexing accuracy and worm wheel durability, thus it is strongly recommended that
a skilled technician should do the adjustment. Please consult Kitagawa distributor before the adjustment.
11-1. Backlash measuring method of worm gear of rotating axis
1
）
Set the dial gauge the periphery of the guide block on the table top face.
2
）
Read the value of dial gauge at the position where the table stops after rotating the table slowly in
one way with the flat steel or round bar inserted in the guide block on the surface of table (with worm
wheel gear tooth attached). At this time, for the torque added to the table, refer to the list created
later. Next, rotate the table under the same condition in the reverse direction to read the value of dial
gauge. This difference of measured values is the backlash.
3
）
Perform the above measurement at 8 positions by rotating the table and compare them with the
above adequate values. (See Fig.6)
T = F
×
L
T: Torque (N
・
m)
F: Effort force (N)
L: Distance from table center to
point to add force F (m)
Fig.6
